Abscisic Acid Biosynthesis Pathway Research Articles

RNA splicing modulates the postharvest physiological deterioration of cassava storage root.

Rapid postharvest physiological deterioration (PPD) of cassava (Manihot esculenta Crantz) storage roots is a major constraint that limits the potential of this plant as a food and industrial crop. Extensive studies have been performed to explore the regulatory mechanisms underlying the PPD processes in cassava to understand their molecular and physiological responses. However, the exceptional functional versatility of alternative splicing (AS) remains to be explored during the PPD process in cassava. Here, we identified several aberrantly spliced genes during the early PPD stage. An in-depth analysis of AS revealed that the abscisic acid (ABA) biosynthesis pathway might serve as an additional molecular layer in attenuating the onset of PPD. Exogenous ABA application alleviated PPD symptoms through maintaining ROS generation and scavenging. Interestingly, the intron retention transcript of MeABA1 (ABA DEFICIENT 1) was highly correlated with PPD symptoms in cassava storage roots. RNA yeast three-hybrid and RNA immunoprecipitation assays showed that the serine/arginine-rich protein MeSCL33 (SC35-like splicing factor 33) binds to the precursor mRNA of MeABA1. Importantly, overexpressing MeSCL33 in cassava conferred improved PPD resistance by manipulating the AS and expression levels of MeABA1 and then modulating the endogenous ABA levels in cassava storage roots. Our results uncovered the pivotal role of the ABA biosynthesis pathway and RNA splicing in regulating cassava PPD resistance and proposed the essential roles of MeSCL33 for conferring PPD resistance, broadening our understanding of SR proteins in cassava development and stress responses.

Expression pattern of candidate genes and their correlation with various metabolites of abscisic acid biosynthetic pathway under drought stress in rice

AbstractDrought hampers global rice production. Abscisic acid (ABA) plays versatile roles under different environmental stresses. While the link between drought and ABA is known, its effect on ABA biosynthesis genes and metabolites is unclear. This study explored the impact of drought on various metabolites, namely beta‐carotene, zeaxanthin, antheraxanthin, violaxanthin, neoxanthin, and candidate genes viz. zeaxanthin epoxidase (ZEP) and 9‐cis epoxycarotenoid dioxygenase (NCED) of ABA biosynthesis pathway in rice cultivars (N22 and IR64) at anthesis {65 DAT (Days after transplanting)} with different stress levels. In stressed plants, zeaxanthin significantly increased (92%), while the concentration of beta‐carotene, antheraxanthin, violaxanthin and neoxanthin decreased as drought stress progressed. The concentration of metabolites in roots was notably lower than in leaves in both genotypes. The ZEP expression was upregulated in roots (8.24‐fold) under drought stress. Among five NCED isoforms, NCED3 showed significant upregulation (7.29‐fold) in leaf and root tissue. NCED1 was significantly downregulated as stress progressed and was negatively correlated with ABA accumulation. NCED2, NCED4 and NCED5 showed no significant change in their expression. Drying and rolling of rice leaves was observed after imparting drought stress. The findings revealed that drought stress significantly influenced the expression of candidate genes and the concentration of metabolites of the ABA biosynthesis pathway. There was a significantly higher accumulation of ABA in N22 leaves (47%) and roots (30%) compared to IR64. The N22, a drought‐tolerant genotype, exhibited significantly higher concentrations of intermediates and demonstrated increased expression of ZEP and NCED3, potentially contributing to its resilience against drought.

Allantoin improves salinity tolerance in Arabidopsis and rice through synergid activation of abscisic acid and brassinosteroid biosynthesis.

