Tolerance To Low Temperature Stress Research Articles

Astaxanthin supplementation enhances low-temperature stress tolerance, immune-related genes, and resistance to Vibrio parahaemolyticus in Whiteleg Shrimp Penaeus vannamei

Astaxanthin supplementation enhances low-temperature stress tolerance, immune-related genes, and resistance to Vibrio parahaemolyticus in Whiteleg Shrimp Penaeus vannamei

Mapping the genetic architecture of low-temperature stress tolerance in citron watermelon.

Sweet-fleshed watermelon (Citrullus lanatus) is an important vegetable crop of the tropical origin. It is widely grown and consumed around the world for its hydration and nutritional quality values. Low-temperature stress can affect early planting, seedling establishment, and expansion of crop production to new areas. A collection of 122 citron watermelon (Citrullus amarus) accessions were obtained from the USDA's National Plant Germplasm Repository System gene bank in Griffin, GA. The accessions were genotyped using whole genome resequencing to generate single nucleotide polymorphisms (SNPs) molecular markers and screened under cold-stressed and non-stressed control conditions. Four low-temperature stress tolerance related traits including shoot biomass, vine length, maximum quantum efficiency of photosystem II, and chlorophyll content were measured under cold-stressed and non-stressed control treatment conditions. Correlation analysis revealed the presence of positive relationships among traits. Broad-sense heritability for all traits ranged from 0.35 to 0.73, implying the presence of genetic contributions to the observed phenotypic variation. Genomic regions underlying these traits across several citron watermelon chromosomes were identified. Four low-temperature stress tolerance related putative candidate genes co-located with the peak SNPs from genome-wide association study. These genomic regions and marker information could potentially be used in molecular breeding to accelerate genetic improvements for low-temperature stress tolerance in watermelon.

Genome-wide identification of XTH gene family in Musa acuminata and response analyses of MaXTHs and xyloglucan to low temperature.

Banana (Musa spp.) production is seriously threatened by low temperature (LT) in tropical and subtropical regions. Xyloglucan endotransglycosylase/hydrolases (XTHs) are considered chief enzymes in cell wall remodelling and play a central role in stress responses. However, whether MaXTHs are involved in the low temperature stress tolerance in banana is not clear. Here, the identification and characterization of MaXTHs were carried out, followed by prediction of their cis-acting elements and protein-protein interactions. In addition, candidate MaXTHs involved in banana tolerance to LT were screened through a comparison of their responses to LT between tolerant and sensitive cultivars using RNA-Seq analysis. Moreover, immunofluorescence (IF) labelling was employed to compare changes in the temporal and spatial distribution of different types of xyloglucan components between these two cultivars upon stress. In total, 53 MaXTHs have been identified, and all were predicted to be located in the cell wall, 14 of them also in the cytoplasm. Only 11 MaXTHs have been found to interact with other proteins. Among 16 MaXTHs with LT responsiveness elements, MaXTH26/29/32/35/50 (Group I/II members) and MaXTH7/8 (Group IIIB members) might be involved in banana tolerance to LT stress. IF results suggested that the content of xyloglucan components recognized by CCRC-M87/103/104/106 antibodies might be negatively related to banana chilling tolerance. In conclusion, we have identified the MaXTH gene family and assessed cell wall re-modelling under LT stress. These results will be beneficial for banana breeding against stresses and enrich the cell wall-mediated resistance mechanism in plants to stresses.

Transcriptional regulatory cascade of LcMYB71 and LcNAC73 affects low-temperature and drought stress response in Lonicera caerulea

The development of stress tolerance is regulated via the transcriptional regulatory networks involving regulatory homeostasis mediated by protein–DNA interactions. LcNAC73 from Lonicera caerulea was characterized to understand the underlying mechanism of low-temperature and drought stress response in L. caerulea. To better understand the transcription pathway of LcNAC73, we cloned the promoter and screened proteins that could interact with the promoter. Using Yeast one-hybrid, electrophoretic mobility shift, and chromatin immunoprecipitation assays, we found that the LcMYB71 protein specifically bound to the promoter of LcNAC73. The transient transformation and stable transgenic system were used to produce transgenic L. caerulea plants with overexpressed and silenced LcNAC73, elucidating the effect of LcNAC73 on low-temperature and drought stress tolerance. LcNAC73 positively regulated the proline content and enhanced the scavenging of reactive oxygen species, thus improving tolerance to low-temperature and drought stress. Further studies revealed that LcMYB71 and LcNAC73 had similar functions and could improve plant low-temperature and drought tolerance. It is necessary to identify the upstream regulators of a specific gene to characterize gene functions and the associated transcriptional pathways.

Metabolomics-based exploration the response mechanisms of Saussurea involucrata leaves under different levels of low temperature stress

BackgroundSaussurea involucrata (Sik.) is alpine plant that have developed special adaptive mechanisms to resist adverse environmental conditions such as low temperature chilling during long-term adaptation and evolution. Exploring the changes of its metabolites under different temperature stresses is helpful to gain insight into its cold stress tolerance.MethodsUltra-performance liquid chromatography and tandem mass spectrometry were used to analyze the metabolites in the leaves of Sik. under low different temperature stress conditions. Results: A total of 753 metabolites were identified, and 360 different metabolites were identified according to the Kyoto Encyclopedia of Genes and Genomes (KEGG) involved in the biosynthesis of secondary metabolites and amino acids and sugars. Sucrose and trehalose synthesis, glycolysis, tricarboxylic acid cycle, pentose phosphate pathway, glutamic acid-mediated proline biosynthesis, purine metabolism, amino acid metabolism, phenylpropane synthesis pathway metabolites all respond to low temperature stress. Under cold stress conditions, carbohydrates in Sik. leaves accumulate first than under freezing conditions, and the lower the temperature under freezing conditions, the less amino acids accumulate, while the phenolic substances increase. The expression of various substances in LPE and LPC increased more than 10-fold after low temperature stress compared with the control, but the content of LPE and LPC substances decreased after cold adaptation. In addition, purines and phenolics decreased and amino acids accumulated significantly under freezing conditions. Conclusion: The metabolic network of Sik. leaves under different low temperature stress conditions was proposed, which provided a reference for further exploration of the metabolic mechanism related to low temperature stress tolerance of Sik.

