Tolerance To Chilling Stress Research Articles

Physiological and proteomic analyses reveals that brassinosteroids application improves the chilling stress tolerance of pepper seedlings

Brassinosteroids (BRs) are important in plant resistance to chilling stress. However, limited information is available regarding the specific mechanisms involved at proteomic level. We utilized the iTRAQ proteomic approach, physiological assays and information obtained from cellular ultrastructure to clarify the underlying molecular mechanism of BRs to alleviate chilling stress in pepper (Capsicum annuum L.). Foliar application of 24-epibrassinolide (EBR) improved photosynthesis and improved cell structure by presenting a distinct mesophyll cell and chloroplast with well-developed thylakoid membranes in the leaves of pepper seedlings. We identified 346 differentially expressed proteins (DEPs), including 217 up-regulated proteins and 129 down-regulated proteins in plants under chilling (Chill) and Chill + EBR treated plants. Most of the DEPs were related to multiple pathways, including photosynthesis, carbohydrate metabolism, energy metabolism, protein biosynthesis, amino acid synthesis, redox and stress defence (ascorbate peroxidase, glutathione peroxidase and superoxide dismutase). Up-regulated DEPs were associated with the photosynthetic electron transfer chain, oxidative phosphorylation, GSH metabolism pathway, Calvin cycle and signaling pathway. The physiochemical analysis showed that EBR treatment improved the tolerance of pepper seedlings to chilling stress.

Ferulic acid enhances chilling tolerance in tomato fruit by up-regulating the gene expression of CBF transcriptional pathway in MAPK3-dependent manner

Ferulic acid (FA, 4-hydroxy-3-methoxycinnamic acid) is a phenolic acid derivative of cinnamic acid and plays pleiotropic roles in biotic and abiotic stress response in plants. However, the involvements of FA in chilling stress tolerance and the molecular mechanisms related to mitogen-activated protein kinase (MAPK) in tomato fruit are still elusive. In this study, the effect of exogenous FA on chilling resistance of tomato fruit was investigated. In addition, CRISPR/Cas9-mediated slmapk3 mutants were used to investigate the relationship between FA and SlMAPK3 under chilling stress. The results showed that low temperature (4 ℃) induced increase of FA content and FA synthesis related genes (SlPAL5, SlC3H and SlCOMT) expression. In addition, exogenous FA reduced the severity of cold injury, up-regulated the expressions of SlMAPK3, SlCBF1 and SlICE1, and promoted the accumulation of proline and soluble protein content. However, knockout of SlMAPK3 reduced the chilling tolerance of tomato fruit and inhibited the activities of antioxidant enzymes (APX, POD, SOD and CAT) but induced the accumulation of H2O2. In the condition of low temperature (4 ℃), there was a high correlation between SlMAPK3 and FA synthesis related genes (SlPAL5, SlC3H, SlC4H and SlCOMT) in control fruit. However, knockout of SlMAPK3 inhibited the content of FA and the expression of those genes compared with the control, which suggested a close relationship between SlMAPK3 and FA. Specifically, the effects of FA on osmotic regulatory substance and antioxidant enzyme system as well as the gene expression of CBF (C-repeat binding transcription factor) pathway were reduced after knockout of SlMAPK3. These results unveil a function of FA in tomato fruit positively resistance to chilling stress by up-regulating the gene expression of CBF transcriptional pathway in MAPK3-dependent manner.