Soil salinity stress is one of the major bottlenecks for crop production. Although, allantoin is known to be involved in nitrogen metabolism in plants, yet several reports in recent time indicate its involvement in various abiotic stress responses including salinity stress. However, the detail mechanism of allantoin involvement in salinity stress tolerance in plants is not studied well. Moreover, we demonstrated the role of exogenous application of allantoin as well as increased concentration of endogenous allantoin in rendering salinity tolerance in rice and Arabidopsis respectively, via., induction of abscisic acid (ABA) and brassinosteroid (BR) biosynthesis pathways. Exogenous application of allantoin (10µM) provides salt-tolerance to salt-sensitive rice genotype (IR-29). Transcriptomic data after exogenous supplementation of allantoin under salinity stress showed induction of ABA (OsNCED1) and BR (Oscytochrome P450) biosynthesis genes in IR-29. Further, the key gene of allantoin biosynthesis pathway i.e., urate oxidase of the halophytic species Oryza coarctata was also found to induce ABA and BR biosynthesis genes when over-expressed in transgenic Arabidopsis. Thus, indicating that ABA and BR biosynthesis pathways were involved in allantoin mediated salinity tolerance in both rice and Arabidopsis. Additionally, it has been found that several physio-chemical parameters such as biomass, Na+/K+ ratio, MDA, soluble sugar, proline, allantoin and chlorophyll contents were also associated with the allantoin-mediated salinity tolerance in urate oxidase overexpressed lines of Arabidopsis. These findings depicted the functional conservation of allantoin for salinity tolerance in both plant clades.

Elucidating Biological Functions of 9-cis-Epoxycarotenoid Dioxygenase Genes Involved in Seed Dormancy in Paeonia lactiflora

Abscisic acid (ABA) is a major phytohormone affecting seed dormancy and germination in plants. ABA is synthesized mainly through the C40 carotenoid pathway. In the ABA biosynthesis pathway, 9-cis-epoxycarotenoid dioxygenase (NCED) is a key rate-limiting enzyme that regulates the accumulation and content of ABA. However, the role of the NCED gene in perennial plants with complex seed dormancy remains largely unknown. Here, we cloned two differentially expressed paralogs of herbaceous peony NCED genes, named PlNCED1 and PlNCED2, and further identified their involvement in seed dormancy from perennial herbaceous peony experiencing complex double seed dormancy. The deduced PlNCED amino acid sequences had high sequence homology with NCED sequences from other plants and contained the typical conserved RPE65 domain of the NCED family. Phylogenetic analysis showed that PlNCED1 and PlNCED2 have a close relationship with PoNCED in Paeonia ostii and VvNCED6 in Vitis vinifera, respectively. A subcellular localization assay demonstrated that the PlNCED1 protein resided within the nucleus, while the PlNCED2 protein was located in the cytoplasm, indicating their different roles in the biosynthesis of ABA. Furthermore, the content of endogenous ABA in transgenic calluses showed that PlNCEDs were positively correlated with ABA content. Both PlNCED transgenic Arabidopsis lines and the functional complementation of Arabidopsis NCED mutants found that PlNCEDs promoted seed dormancy and delayed seed germination. These results reveal that PlNCEDs participate in the seed dormancy of herbaceous peony by regulating the accumulation of endogenous ABA.

Transcriptome Analysis of ‘Kyoho’ Grapevine Leaves Identifies Heat Response Genes Involved in the Transcriptional Regulation of Photosynthesis and Abscisic Acid

Grapevine is a popular cultivated fruit throughout the world and heat stress is one of the most serious threats to viticulture. However, transcriptional responses, such as molecular properties of photosynthesis and abscisic acid biosynthesis, metabolism and signal transduction pathway of grapevine to heat stress, are still poorly understood. In this study, RNA-seq was carried out for thermostabilized grapevine ‘Kyoho’ leaves. Results showed that 685 and 469 genes were commonly down-regulated and up-regulated at three sampling time-points. The light-dependent reactions of photosynthesis was significantly enriched in up-regulated DEGs at 1 hpt and down-regulated DEGs at R24 hpt. Heat stress impaired the photosynthetic capacity of grapevine leaves, and there was a significant positive relationship between photosynthesis and stomatal conductance at short-term post-heat stress treatment, but the inhibition of HS on Pn was non-stomata limitation for a longer period. Photosystem (PS)Ⅱ was more sensitive to heat stress than PSⅠ, and PsbP, as well as Psb28, played important roles in response to heat stress. The abscisic acid (ABA) content in heat-stress-treated Kyoho plants was higher than that in the control at 1 hpt, but less in heat-stress-treated plants at 4 and R24 hpt, which was regulated by numerous genes involved in the ABA biosynthesis and catabolism pathways. These results help to understand the influence of heat stress on photosynthesis and ABA biosynthesis, metabolism and signal transduction pathway.

