SuSy Activity Research Articles

Improved yield by optimizing carbon, nitrogen metabolism and hormone balance in apical kernels under low nitrogen conditions using the low nitrogen–tolerant maize variety

ContextUsing low nitrogen (N)–tolerant maize varieties serves as a viable means to curtail N fertilizer application while improving crop yield. ObjectiveTo investigate the differences in carbon and nitrogen metabolic processes, and the hormones within kernels located at varying positions along the ear, between low N–tolerant and low N–sensitive maize varieties. Furthermore, this research aims to elucidate the ramifications of these observed disparities on kernel weight and yield, particularly when cultivated under low N conditions. MethodsThe low N–tolerant maize variety (ZH311) and low N–sensitive maize variety (XY508) were applied. The in–situ filed experiment with three N fertilizer treatments of 0 N (0 kg·N ha−1), 150 N (150 kg·N ha−1) and 300 N (300 kg·N ha−1) was conducted in 2017–2019. ResultsThe apical kernel weight of ZH311 was less affected by low N (0 N and 150 N) and the yield was 25.3–22.9% higher than XY508. The kernel weight was significantly and positively correlated with kernel starch and protein content. The starch and protein contents of ZH311 apical kernels were 6.3–7.3% and 12.4–14.4%, higher than XY508 under low N. It was indicated that the main factor affecting starch accumulation in the apical kernels was Susy activity and protein accumulation was IAA/GA3, Z+ZR/GA3 and GOGAT activity by the redundancy analysis. Under low N, the Susy and GOGAT activity, IAA/GA3 and Z+ZR/GA3 in the apical kernel of ZH311 were higher than XY508 by 51.4–39.3% and 65.4–46.9%, 62.1–33.1% and 41.8–48.2%. ConclusionsWe have demonstrated to improve the maize yield by increasing the apical kernel weight, which resulted in enhancing the uniformity of the kernel weight along the ear. Under low N conditions, the low N–tolerant maize variety was shown to facilitate the starch and protein biosynthesis by increasing the activity of key enzymes in the carbon and the nitrogen metabolism processes such as Susy and GOGAT in the apical kernels, and optimizing the hormone balance between IAA/GA3 and Z+ZR/GA3, to increase the kernel weight and yield. ImplicationsThe findings of this investigation will help understand the underlying factors contributing to the yield variations exhibited among distinct low N–tolerant maize varieties when cultivated under conditions of limited N availability. These insights could serve as the theoretical basis for breeding of low N–tolerant maize varieties and practical guidance for the formulation of N fertilizer management strategies.

Comparative Analysis of Sucrose-Regulatory Genes in High- and Low-Sucrose Sister Clones of Sugarcane.

Sugarcane is a significant primitive source of sugar and energy worldwide. The progress in enhancing the sugar content in sugarcane cultivars remains limited due to an insufficient understanding of specific genes related to sucrose production. The present investigation examined the enzyme activities, levels of reducing and non-reducing sugars, and transcript expression using RT-qPCR to assess the gene expression associated with sucrose metabolism in a high-sucrose sugarcane clone (GXB9) in comparison to a low-sucrose sister clone (B9). Sucrose phosphate synthase (SPS), sucrose phosphate phosphatase (SPP), sucrose synthase (SuSy), cell wall invertase (CWI), soluble acid invertase (SAI), and neutral invertase (NI) are essential enzymes involved in sucrose metabolism in sugarcane. The activities of these enzymes were comparatively quantified and analyzed in immature and maturing internodes of the high- and low-sucrose clones. The results showed that the higher-sucrose-accumulating clone had greater sucrose concentrations than the low-sucrose-accumulating clone; however, maturing internodes had higher sucrose levels than immature internodes in both clones. Hexose concentrations were higher in immature internodes than in maturing internodes for both clones. The SPS and SPP enzymes activities were higher in the high-sucrose-storing clone than in the low-sucrose clone. SuSy activity was higher in the low-sucrose clone than in the high-sucrose clone; further, the degree of SuSy activity was higher in immature internodes than in maturing internodes for both clones. The SPS gene expression was considerably higher in mature internodes of the high-sucrose clones than the low-sucrose clone. Conversely, the SuSy gene exhibited up-regulated expression in the low-sucrose clone. The enhanced expression of SPS in the high-sucrose clone compared to the low-sucrose clone suggests that SPS plays a major role in the increased accumulation of sucrose. These findings provide the opportunity to improve sugarcane cultivars by regulating the activity of genes related to sucrose metabolism using transgenic techniques.