Mechanisms of Nitric Oxide in the Regulation of Chilling Stress Tolerance in Camellia sinensis

Tea [Camellia sinensis (L.)] plants are important economic crop in China. Chilling stress and freezing damages have seriously affected the quality of tea products that have been already regarded as the main restricting factors to industry’s development. Nitric oxide (NO) plays a crucial role in resistance of abiotic stresses. An experiment was conducted in an artificial climate chamber to study the effect of NO on tea plants grown under chilling stress (−2 °C) for 0, 6, 24, 48, and 72 h. Foliar application of sodium nitroprusside (SNP) at a rate of 500 μmol·L−1 was used as NO donor. The experiment contained two factors: the first was the foliar application with SNP or distilled water, and the scond one was the chilling (−2 °C) exposure time (0, 6, 24, 48, and 72 h). The effects of NO on membrane lipid peroxidation, osmotic adjustment substances, and antioxidant activity under cold stress were studied. In addition, the gene expression of CsICE1 and CsCBF1 in respond to NO addition were also investigated using real-time polymerase chain reaction (RT-PCR). The results show that foliar addition of NO (500 μmol·L−1 of SNP) reduce the relative conductivity of tea leaves, inhibits the elevated malondialdehyde content, promotes the accumulation of proline, soluble protein and sugar, and increases the superoxide dismutase, catalase activities, thereby alleviates the damage of cold stress on tea leaves. The CsICE1 expression in 500 μM SNP treatment was peaked at 24 h of low temperature stress, while it did not express at normal temperature. Therefore, the current study is considered a good scientific material in understanding how tea plants sense and defense the chilling stress and that plays an important role to improve the level of production and economic benefits. It is also provided significant theory bas to control chilling stress in tea plants.

Melatonin effects in enhancing chilling stress tolerance of pepper

Chilling stress is a type of low temperature stress that occurs when plants are exposed to temperatures below optimum but above 0 °C. It determines the geographical distribution of crop species that are of tropic and sub-tropic origin and causes huge losses every year. Thus, besides developing stress tolerant crop varieties, the use of various substances has become an important way of alleviating the adverse effects of abiotic stress conditions and melatonin has gained huge attention lately due to its proven anti-oxidative nature. The objective of the present study was to explore if exogenous application of melatonin through soil drench would mitigate the damage caused by chilling stress in pepper at seedling and flowering stages. Pepper seedlings and flowering plants were treated with melatonin after which they were subjected to chilling stress at 5 °C/10 °C (night/day) for 3 days. The results indicated that melatonin application resulted in reduced visual damage but increased leaf area and shoot mass in pepper seedlings. Melatonin treatment also improwed water relations, photosynthetic parameters and the activities of antioxidant enzymes while lowering malondialdehyde (MDA) and H2O2 contents and membrane permeability. When applied at flowering stage, melatonin doubled the early yield but caused slight increase in the final yield. Thus, the results of this research indicate that treatment of pepper plants with 5 µM melatonin through soil drench could be used to improve plant growth and early yield potential under chilling stress conditions.

Tomato calmodulin-like protein SlCML37 is a calcium (Ca2+) sensor that interacts with proteasome maturation factor SlUMP1 and plays a role in tomato fruit chilling stress tolerance

Calmodulin-like proteins (CMLs), as well as their targets, play significant roles in various key developmental and stress responses in the plant. In tomato (Solanum lycopersicum), there are at least 52 CML genes in its genome. However, most of their functions are not well known, especially in response to cold stress. Here, we investigated SlCML37 biochemical and structural characteristics, including a typical α-helical secondary structure and exposing its hydrophobic regions after binding to Ca2+. Then we certificated that SlCML37 protein could physically interact with SlUMP1 by using yeast two-hybrid, bimolecular florescence complementation (BiFC) and GST pull-down assays. Further analysis showed that SlCML37-transgenic tomato fruit conferred significantly improved tolerance to chilling stress. This study indicates a possible role of calmodulin-like protein-mediated proteasome assemble in the regulation of plant cold response.