Abscisic Acid: Role in Fruit Development and Ripening.

Abscisic acid (ABA) is a plant growth regulator known for its functions, especially in seed maturation, seed dormancy, adaptive responses to biotic and abiotic stresses, and leaf and bud abscission. ABA activity is governed by multiple regulatory pathways that control ABA biosynthesis, signal transduction, and transport. The transport of the ABA signaling molecule occurs from the shoot (site of synthesis) to the fruit (site of action), where ABA receptors decode information as fruit maturation begins and is significantly promoted. The maximum amount of ABA is exported by the phloem from developing fruits during seed formation and initiation of fruit expansion. In the later stages of fruit ripening, ABA export from the phloem decreases significantly, leading to an accumulation of ABA in ripening fruit. Fruit growth, ripening, and senescence are under the control of ABA, and the mechanisms governing these processes are still unfolding. During the fruit ripening phase, interactions between ABA and ethylene are found in both climacteric and non-climacteric fruits. It is clear that ABA regulates ethylene biosynthesis and signaling during fruit ripening, but the molecular mechanism controlling the interaction between ABA and ethylene has not yet been discovered. The effects of ABA and ethylene on fruit ripening are synergistic, and the interaction of ABA with other plant hormones is an essential determinant of fruit growth and ripening. Reaction and biosynthetic mechanisms, signal transduction, and recognition of ABA receptors in fruits need to be elucidated by a more thorough study to understand the role of ABA in fruit ripening. Genetic modifications of ABA signaling can be used in commercial applications to increase fruit yield and quality. This review discusses the mechanism of ABA biosynthesis, its translocation, and signaling pathways, as well as the recent findings on ABA function in fruit development and ripening.

The phytomelatonin receptor PMTR1 regulates seed development and germination by modulating abscisic acid homeostasis in Arabidopsis thaliana.

Melatonin is known to involve multiple physiological actions in plants. Herein, we found that exogenous melatonin inhibited the Arabidopsis seedling growth through the elevated abscisic acid (ABA) levels, and the elevated ABA was ascribed to the upregulation of 9-cis-epoxycarotenoid dioxygenase genes (NCEDs) in the ABA biosynthesis pathway. We also found that the overexpression lines of the melatonin receptor gene PMTR1 (also known as Cand2) yielded smaller seeds and germinated slower than the wild type, whereas PMTR1-knockout mutants produced larger seeds and germinated faster than the wild type. During the seed development, the accumulation peak of ABA was higher in the PMTR1-knockout mutant, while it was lower in the PMTR1-overexpression line than that in the wild type. In the dry seeds and imbibed seeds, the PMTR1-overexpression line accumulated higher ABA levels, while the PMTR1-knockout contained less ABA than the wild type. In summary, our findings suggest that PMTR1 is involved in ABA-mediated seed development and germination in Arabidopsis.

A unique miR775-GALT9 module regulates leaf senescence in Arabidopsis during post-submergence recovery by modulating ethylene and the abscisic acid pathway.

The submergence-induced hypoxic condition negatively affects the plant growth and development, and causes early onset of senescence. Hypoxia alters the expression of a number of microRNAs (miRNAs). However, the molecular function of submergence stress-induced miRNAs in physiological or developmental changes and recovery remains poorly understood. Here, we show that miR775 is an Arabidopsis thaliana-specific young and unique miRNA that possibly evolved non-canonically. miR775 post-transcriptionally regulates GALACTOSYLTRANSFERASE 9 (GALT9) and their expression is inversely affected at 24 h of complete submergence stress. The overexpression of miR775 (miR775-Oe) confers enhanced recovery from submergence stress and reduced accumulation of RBOHD and ROS, in contrast to wild-type and MIM775 Arabidopsis shoot. A similar recovery phenotype in the galt9 mutant indicates the role of the miR775-GALT9 module in post-submergence recovery. We predicted that Golgi-localized GALT9 is potentially involved in protein glycosylation. The altered expression of senescence-associated genes (SAG12, SAG29 and ORE1), ethylene signalling (EIN2 and EIN3) and abscisic acid (ABA) biosynthesis (NCED3) pathway genes occurs in miR775-Oe, galt9 and MIM775 plants. Thus, our results indicate the role for the miR775-GALT9 module in post-submergence recovery through a crosstalk between the ethylene signalling and ABA biosynthesis pathways.