Drought stress reduces the photosynthetic source of subtending leaves and the transit sink function of podshells, leading to reduced seed weight in soybean plants.

Drought stress is the key factor limiting soybean yield potential. Soybean seed formation involves a coordinated "subtending leaf-podshell-seed" process, but little is known about the assimilation and transport of photoassimilates in subtending leaves, podshells and seeds or their relationships with soybean seed formation under drought stress. To address these research gaps, two-year experiments with two soybean cultivars, Wandou 37 (drought tolerant) and Zhonghuang 13 (drought sensitive), were conducted under three soil water content (SWC) conditions in 2020 and 2021 based on the responses of their yield to drought. We analyzed the photosynthetic assimilation and translocation of photoassimilates in subtending leaves, podshells and seeds by stable isotope labeling. Compared with those under 75% SWC, 60% SWC and 45% SWC significantly decreased the Wandou 37 seed weight by 19.4% and 37.5%, respectively, and that of Zhonghuang 13 by 26.9% and 48.6%, respectively. Compared with those under 75% SWC, drought stress decreased the net photosynthetic rate and the activities of sucrose phosphate synthase (SPS) and sucrose synthase (SuSy), which in turn decreased the photosynthetic capacity of the subtending leaves. The podshells ensure the input of photoassimilates by increasing the SuSy activity, but the weakened source-sink relationship between podshells and seeds under drought stress leads to a decrease in the translocation of assimilates from podshells to seeds. The lack of assimilates under drought stress is an important factor restricting the development of soybean seeds. We conclude that the decrease in seed weight was caused by the decrease in the photosynthetic capacity of the subtending leaves and the decrease in the overall availability of photoassimilates; moreover, by a decrease in the translocation of assimilates from podshells to seeds.

Impact of heat stress on sucrose metabolism of watermelon

High temperatures (HT) are a significant threat for crop production, and strategies for maintaining high crop yields and quality under HT stress are crucial agricultural objectives. The changes in sugar metabolism during HT stress were examined in watermelon cv. Crimson Tide leaves. The leaves obtained from plants were subjected to 35, 40, 45, 50, 55 and 60°C. Heat-stress tolerance (HST; LT50), hydrogen peroxide (H2O2), sucrose (Suc), reducing sugars and starch contents and some sucrolytic enzyme activities in leaf samples held at each temperature for 30 minutes were determined. The HST and H2O2 content, rose with increasing temperatures, most noticeably between 50-55°C. As a result, the LT50 value was determined to be 53.84°C. The Suc content increased almost 2-fold between 50-55°C. The reducing sugars and starch content sharply decreased with HT up to 50°C comparing to the control, however both increased almost 2-fold between 50-55°C. The H2O2 may act as a signal molecule at 40-45°C and triggers sucrose metabolism. It was determined that alkaline-INV and SuSy activities were at the maximum level at 40°C. The increase in enzyme activities has been associated with increased energy needs under stress conditions. The findings revealed that sugar metabolism contributes significantly to HST.

Nitrogen supply alleviates seed yield reduction by improving the morphology and carbon metabolism of pod walls in shaded rapeseed.

Shading significantly affects rapeseed yield, while reasonable nitrogen (N) application has efficiency gains. However, the functions and mechanisms of N are not fully established for shaded rapeseed plants. Therefore, we conducted a 2-year field experiment to study the effect of N on pod wall morphology and carbon metabolism of shaded rapeseed. Two varieties, three N rates (120 [N1], 240 [N2], and 360 [N3] kg hm-2 ) and two light intensities (100 and 70% light transmission) from 10 to 35 days after the end of flowering were set as experimental parameters. Shading decreased the pod wall chlorophyll content, ribulose 1,5-bisphosphate carboxylase (Rubisco) activity and glucose content at 25 and 35 days after flowering (DAF). Decreased sucrose synthase (SuSy) and sucrose phosphate synthase activity caused by shading reduced sucrose and fructose content. They are responsible for the decline in the 1000-seed weight and a 22.1-37.6% decline in seed yield. More N under shading promoted pod elongation and pigment content, improved chloroplast ultrastructure, increased Rubisco and SuSy activity at 35 DAF, thus contributing to pod wall photosynthesis and fructose and glucose levels in shaded rapeseed plants. Similar trends were observed in pod number, pod weight, and seed weight, while the greatest increase in seed/wall ratio was observed under N2 for shaded rapeseed plants. The results indicated that N can reduce the yield difference between different light conditions and balance partitioning and conversion of photoassimilates in pod wall, but avoid applying an excessive amount of nitrogen.