Mitochondrial small heat shock protein and chilling tolerance in tomato fruit

Our previous report indicated that tomato (Solanum lycopersicum) fruit of two contrasting varieties in the chilling tolerance showed the opposite expression pattern of a mitochondrial small heat shock protein (M-sHSP23.8) gene after chilling stress. Thus, the fruit of the relatively tolerant variety Micro-Tom strongly accumulated M-sHSP23.8 transcripts while the susceptible var. Minitomato fruit did not. To test whether M-sHSP23.8 is involved in tomato fruit protection mechanisms against chilling stress, Minitomato fruit overexpressing M-sHSP23.8 (OE23.8) and knockdown Micro-Tom fruit with reduced levels of M-sHSP23.8 (amiR23.8) were developed. After chilling treatment, most of the amiR23.8 fruit failed to ripen normally, showed wilting and skin wrinkles, partial discoloration, and did not reach full red color. On the contrary, these chilling injury symptoms were significantly diminished in OE23.8 fruit, showing less visible deterioration after chilling. Fruit of OE23.8 and amiR23.8 showed opposite patterns of water loss, electrolyte leakage, and expression of the tomato catalase 1 gene compared to control fruit. Membrane lipidome profile evidenced that amiR23.8 fruit showed differential adjustment of extraplastidic and plastidic lipids and variations in the lipid remodeling compared to control fruit, suggesting alterations in the membrane integrity. The high sensitivity of Micro-Tom amiR23.8 fruit and the better performance of Minitomato OE23.8 fruit to chilling treatment indicate that sHSP23.8 may be crucial in the chilling stress tolerance in tomato fruit.

A tomato dynein light chain gene SlLC6D is a negative regulator of chilling stress

Dynein light chain (DLC) proteins are an important component of dynein complexes, which are widely distributed in plants and animals and involved in a variety of cellular processes. The functions of DLC genes in plant chilling stress remain unclear. In this study, we isolated a DLC gene from tomato, designated SlLC6D. Promoter analysis revealed many cis-elements involved in abiotic stress in the SlLC6D promoter. Expression of SlLC6D was induced by heat and salt stress, and inhibited by polyethylene glycol and chilling stress. Knockdown of SlLC6D in tomato exhibited low relative electrolyte leakage, malondialdehyde content, and reactive oxygen species (ROS) accumulation under chilling stress. The content of proline and activities of superoxide dismutase and peroxidase in knockdown lines were higher than in the wild type and overexpression lines during chilling stress. The high transcript abundances of three cold-responsive genes were detected in knockdown lines in response to chilling stress. Seedling growth of knockdown lines was significantly higher than that of the wild type and overexpression lines under chilling stress. These results suggest that SlLC6D is a negative regulator of chilling stress tolerance, possibly by regulating ROS contents and the ICE1–CBF–COR pathway.

Multiple Cold Tolerance Trait Phenotyping Reveals Shared Quantitative Trait Loci in Oryza sativa

BackgroundDeveloping chilling tolerant accessions of domesticated Asian rice is a potential source of significant crop improvement. The uniquely chilling sensitive nature of the tropically originating Oryza sativa make it the most important cereal crop that can gain significantly from improved tolerance to low temperatures. However, mechanisms underlying this complex trait are not fully understood. Oryza sativa has two subspecies with different levels of chilling tolerance, JAPONICA and INDICA, providing an ideal tool to investigate mechanistic differences in the chilling stress tolerance responses within this important crop species.ResultsThe Rice Diversity Panel 1 (RDP1) was used to investigate a core set of Oryza sativa accessions. The tools available for this panel allowed for a comprehensive analysis of two chilling tolerance traits at multiple temperatures across a 354-cultivar subset of the RDP1. Chilling tolerance trait values were distributed as mostly subpopulation specific clusters of Tolerant, Intermediate, and Sensitive accessions. Genome-wide association study (GWAS) mapping approaches using all 354 accessions yielded a total of 245 quantitative trait loci (QTL), containing 178 unique QTL covering 25% of the rice genome, while 40 QTL were identified by multiple traits. QTL mappings using subsets of rice accession clusters yielded another 255 QTL, for a total of 500 QTL. The genes within these multiple trait QTL were analyzed for Gene Ontology (GO) term and potential pathway enrichments. Terms related to “carbohydrate biosynthesis”, “carbohydrate transmembrane transport”, “small molecule protein modification”, and “plasma membrane” were enriched from this list. Filtering was done to identify more likely candidate pathways involved in conferring chilling tolerance, resulting in enrichment of terms related to “Golgi apparatus”, “stress response”, “transmembrane transport”, and “signal transduction”.ConclusionsTaken together, these GO term clusters revealed a likely involvement of Golgi-mediated subcellular and extracellular vesicle and intracellular carbohydrate transport as a general cold stress tolerance response mechanism to achieve cell and metabolic homeostasis under chilling stress.