Effects of root restriction on phytohormone levels in different growth stages and grapevine organs

Phytohormones play important roles in germination, blossom, senescence, abscission of plants by a series of signal transduction and molecular regulation. The purpose of this research was to investigate the influence of root restriction (RR) cultivation on plant endogenous hormone variation tendency at different growth stages in diverse organs or tissues. ‘Muscat Hamburg’ (Vitis ‘Muscat of Alexandria’ × Vitis ‘Trollinger’) grapevine was used as test material. High Performance Liquid Chromatography (HPLC) was used to quantify hormone levels, qRT-PCR was used to quantify the expression of genes related to hormone biosynthesis pathway, and determined parameters of growth and photosynthetic, aiming to investigate the influence of root restriction on the formation and metabolism of phytohormones, as well as the degree of correlation between phytohormones and plant growth and photosynthetic intensity under root restriction. By measuring the photosynthetic rate of leaves at the stages of core-hardening, veraison and maturity, it was found that root restriction could reduce most photosynthetic parameters. The results also revealed that RR treatment increased abscisic acid (ABA), salicylic acid (SA), zeatin riboside (ZR), N6-(delta 2-isopentenyl)-adenine nucleoside (iPR) concentrations, while reduced auxin (IAA), 3-indolepropionic acid (IPA), 3-indolebutyric acid (IBA), gibberellin A3 (GA3), zeatin (ZT), N6-(delta 2-Isopentenyl)-adenine (iP), kinetin (KT), jasmonic acid (JA) and methyl jasmonate (MeJA) concentrations in most organs and at most developmental stages. RT-qPCR was carried out to further explore the effect of root restriction on genes expression of ABA, SA and IAA biosynthesis pathways at molecular level. Meanwhile, through correlation analysis, we found that different phytohormones contributed differently to physiological indicators, there existed strong correlation of ABA, KT, MeJA, iPR, SA, JA with leaf photosynthesis, GA3, IBA, ZR, IAA, ZT with fruit quality. In addition, we also found that the shoot growth related parameters were closely correlated with JA, IPA and iP. To sum up, our results suggested that RR treatment could significantly increase soluble solid content, regulate the growth and photosynthesis of grapevine, by affecting the biosynthesis of phytohormones. It could further prove that root restriction was a feasible technique to ameliorate the phenomenon of low quality in grape berry in southern China.

Molecular mechanism of mulberry response to drought stress revealed by complementary transcriptomic and iTRAQ analyses

BackgroundThe use of mulberry leaves has long been limited to raising silkworms, but with the continuous improvement of mulberry (Morus alba) resource development and utilization, various mulberry leaf extension products have emerged. However, the fresh leaves of mulberry trees have a specific window of time for picking and are susceptible to adverse factors, such as drought stress. Therefore, exploring the molecular mechanism by which mulberry trees resist drought stress and clarifying the regulatory network of the mulberry drought response is the focus of the current work.ResultsIn this study, natural and drought-treated mulberry grafted seedlings were used for transcriptomic and proteomic analyses (CK vs. DS9), aiming to clarify the molecular mechanism of the mulberry drought stress response. Through transcriptome and proteome sequencing, we identified 9889 DEGs and 1893 DEPs enriched in stress-responsive GO functional categories, such as signal transducer activity, antioxidant activity, and transcription regulator activity. KEGG enrichment analysis showed that a large number of codifferentially expressed genes were enriched in flavonoid biosynthesis pathways, hormone signalling pathways, lignin metabolism and other pathways. Through subsequent cooperation analysis, we identified 818 codifferentially expressed genes in the CK vs. DS9 comparison group, including peroxidase (POD), superoxide dismutase (SOD), aldehyde dehydrogenase (ALDHs), glutathione s-transferase (GST) and other genes closely related to the stress response. In addition, we determined that the mulberry gene MaWRKYIII8 (XP_010104968.1) underwent drought- and abscisic acid (ABA)-induced expression, indicating that it may play an important role in the mulberry response to drought stress.ConclusionsOur research shows that mulberry can activate proline and ABA biosynthesis pathways and produce a large amount of proline and ABA, which improves the drought resistance of mulberry. MaWRKYIII8 was up-regulated and induced by drought and exogenous ABA, indicating that MaWRKYIII8 may be involved in the mulberry response to drought stress. These studies will help us to analyse the molecular mechanism underlying mulberry drought tolerance and provide important gene information and a theoretical basis for improving mulberry drought tolerance through molecular breeding in the future.