Combined effect of elevated temperature and drought stress on carbohydrate metabolism of cotton (Gossypium hirsutum L.) subtending leaves.

High temperatures and drought are expected to become more frequent in the future and last longer than ever before. To investigate their combined effect on cotton subtending leaves (LSCB), an experiment was conducted from 2016 to 2018 using a non-heat-tolerant cotton cultivar and a heat-tolerant cultivar. Two temperature regimes with ambient temperature (AT, 31.0/26.4 °C) and elevated temperature (ET, 33.4/28.9 °C, 2.5 °C higher than AT) and three drought treatments with a soil relative water content (SRWC) of 75 ± 5%, 60 ± 5%, and 45 ± 5% were established repeatedly. ET decreased Pn, initial rubisco activity (4.1.1.39, RuBP) and cy-FBPase (3.1.3.11) activity, upregulated GhSuSyA, and GhSuSyD expressions, and increased SuSy (2.4.1.13) activity, which led to the decline of the final starch and sucrose contents. Moreover, RuBP, Pn, and starch content all decreased with drop in SRWC levels, but the cy-FBPase and SPS (2.4.1.14) activity increased, which in turn increased sucrose content. Under combined stresses, when the changing trends of ET and drought effects were the same, the decrease of Pn, RuBP, and starch content was greater than under single stress exposure. However, when the changing trends of ET and drought effects were adverse, the combined effects on indicators such as cy-FBPase, SuSy, sucrose content were mostly similar to drought stress. These results indicate that the effect of drought on carbohydrate metabolism in LSCB is more prominent than ET. Thus, the drought effect for carbohydrate metabolism in LSCB may need more attention than ET under combined heat and drought stress. This article is protected by copyright. All rights reserved.

Optimized potassium application rate increases foxtail millet grain yield by improving photosynthetic carbohydrate metabolism.

Photosynthetic carbohydrate metabolism is an important biochemical process related to crop production and quality traits. Potassium (K) critically contributes to the process of photosynthetic carbon assimilation and carbohydrate metabolism. We explored the effects of potassium fertilization on physiological mechanisms including carbohydrate metabolism in foxtail millet and its yield. Field experiments were performed using two foxtail millet (Setaria italica L.) cultivars: 1) Jingu 21 (low-K sensitive); and 2) Zhangza 10 (low-K tolerant). Effect of five different potassium fertilizer (K2O) rates (0, 60, 120, 180, and 240 kg·hm-2) were tested in two consecutive years, 2020 and 2021. We found that potassium application significantly increases the K content, dry matter accumulation and yield. Jingu 21 and Zhangza 10 had maximum yields at 180 kg·hm-2 K application, which were 29.91% and 31.51% larger than without K application, respectively. Excessive K application (K240) did not further improve their yields. The suitable K fertilizer application of Jingu 21 and Zhangza 10 are 195.25-204.27 and 173.95-175.87 kg·K2O·hm-2, respectively. The net photosynthetic rate (Pn), ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco), phosphoenolpyruvate carboxylase (PEPC), and fructose-1,6-bisphosphatase (FBPase) were positively correlated with the potassium content. Potassium application improved the availability of carbon sources for carbohydrate synthesis. Compared with the K0 treatment, variations in the activities of sucrose phosphate synthase (SPS) and sucrose synthase (SuSy) in potassium-treated Jingu 21 (K60, K120, K180, and K240) were 17.94%-89.93% and 22.48%-182.10%, respectively, which were greater than those of Zhangza 10 (11.34%-71.12% and 16.18%-109.13%, respectively) and indicate that Jingu 21 is more sensitive to potassium application. The sucrose contents in the Jingu 21 and Zhangza 10 grains were 0.97%-1.15% and 1.04%-1.23%, respectively. The starch contents were 28.99%-37.75% and 24.81%-34.62%, respectively. The sucrose: ratio of Jingu 21 was smaller than that of Zhangza 10, indicating that Jingu 21 utilized nutrients better than Zhangza 10. Stepwise regression and path analysis showed that leaf and grain SuSy activity, by coordinating the source-sink relationship, have the greatest direct effect on Jingu 21 yield, whereas leaf SuSy activity, by promoting the generation of photosynthates at the source leaf, plays a leading role in Zhangza 10 yield increase. In conclusion, optimized K application can increase foxtail millet grain yield by improving photosynthesis and promoting carbohydrate accumulation and distribution.