Chilling stress tolerance of two soya bean cultivars: Phenotypic and molecular responses

AbstractChilling stress is a major factor limiting the yield of soya bean [Glycine max (L.) Merr.] on a global scale. However, the regulatory network that controls the chilling response of soya bean remains unclear. In the present study, phenotyping and quantitative analyses of miRNAs in soya bean under chilling stress were carried out to determine the impact of environmental constraints on soya bean productivity. Measurements done during soya bean growth in chilling along with the results of field trials indicated that the cultivars Augusta and Fiskeby V responded differently to low temperatures. Although chilling affected the reproductive development of both cultivars, the final seed output remained unchanged. The differential expression of miR169, miR319, miR397 and miR398 under cold stress was detected using ddPCR. Upon chilling in the reproductive stage, we found that these miRNAs had contrasting expression profiles in Augusta and Fiskeby V. A set of candidate target genes was predicted based on degradome sequencing data. A negative correlation was found between the expression of miR169, miR319 and miR398 and their targets in the roots of both cultivars. Our work elucidates the impact of chilling stress on the productivity of two soya bean cultivars and reveals the importance of miRNA involvement in the low temperature response.

Türk Mısır (Zea mays L.) Hibridlerinin Üşüme Stresine Karşı Toleranslarında Genetik Varyasyonlar

Maize (Zea mays L.) is a tropical crop and chilling temperatures (below 15 ºC) cause growth retardation and yield losses. The development of chilling-tolerant maize varieties is a main goal of plant breeders in order to produce maize under cool climates. Hybrids are more vigorous then their parents, including being more tolerant to diverse stresses. However, stress screening is an obstacle. This study aims to evaluate chilling stress tolerance of Turkish maize hybrids and determine suitable indicators for selection of the most tolerant hybrid. Nine hybrids were subjected to low night temperature following germination until the third leaf was fully enlarged. Hybrids were evaluated at morphological, cellular and physiological levels by comparison with control seedlings. The data were analyzed by kinematic analysis and statistical tools. The findings showed that all indicators significantly differed among the hybrids. Indicators such as leaf elongation rate (LER), mature cell length (MCL) and cell production (CP) increase our understanding of stress tolerance by making connections between phenotype and cellular functions. Fresh and dry weight of shoot (SFW and SDW) were observed to be useful indicators to uncover relatedness between growth and the physiological stress response of seedlings. In conclusion, this study defines beneficial indicators for breeding studies at early seedling screening of maize hybrids which are displayed genetic variation for chilling stress tolerance.

Elucidating the regulatory roles of microRNAs in maize (Zea mays L.) leaf growth response to chilling stress.