OsIAA18, an Aux/IAA Transcription Factor Gene, Is Involved in Salt and Drought Tolerance in Rice.

Auxin/indoleacetic acid (Aux/IAA) proteins play an important regulatory role in the developmental process of plants and their responses to stresses. A previous study has shown that constitutive expression of OsIAA18, an Aux/IAA transcription factor gene of rice improved salt and osmotic tolerance in transgenic Arabidopsis plants. However, little work is known about the regulatory functions of the OsIAA18 gene in regulating the abiotic stress tolerance of rice. In this study, the OsIAA18 gene was introduced into the rice cultivar, Zhonghua 11 and the OsIAA18 overexpression in rice plants exhibited significantly enhanced salt and drought tolerance compared to the wild type (WT). Moreover, overexpression of OsIAA18 in rice increased endogenous levels of abscisic acid (ABA) and the overexpression of OsIAA18 in rice plants showed hypersensitivity to exogenous ABA treatment at both the germination and postgermination stages compared to WT. Overexpression of OsIAA18 upregulated the genes involved in ABA biosynthesis and signaling pathways, proline biosynthesis pathway, and reactive oxygen species (ROS)-scavenging system in the overexpression of OsIAA18 in rice plants under salt and drought stresses. Proline content, superoxide dismutase (SOD), and peroxidase (POD) activities were significantly increased, whereas malonaldehyde (MDA), hydrogen peroxide (H2O2), and superoxide anion radical (O2–) content were significantly decreased in the transgenic plants under salt and drought stresses. Taken together, we suggest that OsIAA18 plays a positive role in drought and salt tolerance by regulating stress-induced ABA signaling. The OsIAA18 gene has a potential application in genetically modified crops with enhanced tolerance to abiotic stresses.

Transcriptomic Analysis Reveals the Positive Role of Abscisic Acid in Endodormancy Maintenance of Leaf Buds of Magnolia wufengensis.

Magnolia wufengensis (Magnoliaceae) is a deciduous landscape species, known for its ornamental value with uniquely shaped and coloured tepals. The species has been introduced to many cities in south China, but low temperatures limit the expansion of this species in cold regions. Bud dormancy is critical for plants to survive in cold environments during the winter. In this study, we performed transcriptomic analysis of leaf buds using RNA sequencing and compared their gene expression during endodormancy, endodormancy release, and ecodormancy. A total of 187,406 unigenes were generated with an average length of 621.82 bp (N50 = 895 bp). In the transcriptomic analysis, differentially expressed genes involved in metabolism and signal transduction of hormones especially abscisic acid (ABA) were substantially annotated during dormancy transition. Our results showed that ABA at a concentration of 100 μM promoted dormancy maintenance in buds of M. wufengensis. Furthermore, the expression of genes related to ABA biosynthesis, catabolism, and signalling pathway was analysed by qPCR. We found that the expression of MwCYP707A-1-2 was consistent with ABA content and the dormancy transition phase, indicating that MwCYP707A-1-2 played a role in endodormancy release. In addition, the upregulation of MwCBF1 during dormancy release highlighted the enhancement of cold resistance. This study provides new insights into the cold tolerance of M. wufengensis in the winter from bud dormancy based on RNA-sequencing and offers fundamental data for further research on breeding improvement of M. wufengensis.