Co-occurring elevated temperature and drought stresses during cotton fiber thickening stage inhibit fiber biomass accumulation and cellulose synthesis

In order to investigate the effect of simultaneous elevated temperature and drought on Gossypium hirsutum fiber development under the background of global climate change, cotton (cv. Sumian 15 and cv. PHY370WR) plants were grown under ambient temperature (AT) or elevated temperature (ET, 2.5–2.7 °C higher than AT) conditions from 2016 to 2018. Meanwhile, three soil relative water content (SRWC) levels including (75 ± 5) % (optimum soil moisture), (60 ± 5) % (moderate drought) and (45 ± 5) % (severe drought) were established under each temperature condition. Results showed that elevated temperature combined with drought more negatively impacted the theoretical maximum of fiber biomass by further reducing the duration of rapid increase and the average increase rate of fiber biomass than any single stress. Elevated temperature and drought had opposite effects on sucrose synthesis in fibers by differently altering sucrose phosphate synthase (SPS) activity and GhSPS isoforms (GhSPS-1, GhSPS-2, and GhSPS-3) expressions, and the two stresses had an antagonistic effect on SPS activity when they were coupled. However, lower sucrose content was observed under all single and coupled stresses, meaning that less carbon was available for cellulose synthesis. Elevated temperature or drought alone also limited cellulose synthesis by decreasing the activities of sucrose synthase (SuSy), soluble acid invertase (VIN) and alkaline invertase (CIN) involved in sucrose degradation. The decrease of SuSy activity should be the result of down-regulation of GhSuSyA, GhSuSyB and GhSuSyC expressions, and the decrease of VIN activity should be the result of down-regulation of GhInv-1 and GhInv-2 expressions under high temperature or drought alone. The combination of the two stresses had more negatively effects on SuSy activity by further down-regulating the iso-forms GhSuSyA and GhSuSyB expressions, on VIN activity by further decreasing GhInv-1 and GhInv-2 expressions, and on CIN activity than any single stress, which would further inhibit sucrose degradation to form UDPG for cellulose synthesis. Moreover, elevated temperature or drought alone enhanced callose accumulation by highly up-regulating GhCalS-5 expression and down-regulating β-1,3-glucanase expression, and the combined stress further increased the callose accumulation, suggesting that more UDPG from sucrose decomposition was allocated to callose synthesis rather than cellulose synthesis. All these confirmed that elevated temperature combined with drought exhibited synergistic negative effects on cotton fiber biomass accumulation and cellulose synthesis during fiber thickening.

An isoform of sucrose synthase involved in sink strength of potato (Solanum tuberosum L.): Molecular cloning, sequence analyses, 3-D structure, crucial motifs and expression

Sucrose synthase (SuSy, EC 2.4.1.13) refers to a glycosyltranferase (GT) that plays a crucial role in sugar metabolism mainly in the sink tissues of plants. Using uridine diphosphate (UDP) or adenosine diphosphate (ADP), SuSy catalyzes the reversible cleavage of sucrose into fructose, and UDP-glucose (UDP-Glc) or ADP-glucose (ADP-Glc), respectively. In plants, SuSy is encoded by relatively small gene families. It exists in multiple forms distributed differentially in the plant tissues suggesting their functional specializations. SuSy activity is regulated by a hierarchy of mechanisms including transcriptional control. Here, we report isolation and characterization of a 2,668-bp cDNA encoding a distinct full-length SuSy4 form, corresponding to SUS I group gene family, from a commercially important Indian potato (Solanum tuberosum L.) cultivar, Kufri Chipsona-1 by RT-PCR using tuber total RNA. The predicted protein consisted of 805 amino acids (designated KC-SuSy). All of the available potato SuSy proteins could be categorized into 3 groups i.e., SUS I−III as reported earlier in other plants. Phylogenetic analysis was carried out using the SuSy sequences from the potato, tomato and Arabidopsis. Multiple sequence alignments revealed segment-wise identity and divergence between the SuSy forms. Using KC-SuSy sequence, secondary structures, crucial domains/motifs and amino acids, and a three-dimensional (3-D) structure were predicted. KC-SuSy was found to be predominantly expressed in tuber. The early stages of tuber development were associated with high levels of SuSy activity. This report would be particularly useful for further studies on the SuSy proteins in potato and other Solanaceae family members.