MAIN CONCLUSION: miRNAs control leaf size of maize crop during chilling stress tolerance by regulating developmentally important transcriptional factors and sustaining redox homeostasis of cells. Chilling temperature (0-15°C) is a major constraint for the cultivation of maize (Zea mays) which inhibits the early growth of maize leading to reduction in leaf size. Growth and development take place in meristem, elongation, and mature zones that are linearly located along the leaf base to tip. To prevent shortening of leaf caused by chilling, this study aims to elucidate the regulatory roles of microRNA (miRNA) genes in the controlling process switching between growth and developmental stages. In this respect, hybrid maize ADA313 seedlings were treated to the chilling temperature which caused 26% and 29% reduction in the final leaf length and a decline in cell production of the fourth leaf. The flow cytometry data integrated with the expression analysis of cell cycle genes indicated that the reason for the decline was a failure proceeding from G2/M rather than G1/S. Through an miRNome analysis of 321 known maize miRNAs, 24, 6, and 20 miRNAs were assigned to putative meristem, elongation, and mature zones, respectively according to their chilling response. To gain deeper insight into decreased cell production, in silico, target prediction analysis was performed for meristem specific miRNAs. Among the miRNAs, miR160, miR319, miR395, miR396, miR408, miR528, and miR1432 were selected for confirming the potential of negative regulation with their predicted targets by qRT-PCR. These findings indicated evidence for improvement of growth and yield under chilling stress of the maize.

Mitigating chilling stress of pepper plant (Capsicum annuum L.) using Dimethyl Ether combustion gas in controlled greenhouse

In this study, the possibility of enhancing chilling stress tolerance of pepper plant (Capsicum annuum Linnaeus) during early growth stages was investigated using DME combustion gas in controlled greenhouse. The experiment was conducted to determine the performance of DME combustion gas when used as a fuel for DME burner for raising temperature and CO2 concentration in greenhouse and also to examine its effects on morphology parameters of hot pepper in winter season. To analyze the relationship between the application of DME and morphology parameters of pepper plant, three treatments (DME-1, DME-2 and DME-3) for three controlled greenhouses were assayed. DME-1 and DME-2 treatments consisted of average DME flow quantity in duct were 17.4 m3/min and 10.2 m3/min, respectively to greenhouse-1 and greenhouse-2 and no DME gas was supplied to greenhouse-3 which was left as control (DME-3). Morphology parameters such as plant height, leaf area and leaf area index (LAI), net assimilation rate (NAR), relative growth rate (RGR), fresh weight and dry weight were measured for eight weeks for each treatment and analyzed using completely randomized designs through analysis of variance with a significance level of P < 0.05. Although DME-1, DME-2 and DME-3 received same crop management practices and controlled environmental factors, the highest changes (p < 0.05) of plant height, leaf area, LAI and fresh weight were found from the DME-1 treatment, followed by DME-2. A comparison of relative growth rates among the treatments indicated more rapid relative growth rate of morphology parameters at vegetative phase of plant implying better yield. Therefore endorsed quantify of DME combustion gas for a specified crop can be applied to greenhouse to improve the plant growth and enhance yield with mitigating chilling stress in winter season.

Physiological response and transcription profiling analysis reveal the role of glutathione in H2S-induced chilling stress tolerance of cucumber seedlings

Recent reports have uncovered the multifunctional role of H2S in the physiological response of plants to biotic and abiotic stresses. Here, we studied whether NaHS (an H2S donor) pretreatment could provoke the tolerance of cucumber (Cucumis sativus L.) seedlings subsequently exposed to chilling stress and whether glutathione was involved in this process. Results showed that cucumber seedlings sprayed with NaHS exhibited remarkably increased chilling tolerance, as evidenced by the observed plant tolerant phenotype, as well as the lower levels of electrolyte leakage (EL), malondialdehyde (MDA) content, hydrogen peroxide (H2O2) content and RBOH mRNA abundance, compared with the control plants. In addition, NaHS treatment increased the endogenous content of the reduced glutathione (GSH) and the ratio of reduced/oxidized glutathione (GSH/GSSG), meanwhile, the higher net photosynthetic rate (Anet), the light-saturated CO2 assimilation rate (Asat), the photochemical efficiency (Fv/Fm) and the maximum photochemical efficiency of PSII in darkness (ФPSII) as well as the mRNA levels and activities of the key photosynthetic enzymes (Rubisco, TK, SBPase and FBA) were observed in NaHS-treated seedlings under chilling stress, whereas this effect of NaHS was weakened by buthionine sulfoximine (BSO, an inhibitor of glutathione) or 6-Aminonicotinamide (6-AN, a specific pentose inhibitor and thus inhibits the NADPH production), which preliminarily proved the interaction between H2S and GSH. Moreover, transcription profiling analysis revealed that the GSH-associated genes (GST Tau, MAAI, APX, GR, GS and MDHAR) were significantly up-regulated in NaHS-treated cucumber seedlings, compared to the H2O-treated seedlings under chilling stress. Thus, novel results highlight the importance of glutathione as a downstream signal of H2S-induced plant tolerance to chilling stress.