Different abscisic acid‐deficient mutants show unique morphological and hydraulic responses to high air humidity

High relative humidity (RH) perturbs plant growth, stomatal functioning and abscisic acid (ABA) homeostasis, but the role of ABA in this physiological regulation is equivocal. To determine the role(s) of ABA in plant responses to high RH, wild-type (WT) tomato and barley plants and their respective ABA-deficient mutants flacca and Az34 (which are mutated in the same locus of the ABA biosynthesis pathway) were grown in contrasting RHs (60% and 90%) to measure biomass partitioning, stomatal traits and water relations. Surprisingly, growth RH did not affect foliar ABA levels in either species. While Az34 showed similar stomatal size and density as WT plants, flacca had larger and more abundant stomata. High RH increased stomatal size in tomato, but decreased it in barley, and decreased stomatal density in tomato, but not in barley. Altered stomatal responses in ABA-deficient plants to high RH had little effect on tomato photosynthesis, but Az34 barley showed lower photosynthesis. ABA deficiency decreased relative shoot growth rate (RGRSHOOT ) in both species, yet this was counteracted by high RH increasing leaf water status in tomato, but not in barley. High RH increased RGRSHOOT in flacca, but not in WT tomatoes, while having no effect on RGRSHOOT in barley, but affecting barley net assimilation rate, leaf area ratio (LAR) and specific leaf area in an ABA-dependent manner. ABA-RH interaction affected leaf development in tomato only. Thus, different crop species show variable responses to both high RH and ABA deficiency, making it difficult to generalise on the role of ABA in growth regulation at contrasting RHs.

Myb10-D confers PHS-3D resistance to pre-harvest sprouting by regulating NCED in ABA biosynthesis pathway of wheat.

Summary Pre‐harvest sprouting (PHS), the germination of grain before harvest, is a serious problem resulting in wheat yield and quality losses.Here, we mapped the PHS resistance gene PHS‐3D from synthetic hexaploid wheat to a 2.4 Mb presence–absence variation (PAV) region and found that its resistance effect was attributed to the pleiotropic Myb10‐D by integrated omics and functional analyses.Three haplotypes were detected in this PAV region among 262 worldwide wheat lines and 16 Aegilops tauschii, and the germination percentages of wheat lines containing Myb10‐D was approximately 40% lower than that of the other lines. Transcriptome and metabolome profiling indicated that Myb10‐D affected the transcription of genes in both the flavonoid and abscisic acid (ABA) biosynthesis pathways, which resulted in increases in flavonoids and ABA in transgenic wheat lines. Myb10‐D activates 9‐cis‐epoxycarotenoid dioxygenase (NCED) by biding the secondary wall MYB‐responsive element (SMRE) to promote ABA biosynthesis in early wheat seed development stages.We revealed that the newly discovered function of Myb10‐D confers PHS resistance by enhancing ABA biosynthesis to delay germination in wheat. The PAV harboring Myb10‐D associated with grain color and PHS will be useful for understanding and selecting white grained PHS resistant wheat cultivars.

Melatonin Pretreatment Confers Heat Tolerance and Repression of Heat-Induced Senescence in Tomato Through the Modulation of ABA- and GA-Mediated Pathways.