The seed biochemical signature as a potent marker for water logging tolerance in maize

Plant breeders are in the need for convenient, reproducible, reliable and rapid screening methods to be used as a proxy for water logging tolerance for a large number of genotypes. Addressing this need, the present study was carried in order to identify potential biochemical markers in the seeds of 10 contrasting maize (Zea mays L.) genotypes differing in their tolerance against water logging. Results clearly indicate that tolerant genotypes inherently exhibit better antioxidant system as evident by higher activities of catalase and glutathione reductase than the susceptible genotypes hence minimizes resulting oxidative stress. Significantly higher activities of anaerobic metabolism enzymes viz. alcohol dehydrogenase, aldehyde dehydrogenase and pyruvate decarboxylase in tolerant maize genotypes signifies efficient system for the recycling of NADH for the continuation of glycolysis and simultaneous detoxification of acetaldehyde thus provides prolonged survival of tolerant plants under water logging. Higher Sucrose synthase (SuSy) activity in tolerant genotypes over the susceptible genotypes indicates uninterrupted supply of reducing sugars for glycolytic activity. The content of total and reducing sugars content was found 27% higher in tolerant genotypes, which is in agreement with the SuSy activity. Soluble sugars analysis through reverse phase HPLC revealed higher relative concentration of fructose and glucose in tolerant maize genotypes than susceptible genotypes. Tolerant genotypes also exhibited significantly lower phytic acid and higher proline content. Hence the observed biochemical diversity could be useful for screening and development of water logging stress-tolerant genotypes of maize.

Seed Germination and Seedling Growth of Dendrocalumus brandisii in vitro, and the Inhibitory Mechanism of Colchicine.

Bamboos seldom bloom and almost no seeds could be harvested, and, hence, few works are focused on germination physiology. Systematic research on the physiological effects of colchicine on germination and seedling growth of bamboo seeds is lacking. In this study, we finely recorded seed germination and seedling growth of Dendrocalamus brandisii in media supplemented with different colchicine concentrations. Physiological effects and mechanisms of colchicine were analyzed. The results showed that D. brandisii seeds were non-dormant, and seed lots achieved their highest germination rates on the 4th day and finished the whole germination period after 21 days. Colchicine inhibited seed germination and seedling growth but did not change its germination pattern. Seed germination and seedling growth decreased constantly with colchicine concentration. Colchicine showed more negative effects on seedling growth than on seed germination and root growth. High concentrations of colchicine retarded the development of plumules and even caused their aberrant development. Under tissue culture conditions, seed germination, and seedling growth relied mainly on the endogenous starch and soluble sugar degradation, in which α-amylase, STP, and SUSY played the key role. Colchicine inhibited seed germination and seedling growth by suppressing the α-amylase, STP, and SUSY activities. Colchicine showed more negative effects on sucrose degradation than on starch degradation during seed germination and seedling growth. This study provides new basic information on the seedling physiology for the genetic breeding of bamboo plants.

Sucrose-phosphate phosphatase from sugarcane reveals an ancestral tandem duplication

BackgroundSugarcane is capable to store large amounts of sucrose in the culm at maturity hence it became a major source of sucrose for the food and the renewable energy industries. Sucrose, the main disaccharide produced by photosynthesis, is mainly stored in the vacuole of the cells of non-photosynthetic tissues. Two pathways are known to release free sucrose in plant cells, one is de novo synthesis dependent on sucrose phosphate synthase (SPS) and sucrose phosphate phosphatase (S6PP) while the other is regulatory and dependent on sucrose synthase (SuSy) activity. The molecular understanding of genes that give rise to the expression of the enzyme sucrose phosphate phosphatase, responsible for the release of sucrose in the last synthetic step lag behind the regulatory SuSy gene.ResultsSugarcane genome sequencing effort disclosed the existence of a tandem duplication and the present work further support that both S6PP.1 and S6PP_2D isoforms are actively transcribed in young sugarcane plants but significantly less at maturity. Two commercial hybrids (SP80–3280 and R570) and both Saccharum spontaneum (IN84–58) and S.officinarum (BADILLA) exhibit transcriptional activity at three-month-old plants of the tandem S6PP_2D in leaves, culm, meristem and root system with a cultivar-specific distribution. Moreover, this tandem duplication is shared with other grasses and is ancestral in the group.ConclusionDetection of a new isoform of S6PP resulting from the translation of 14 exon-containing transcript (S6PP_2D) will contribute to the knowledge of sucrose metabolism in plants. In addition, expression varies along plant development and between sugarcane cultivars and parental species.

Physiological Traits for Shortening Crop Duration and Improving Productivity of Greengram (Vigna radiata L. Wilczek) Under High Temperature.