ZmDREB1A Regulates RAFFINOSE SYNTHASE Controlling Raffinose Accumulation and Plant Chilling Stress Tolerance in Maize.

Raffinose accumulation is positively correlated with plant chilling stress tolerance; however, the understanding of the function and regulation of raffinose metabolism under chilling stress remains in its infancy. RAFFINOSE SYNTHASE (RAFS) is the key enzyme for raffinose biosynthesis. In this study, we report that two independent maize (Zea mays) zmrafs mutant lines, in which raffinose was completely abolished, were more sensitive to chilling stress and their net photosynthetic product (total soluble sugars and starch) accumulation was significantly decreased compared with controls after chilling stress. A similar characterization of the maize dehydration responsive element (DRE)-binding protein 1A mutant (zmdreb1a) showed that ZmRAFS expression and raffinose content were significantly decreased compared with its control under chilling stress. Overexpression of maize ZmDREB1A in maize leaf protoplasts increased ZmDREB1A amounts, which consequently upregulated the expression of maize ZmRAFS and the Renilla LUCIFERASE (Rluc), which was controlled by the ZmRAFS promoter. Deletion of the single dehydration-responsive element (DRE) in the ZmRAFS promoter abolished ZmDREB1A's influence on Rluc expression, while addition of three copies of the DRE in the ZmRAFS promoter dramatically increased Rluc expression when ZmDREB1A was simultaneously overexpressed. Electrophoretic mobility shift assays and chromatin immunoprecipitation-quantitative PCR demonstrated that ZmDREB1A directly binds to the DRE motif in the promoter of ZmRAFS both in vitro and in vivo. These data demonstrate that ZmRAFS, which was directly regulated by ZmDREB1A, enhances both raffinose biosynthesis and plant chilling stress tolerance.

Genes, pathways and transcription factors involved in seedling stage chilling stress tolerance in indica rice through RNA-Seq analysis

BackgroundRice plants show yellowing, stunting, withering, reduced tillering and utimately low productivity in susceptible varieties under low temperature stress. Comparative transcriptome analysis was performed to identify novel transcripts, gain new insights into different gene expression and pathways involved in cold tolerance in rice.ResultsComparative transcriptome analyses of 5 treatments based on chilling stress exposure revealed more down regulated genes in susceptible and higher up regulated genes in tolerant genotypes. A total of 13930 and 10599 differentially expressed genes (DEGs) were detected in cold susceptible variety (CSV) and cold tolerant variety (CTV), respectively. A continuous increase in DEGs at 6, 12, 24 and 48 h exposure of cold stress was detected in both the genotypes. Gene ontology (GO) analysis revealed 18 CSV and 28 CTV term significantly involved in molecular function, cellular component and biological process. GO classification showed a significant role of transcription regulation, oxygen, lipid binding, catalytic and hydrolase activity for tolerance response. Absence of photosynthesis related genes, storage products like starch and synthesis of other classes of molecules like fatty acids and terpenes during the stress were noticed in susceptible genotype. However, biological regulations, generation of precursor metabolites, signal transduction, photosynthesis, regulation of cellular process, energy and carbohydrate metabolism were seen in tolerant genotype during the stress. KEGG pathway annotation revealed more number of genes regulating different pathways resulting in more tolerant. During early response phase, 24 and 11 DEGs were enriched in CTV and CSV, respectively in energy metabolism pathways. Among the 1583 DEG transcription factors (TF) genes, 69 WRKY, 46 bZIP, 41 NAC, 40 ERF, 31/14 MYB/MYB-related, 22 bHLH, 17 Nin-like 7 HSF and 4C3H were involved during early response phase. Late response phase showed 30 bHLH, 65 NAC, 30 ERF, 26/20 MYB/MYB-related, 11 C3H, 12 HSF, 86 Nin-like, 41 AP2/ERF, 55 bZIP and 98 WRKY members TF genes. The recovery phase included 18 bHLH, 50 NAC, 31 ERF, 24/13 MYB/MYB-related, 4 C3H, 4 HSF, 14 Nin-like, 31 bZIP and 114 WRKY TF genes.ConclusionsTranscriptome analysis of contrasting genotypes for cold tolerance detected the genes, pathways and transcription factors involved in the stress tolerance.