Heat stress and abscisic acid (ABA) induce leaf senescence, whereas melatonin (MT) and gibberellins (GA) play critical roles in inhibiting leaf senescence. Recent research findings confirm that plant tolerance to diverse stresses is closely associated with foliage lifespan. However, the molecular mechanism underlying the signaling interaction of MT with GA and ABA regarding heat-induced leaf senescence largely remains undetermined. Herein, we investigated putative functions of melatonin in suppressing heat-induced leaf senescence in tomato and how ABA and GA coordinate with each other in the presence of MT. Tomato seedlings were pretreated with 100 μM MT or water and exposed to high temperature (38/28°C) for 5 days (d). Heat stress significantly accelerated senescence, damage to the photosystem and upregulation of reactive oxygen species (ROS), generating RBOH gene expression. Melatonin treatment markedly attenuated heat-induced leaf senescence, as reflected by reduced leaf yellowing, an increased Fv/Fm ratio, and reduced ROS production. The Rbohs gene, chlorophyll catabolic genes, and senescence-associated gene expression levels were significantly suppressed by MT addition. Exogenous application of MT elevated the endogenous MT and GA contents but reduced the ABA content in high-temperature-exposed plants. However, the GA and ABA contents were inhibited by paclobutrazol (PCB, a GA biosynthesis inhibitor) and sodium tungstate (ST, an ABA biosynthesis inhibitor) treatment. MT-induced heat tolerance was compromised in both inhibitor-treated plants. The transcript abundance of ABA biosynthesis and signaling genes was repressed; however, the biosynthesis genes MT and GA were upregulated in MT-treated plants. Moreover, GA signaling suppressor and catabolic gene expression was inhibited, while ABA catabolic gene expression was upregulated by MT application. Taken together, MT-mediated suppression of heat-induced leaf senescence has collaborated with the activation of MT and GA biosynthesis and inhibition of ABA biosynthesis pathways in tomato.

GhANN1 modulates the salinity tolerance by regulating ABA biosynthesis, ion homeostasis and phenylpropanoid pathway in cotton

Soil salinity is a major environmental stressor and seriously affects cotton yield and quality. ANNEXINs (ANNs) are a family of calcium-dependent membrane binding proteins, which function in many cellular processes. In this study, we found that GhANN1 (GenBank Accession No: KM062523), encoding an annexin protein in cotton, was strongly upregulated by phytohormone abscisic acid (ABA) and salt stress treatments. Overexpressing GhANN1 improved cotton tolerance to salinity stress, in which GhANN1 regulated ABA and phenylpropanoid biosynthesis pathways and increased the expression of Na+, K+ transporter-related genes in cotton roots. Additionally, transcriptional repressor GhWRKY40-like was involved in ABA-dependent pathway, which could bind directly to the GhANN1 promoter to form a novel GhANN1-ABA-GhWRKY40-like loop and fine-tune cotton response to salt stress. This study reveals the function of GhANN1 in enhancing cotton salt tolerance by regulating ABA accumulation, coordinating ion homeostasis, and participating in phenylpropanoid biosynthesis pathway, which will deepen our insight into plant response to abiotic stresses and provide valuable gene resources for cotton salt-tolerant breeding.

A novel wheat ASR gene, TaASR2D, enhances drought tolerance in Brachypodium distachyon

Abscisic acid-, stress-, and ripening-induced (ASR) proteins play an important role in protecting plants against adverse environmental conditions. Here, we identified 24 ASR genes in the wheat genome and analyzed their characteristics. Among these, five ASR genes highly induced by abscisic acid (ABA) and polyethylene glycol were cloned and further characterized. The TaASR genes were expressed in response to different abiotic stresses and ABA and were found to be localized in the nucleus and plasma membrane of transformed tobacco cells. Brachypodium distachyon transgenic plants overexpressing TaASR2D showed enhanced drought tolerance by regulating leaf transpiration. The expression levels of stress-related and ABA-responsive genes were higher in transgenic plants than in wild-type plants under drought stress conditions. Moreover, overexpression of TaASR2D increased the levels of both endogenous ABA and hydrogen peroxide in response to drought stress, and these plants showed hypersensitivity to exogenous ABA at the germination stage. Furthermore, plants overexpressing TaASR2D showed increased stomatal closure. Further analysis revealed that TaASR2D interacts with ABA biosynthesis and stress-related proteins in yeast and tobacco plants. Collectively, these findings indicate that TaASR2D plays an important role in the response of plants to drought stress by regulating the ABA biosynthesis pathway and redox homeostasis system.

Comparative transcriptome analyses provide novel insights into etiolated shoot development of walnut (Juglans regia L.).