Greengram is an important protein-rich food legume crop. During the reproductive stage, high temperatures cause flower drop, induce male sterility, impair anthesis, and shortens the grain-filling period. Initially, 116 genotypes were evaluated for 3 years in two locations, and based on flowering, biomass, and yield attributes, they were grouped into four major clusters. A panel of 17 contrasting genotypes was selected for their heat tolerance in high-temperature greenhouses. The seedlings of the selected genotypes were exposed to heat shock in the range 37°C–52°C and their recovery after heat shock was assessed at 30°C. The seedlings of EC 398889 turned completely green and rejuvenated, while those of LGG 460 failed to recover, therefore, EC 398889 and LGG 460 were identified as heat-tolerant and heat-sensitive genotypes, respectively. Except for EC 398889, the remaining genotypes could not survive after heat shock. Fresh seeds of EC 398889 and LGG 460 were planted in field and pollen fertility and sucrose-synthase (SuSy) activity in grains were assessed at high temperatures. The pollen germination and SuSy activity were normal even at temperatures beyond 40°C in EC 398889 and high SuSy activity enabled faster grain filling than in LGG 460. The precise phenotyping demonstrated significant differences in the light-temperature response of photosynthesis, chlorophyll fluorescence imaging of quantum yield (Fv/Fm), and electron transport rate (ETR) between heat-tolerant (EC 398889) and heat-sensitive (LGG 460) genotypes. Molecular profiling of selected accessions showed polymorphism with 11 SSR markers and the markers CEDG147, CEDG247, and CEDG044 distinguished tolerant and sensitive groups of accessions.

Overexpression of PsnSuSy1, 2 genes enhances secondary cell wall thickening, vegetative growth, and mechanical strength in transgenic tobacco.

Two homologs PsnSuSy1 and PsnSuSy2 from poplar played largely similar but little distinct roles in modulating sink strength, accelerating vegetative growth and modifying secondary growth of plant. Co-overexpression of them together resulted in small but perceptible additive effects. Sucrose synthase (SuSy) acts as a crucial determinant of sink strength by controlling the conversion of sucrose into UDP-glucose, which is not only the sole precursor for cellulose biosynthesis but also an extracellular signaling molecule for plants growth. Therefore, modification of SuSy activity in plants is of utmost importance. We have isolated two SuSy genes from poplar, PsnSuSy1 and PsnSuSy2, which were preferentially expressed in secondary xylem/phloem. To investigate their functions, T2 tobacco transgenic lines of PsnSuSy1 and PsnSuSy2 were generated and then crossed to generate PsnSuSy1/PsnSuSy2 dual overexpression transgenic lines. SuSy activities in all lines were significantly increased though PsnSuSy1/PsnSuSy2 lines only exhibited slightly higher SuSy activities than either PsnSuSy1 or PsnSuSy2 lines. The significantly increased fructose and glucose, engendered by augmented SuSy activities, caused the alternations of many physiological, biochemical measures and phenotypic traits that include accelerated vegetative growth, thickened secondary cell wall, and increased stem breaking force, accompanied with altered expression levels of related pathway genes. The correlation relationships between SuSy activities and many of these traits were statistically significant. However, differences of almost all traits among three types of transgenic lines were insignificant. These findings clearly demonstrated that PsnSuSy1 and PsnSuSy2 had similar but little distinct functions and insubstantial additive effects on modulating sink strength and affecting allocation of carbon elements among secondary cell wall components.

Analysis of the diversity and tissue specificity of sucrose synthase genes in the long read transcriptome of sugarcane

BackgroundSugarcane accumulates very high levels of sucrose in the culm. Elucidation of the molecular mechanisms that allows such high sucrose synthesis and accumulation (up to 650 mM) is made difficult by the complexity of the highly polyploid genome. Here we report the use of RNA Seq data to characterize the sucrose synthase (SuSy) genes expressed in the transcriptome of the mature sugarcane plant.ResultsFour SuSy gene families were identified in the sugarcane Iso-Seq long read transcriptome (SUGIT) through gene annotation of transcripts that mapped to reference SuSy genes from sorghum and maize. In total, 38, 19, 14, and 2 transcripts were identified for the four corresponding SuSy genes 1, 2, 4 and 7, respectively. Comparative studies using available SuSy genes from sorghum (1, 2, 4, 6, 7) and maize (1–7) revealed that the sugarcane SuSy genes were interrupted by multiple introns and that they share a highly conserved gene structure. Spatial expression of the four SuSy genes in sugarcane genotypes and in the progenitor species, Saccharum spontaneum and Saccharum officinarum, was studied in the leaf and root tissues and also in three regions of the culm tissue; top, middle and bottom internodes. Expression profiles indicated that all SuSy transcripts were differentially expressed between the top and bottom tissues, with high expression in the top tissues, lower expression in the bottom and moderate expression in the middle, indicating a gradient of SuSy activity in the sugarcane culm. Further, the root tissue had similar expression levels to that of the top internodes while leaf tissues showed lower expression. In the progenitors, SuSy7 was found to be highly expressed in S. officinarum while the other three SuSy genes had moderate expression in both the progenitors.ConclusionsThe high expression of the SuSy genes in sink tissues, the top internodes and the roots suggests functional roles in sucrose utilization to support growth. The SuSy7 gene has not been previously reported in sugarcane. As sugarcane is unique in storing such high amounts of sucrose, it is possible that there are more SuSy genes/isoforms with specific expression patterns to be discovered in this complex system.