Cold stress tolerance of soybeans during flowering: QTL mapping and efficient selection strategies under controlled conditions

AbstractBreeding soybeans for higher latitudes requires cultivars with an increased chilling stress tolerance, especially when flowering occurs. Phenotyping in climate chambers to select for this trait is labour‐intensive and requires an optimal allocation of resources due to limited space. We screened a diversity panel of 35 early maturity cultivars and a biparental population of 103 RILs for their cold stress tolerance at flowering stage. Pod number under control and stress conditions is highly heritable and showed only a weak correlation between the two treatments. Based on different testing scenarios, we could show that testing more genotypes with less replicates yields much higher responses to selection and hence should be pursued in such climate‐controlled experiments. We identified quantitative trait loci (QTL) for pod number under both conditions (chromosomes 7 and 13) and a cold tolerance‐specific QTL (chromosome 11). Furthermore, we performed genomic predictions using different test set scenarios and prediction models, showing that genomic prediction is a promising tool to select for cold stress tolerance, particularly if known QTL can be used as fixed effects in the model.

Overexpression of Solanum habrochaites microRNA319d (sha-miR319d) confers chilling and heat stress tolerance in tomato (S. lycopersicum)

BackgroundMicroRNA319 (miR319) acts as an essential regulator of gene expression during plant development and under stress conditions. Although the role of miR319a in regulating leaf development has been well studied in tomato (Solanum lycopersicum), the function of the recently discovered wild tomato Solanum habrochaites miRNA319d (sha-miR319d) remains poorly understood. In this study, we overexpressed sha-miR319d in cultivated tomato ‘Micro-Tom’ to further investigate its role in tomato temperature stress responses.ResultsUnder chilling or heat stress, sha-miR319d-overexpressing plants showed enhanced stress tolerance, including lower relative electrolyte leakage (REL), malondialdehyde (MDA) concentration, O2− generation and H2O2 concentration and higher chlorophyll contents and Fv/Fm values than wild-type (WT) plants. Overexpression of sha-miR319d enhanced the activities of superoxide dismutase (SOD) and catalase (CAT), with possible correlation with elevated expression levels of the genes FeSOD, CuZnSOD and CAT. Moreover, different expression levels of key genes involved in chilling (MYB83 and CBF1), heat (HsfA1a, HsfA1b and Hsp90), and reactive oxygen species (ROS) (ZAT12 and ZAT10) signaling in transgenic plants and WT were determined, suggesting a role for sha-miR319d in regulating tomato temperature stress via chilling, heat and ROS signaling. Silencing GAMYB-like1 increased tomato chilling tolerance as well as the expression levels of CBF1, CuZnSOD, CAT, APX1, APX2, ZAT12 and ZAT10. Additionally, overexpression of sha-miR319d in tomato caused plant leaf crinkling and reduced height.ConclusionsOverexpression of sha-miR319d confers chilling and heat stress tolerance in tomato. Sha-miR319d regulates tomato chilling tolerance, possibly by inhibiting expression of GAMYB-like1 and further alters chilling, heat and ROS signal transduction. Our research provides insight for further study of the role of sha-miR319d in tomato growth and stress regulation and lays a foundation for the genetic improvement of tomato.