In general, genes promoting IAA, CTK GA and ethylene biosynthesis were upregulated, while genes participating in ABA, chlorophyll and starch biosynthesis pathways performed opposite tendency during etiolation. Etiolation as a method for rejuvenation plays an important role in the vegetative propagation of woody plants. However, the molecular mechanism of etiolated shoot development remains unclear. In this study, we investigated changes at different etiolation stages of Juglans regia. The histology and transcriptome of J. regia were analysed using etiolated stems, which were treated in darkness for 30, 60, 90days. The results showed that the ratios of pith (Pi) diameter/stem diameter (D), cortex (Co) width/D, and phloem (Ph) width/D increased, while the ratio of xylem (Xy) width/D decreased after etiolation, and the difference in these ratios between etiolated stems and the control was more significant at 60 days than 90 days. Differentially expressed genes (DEGs) were significantly enriched in pathways such as plant hormone biosynthesis and signal transduction, chlorophyll biosynthesis and degradation, and starch and sucrose metabolism. The difference in the contents of indole-3-acetic acid (IAA), abscisic acid (ABA), sugar and chlorophyll between etiolated stems and the control increased with increasing treatment duration; in contrast, the concentrations of gibberellin (GA), zeatin (ZT), and starch, as well as the difference between the etiolated stems and control were lowest at 60 days among the three stages. On the whole, the positive effect of etiolation on the rejuvenation of walnut stems changed as the treatment period increased. The present investigation lays a foundation for future studies on the effect of etiolation on rejuvenation and for promoting the efficiency of vegetative propagation.

Early ABA-stimulated maintenance of Cl− homeostasis by mepiquat chloride priming confers salt tolerance in cotton seeds

Mepiquat chloride (MC) priming alleviates the effects of salt stress during seed germination in cotton (Gossypium hirsutum L.), but the mechanisms underlying its effects are unknown. We found that MC priming increases salt tolerance, as evidenced by marked increases in seed vigor and germination rates, and alleviated salt toxicity by reducing Cl− accumulation in germinating seeds. Consistently, electrophysiological experiments revealed that the seeds with MC priming displayed superior Cl− exclusion ability in the root apex. These beneficial effects of MC priming were abolished by the abscisic acid (ABA)-synthesis blocker fluridone under salt stress. MC priming induced an early response to acclimatization and stress, as indicated by rapidly increasing ABA content during initial exposure to salt stress. Transcriptome analyses revealed that MC priming induced an array of differentially expressed genes (DEGs) in germinating seeds. The most noticeable changes in germinating seeds were MC priming-induced increases in the expression of DEGs encoding components of ABA biosynthesis, ABA catabolism, and ABA signaling pathways under salt stress. MC priming also increased the expression of some DEGs encoding Cl− ion transporters (e.g. CCC, SLAC1/SLAH1/SLAH3, CLC, and ALMT9) in germinating seeds. These results indicate that MC priming-induced ABA contributes to Cl− homeostasis in tissues and acts as a positive regulator of salt tolerance via regulation of Cl− transporters (particularly CCC and SLAC1/SLAH1/SLAH3). Taken together, these findings shed light on the molecular mechanism underlying MC-mediated tolerance to salt stress during seed germination.

Implications of Abscisic Acid in the Drought Stress Tolerance of Plants

Drought is a severe environmental constraint, which significantly affects plant growth, productivity, and quality. Plants have developed specific mechanisms that perceive the stress signals and respond to external environmental changes via different mitigation strategies. Abscisic acid (ABA), being one of the phytohormones, serves as an important signaling mediator for plants’ adaptive response to a variety of environmental stresses. ABA triggers many physiological processes, including bud dormancy, seed germination, stomatal closure, and transcriptional and post-transcriptional regulation of stress-responsive gene expression. The site of its biosynthesis and action must be clarified to understand the signaling network of ABA. Various studies have documented multiple sites for ABA biosynthesis, their transporter proteins in the plasma membrane, and several components of ABA-dependent signaling pathways, suggesting that the ABA response to external stresses is a complex networking mechanism. Knowing about stress signals and responses will increase our ability to enhance crop stress tolerance through the use of various advanced techniques. This review will elaborate on the ABA biosynthesis, transportation, and signaling pathways at the molecular level in response to drought stress, which will add a new insight for future studies.