An Overview of Sucrose Synthases in Plants.

Sucrose is the end product of photosynthesis and the primary sugar transported in the phloem of most plants. Sucrose synthase (SuSy) is a glycosyl transferase enzyme that plays a key role in sugar metabolism, primarily in sink tissues. SuSy catalyzes the reversible cleavage of sucrose into fructose and either uridine diphosphate glucose (UDP-G) or adenosine diphosphate glucose (ADP-G). The products of sucrose cleavage by SuSy are available for many metabolic pathways, such as energy production, primary-metabolite production, and the synthesis of complex carbohydrates. SuSy proteins are usually homotetramers with an average monomeric molecular weight of about 90 kD (about 800 amino acids long). Plant SuSy isozymes are mainly located in the cytosol or adjacent to plasma membrane, but some SuSy proteins are found in the cell wall, vacuoles, and mitochondria. Plant SUS gene families are usually small, containing between four to seven genes, with distinct exon-intron structures. Plant SUS genes are divided into three separate clades, which are present in both monocots and dicots. A comprehensive phylogenetic analysis indicates that a first SUS duplication event may have occurred before the divergence of the gymnosperms and angiosperms and a second duplication event probably occurred in a common angiosperm ancestor, leading to the existence of all three clades in both monocots and dicots. Plants with reduced SuSy activity have been shown to have reduced growth, reduced starch, cellulose or callose synthesis, reduced tolerance to anaerobic-stress conditions and altered shoot apical meristem function and leaf morphology. Plants overexpressing SUS have shown increased growth, increased xylem area and xylem cell-wall width, and increased cellulose and starch contents, making SUS high-potential candidate genes for the improvement of agricultural traits in crop plants. This review summarizes the current knowledge regarding plant SuSy, including newly discovered possible developmental roles for SuSy in meristem functioning that involve sugar and hormonal signaling.

Sucrose Synthase (SuSy) Gene Expression: An Indicator for Cotton Fiber Initiation and Early Development

Cotton (Gossypium hirsutum L.) fiber initiation from ovule epidermal cells happen from 0 to 5 DPA, invertase (INV) and sucrose synthase (SuSy) are crucial for fiber initiation, cell expansion, and elongation. We used two commercial cotton varieties, Xuzhou 142-normal wild-type (WT) and Sea Island PimaS-4 (PimaS-4) as controls and compared with three fiber mutants, Xuzhou 142-fl (fl), Xuzhou 142-N (N) and Ligon lintless (Li). SuSy, INV activity, sugars and malate content were measured at fiber cell initiation and early development stage. Increased Susy activity was detected in WT, PimaS-4 and Li ovules at 0 DPA than the fiber mutant lines fl and N. On the other hand, fl mutant showed high sucrose contents than N and Li during 0 to 1 DPA. No significant changes happen in studied cotton lines with respect to INV from 1 to 5 DPA altogether. There was a significant difference in total soluble sugars and malate contents between WT and fl cotton ovules at early elongation stage (5 DPA). The results revealed that SuSy activity at anthesis day indicates the fate of ovule epidermal cells to bulge out and form fiber initials. The reduced SuSy activity in fl ovules at 0 DPA results in a lack of fiber cell initiation and lead to fiberless seed phenotype. The study will pave the way towards unraveling the mechanism of fiber initiation and development by exploring the role of different fiber-related genes.

Effects of potassium deficiency on the enzymatic changes in developing cotton fibers