Uniconazole confers chilling stress tolerance in soybean (Glycine max L.) by modulating photosynthesis, photoinhibition, and activating oxygen metabolism system

The current study investigates a possible mediatory role of uniconazole in improving chilling stress tolerance in chilling-sensitive (Hefeng 50) and chilling-tolerant (Kenfeng 16) soybean varieties. Chilling stress decreased photosynthetic pigments and inhibited net photosynthetic rate which was ascribed to stomatal limitation. The maximum quantum efficiency of PSII primary photochemistry and electron transport rate were lower in uniconazole-treated plants compared with the control. The increased contents of superoxide (O2*-) and malondialdehyde during chilling stress indicated oxidative stress. Chilling stress reduced glutathione and ascorbic acid contents, and promoted peroxidase, glutathione reductase, and ascorbate peroxidase activities. Uniconazole improved the tolerance of chilled plants. This might be due to better antioxidant defense mechanisms including higher contents of antioxidants and activities of antioxidant enzymes, which retard lipid peroxidation. Thus, uniconazole has a positive effect and improves the chilling resistance of soybean.

The tomato 2-oxoglutarate-dependent dioxygenase gene SlF3HL is critical for chilling stress tolerance

Low temperature is a major stress that severely affects plant development, growth, distribution, and productivity. Here, we examined the function of a 2-oxoglutarate-dependent dioxygenase-encoding gene, SlF3HL, in chilling stress responses in tomato (Solanum lycopersicum cv. Alisa Craig [AC]). Knockdown (KD) of SlF3HL (through RNA interference) in tomato led to increased sensitivity to chilling stress as indicated by elevated levels of electrolyte leakage, malondialdehyde (MDA) and reactive oxygen species (ROS). In addition, the KD plants had decreased levels of proline and decreased activities of peroxisome and superoxide dismutase. The expression of four cold-responsive genes was substantially reduced in the KD plants. Furthermore, seedling growth was significantly greater in AC or SlF3HL-overexpression plants than in the KD plants under either normal growth conditions with methyl jasmonate (MeJA) or chilling stress conditions. SlF3HL appears to positively regulate JA accumulation and the expression of JA biosynthetic and signaling genes under chilling stress. Together, these results suggest that SlF3HL is a positive regulator of chilling stress tolerance and functions in the chilling stress tolerance pathways, possibly by regulating JA biosynthesis, JA signaling, and ROS levels.

Phenological Changes in the Chlorophyll Content and Its Fluorescence in Field-Grown Sugarcane Clones Under Over-Wintering Conditions

As a step toward breeding cultivars with tolerance to chilling stress, phenological changes in chlorophyll content (SPAD index) and its fluorescence (Fv/Fm) were investigated under over-wintering conditions using different sugarcane clones. A leading commercial cultivar in Japan, NiF8, and two interspecific lines, KY11-6114 and KY08-1200, were tested in this study. Daily minimum temperature decreased gradually with the advance of winter, and the lowest temperature of 1.2 °C was recorded in January. Although the temperature increased toward spring season, it remained below 10 °C until the end of experiment. Stem elongations in KY11-6114 and KY08-1200 during winter were significantly greater than in NiF8. The decrease in SPAD index was calculated from the difference between the beginning of winter and each measuring time. KY08-1200 and KY11-6114, with longer stem elongation, had a smaller decrease in SPAD index than NiF8 under over-wintering conditions. The Fv/Fm of all three clones decreased in January when the lowest temperature was recorded and recovered toward spring. Among three clones, KY08-1200 was less affected by chilling stress and presented a higher value of Fv/Fm up to the end of experiment. Considering these results, we concluded that the decreased chlorophyll content measured by the SPAD index was a simple indicator for screening chilling-tolerant clones.