Although effects of potassium (K) on cotton growth have been explored extensively, the effects of K deficiency on the physiological changes closely related to cotton fiber development are lacking. Thus, a 2-year field experiment was conducted with two cotton cultivars (Simian 3 and Siza 3) under 0 kg K2O ha−1 (K deficiency) and 300 kg K2O ha−1 (K sufficiency). The results showed that tonoplast adenosine triphosphatase (V-ATPase), pyrophosphatase (PPase), plasma membrane H+-ATPase (PM H+-ATPase), phosphoenolpyruvate carboxylase (PEPC), sucrose synthesis (SuSy) and vacuolar invertase (V-INV) were highly sensitive to K deficiency. The decreases in those enzymes resulted in low malate and soluble sugar contents, which together with low K concentration declined the driving force for fiber elongation, leading to significantly lower fiber length in the 0 kg K2O ha−1 treatment. The activity of sucrose phosphate synthase (SPS) was obviously increased by K deficiency before 20 days post anthesis (DPA), which could partly explain the acceleration of fiber cellulose synthesis and the increase in fiber strength in the 0 kg K2O ha−1 treatment in the early stage. However, SPS activity was decreased by K deficiency after 20 DPA and SuSy activity was reduced by K deficiency at any sampling date, resulting in low fiber strength in the end. Compared with Simian 3, the enzymes V-ATPase, PPase, PM H+-ATPase, PEPC and SuSy during fiber elongation stage were more sensitive to K deficiency in Siza 3, and the enzymes SuSy and SPS during fiber-thickening stage were more sensitive to K deficiency in Siza 3, which were the important reasons causing greater decreases in final fiber length and final fiber strength for Siza 3 than Simian 3 under K deficiency.

Changes in Soluble Sugar Accumulation and Activities of Sucrose-Metabolizing Enzymes during Fruit Ripening of Jackfruit

Jackfruit (Artocarpus heterophyllus Lam.) is an important food crop widely grown in the tropical region. However, little is known about sugar metabolism during fruit ripening of jackfruit. Here we examined sugar profiles (sucrose, glucose and fructose) and corresponding enzyme activities (SPS, E.C.2.4.1.14; SuSy, EC 2.4.1.13; IV, EC 3.2.1.26) of four soft type and four firm type varieties of jackfruit during four stages of fruit ripening. We found that during fruit ripening, there was a rapid increase in contents of total soluble sugar and sucrose, whereas increases in glucose and fructose contents were much slower. Ratios of glucose versus fructose varied among different varieties and ripening stages but within the range of 0.9 to 1.2 in the ripe fruits. Five of these varieties exhibited markedly high levels of SuSy activity for sucrose synthesis at early ripening stage, and then decreased towards fully ripe stage. All soft type varieties exhibited a conspicuous peak of AIV activity and had overall higher AIV activities than NIV during ripening. The changing patterns for other enzymes varied among varieties. Our studies support the notion that sucrose was the major sugar species contributing to the fruit sweetness, followed by fructose and glucose. We also demonstrated that AIV and NIV were probably the primary enzymes responsible for sucrose hydrolysis during ripening, while SPS and SuSy were responsible for sucrose synthesis. We propose that during fruit ripening of jackfruit, glucose is released from starch hydrolysis, followed by sucrose hydrolysis leading to increase in both glucose and fructose contents.

Carbohydrate metabolism in the subtending leaf cross-acclimates to waterlogging and elevated temperature stress and influences boll biomass in cotton (Gossypium hirsutum).

Short-term waterlogging and chronic elevated temperature occur concomitantly in the cotton (Gossypium hirsutum) growing season. While previous research about co-occurring waterlogging and elevated temperature has focused primarily on cotton fiber, no studies have investigated carbohydrate metabolism of the subtending leaf (a major source leaf for boll development) cross-acclimation to aforementioned stressors. To address this, plants were exposed to ambient (31.6/26.5°C) and elevated (34.1/29.0°C) temperatures during the whole flowering and boll formation stage, and waterlogging (0, 3, 6 days) beginning on the day of anthesis. Both waterlogging and high temperature limited boll biomass (reduced by 1.19-32.14%), but effects of different durations of waterlogging coupled with elevated temperature on carbohydrate metabolism in the subtending leaf were quite different. The 6-day waterlogging combined with elevated temperature had the most negative impact on net photosynthetic rate (Pn) and carbohydrate metabolism of any treatment, leading to upregulated GhSusA and GhSusC expression and enhanced sucrose synthase (SuSy, EC 2.4.1.13) activity for sucrose degradation. A prior exposure to waterlogging for 3 days improved subtending leaf performance under elevated temperature. Pn, sucrose concentrations, Rubisco (EC 4.1.1.39) activity, and cytosolic fructose-1,6-bisphosphatase (cy-FBPase, EC 3.1.3.11) activity in the subtending leaf significantly increased, while SuSy activity decreased under 3 days waterlogging and elevated temperature combined relative to elevated temperature alone. Thus, we concluded that previous exposure to a brief (3 days) waterlogging stress improved sucrose composition and accumulation cross-acclimation to high temperature later in development not only by promoting leaf photosynthesis but also inhibiting sucrose degradation.