Lysine malonylation of DgnsLIPID TRANSFER PROTEIN1 at the K81 site improves cold resistance in chrysanthemum.

Lysine malonylation (Kmal) is a recently discovered posttranslational modification, and its role in the response to abiotic stress has not been reported in plants. In this study, we isolated a nonspecific lipid transfer protein, DgnsLTP1, from chrysanthemum (Dendranthema grandiflorum var. Jinba). Overexpression and CRISPR-Cas9-mediated gene editing of DgnsLTP1 demonstrated that the protein endows chrysanthemum with cold tolerance. Yeast 2-hybrid, bimolecular fluorescence complementation, luciferase complementation imaging, and coimmunoprecipitation experimental results showed that DgnsLTP1 interacts with a plasma membrane intrinsic protein (PIP) DgPIP. Overexpressing DgPIP boosted the expression of DgGPX (glutathione peroxidase), increased the activity of GPX, and decreased the accumulation of reactive oxygen species (ROS), thereby enhancing the low-temperature stress tolerance of chrysanthemum, while the CRISPR-Cas9-mediated mutant dgpip inhibited this process. Transgenic analyses in chrysanthemum showed that DgnsLTP1 improves the cold resistance of chrysanthemum in a DgPIP-dependent manner. Moreover, Kmal of DgnsLTP1 at the K81 site prevented the degradation of DgPIP in Nicotiana benthamiana and chrysanthemum, further promoted DgGPX expression, enhanced GPX activity, and scavenged excess ROS produced by cold stress, thereby further enhancing the cold resistance of chrysanthemum.

Effect of Seed Dressing with Gibberellins and Brassinosteroids on Enzymatic Activity and Seed Quality of Soya Bean at Different Vigour Levels Under Low Temperature

Gibberellin (GA3 ) and brassinosteroid (EBL) interactions can stimulate germination, extend seedling growth and induce low temperature stress tolerance. The effects of GA3 and EBL on seed quality, α-amylase and total dehydro genase activities of soya bean seeds at different vigour and temperature levels were studied. The results showed that medium vigour seeds dressed with 100 ppm GA3, 0.25 ppm EBL plus 50 ppm GA3, and 0.50 ppm EBL plus 100 ppm GA3 had significantly higher germination (GP) and seedling vigour rates (SVR) than those of untreated seeds. Similarly, 0.50 ppm EBL resulted in higher SVR of low and medium vigour seeds when compared to the control under low temperature. All soya bean seeds dressed with 100 ppm GA3 had higher GP, vigour, shoot and root lengths, and SVR under both temperatures than those of the untreated seeds, and mean germination time decreased. At 15°C, all seeds dressed with 0.50 ppm EBL plus 100 ppm GA3 had higher α-amylase activity than the untreated seeds, whereas seeds with low and medium seed vigour dressed with 100 ppm GA3 and 0.25 ppm EBL plus 50 ppm GA3 had higher total dehydrogenase activity than the untreated seeds.

Thermal stress-induced physiological and biochemical alterations in papaya genotypes

Low-temperature stress significantly affects physiological processes inducing plant growth hindrance,and reducing crop productivity. The present study aimed to understand the low-temperature stress inducedphysio-chemical behaviour of five papaya genotypes (Pusa Nanha, Red Lady, P-9-5, P-7-9 and one wild relativespecies Vasconcellea cundinamarcensis). Low temperature stress significantly decreased the canopy gasexchange parameters, relative water content (RWC), membrane stability index (MSI) and chlorophyll contentin all the papaya genotypes, while tending to increase the total soluble sugars, proline and total solubleproteins, although the alterations were genotype-specific. V. cundinamarcensis showed greater tolerance tolow-temperature stress followed by P-9-5 and P-7-9 than other genotypes by maintaining the highest RWC,MSI, total soluble proteins, chlorophyll and proline contents. Our results showed that the chlorophyll content,membrane lipid peroxidation and MSI could be used as the indices for the screening of potential papayagenotypes against cold tolerance.

GhGTG1 enhances cold stress tolerance by improving sensitivity to ABA in cotton and Arabidopsis

Cold stress is a potent abiotic stress resulting in cotton yield and fiber quality loss. We hypothesized that GhGTG1 could increase low temperature stress tolerance by improving the sensitivity to ABA. Genome-wide identification, biochemical traits and functional characterization of GhGTG1, were investigated under different levels of ABA and cold stress. GhGTG1 had two highly conserved functional domains (ABA_GPCR, GPHR_N) in all cotton species. Under ABA treatment, over expression of GhGTG1 in Arabidopsis had a lower germination rate and root elongation. While under 4 ℃ stress, transgenic plants had a higher germination rate and root elongation. This indicate that GhGTG1 improved sensitivity to ABA under cold stress. In transgenic plants, CAT and SOD activity was increased, while H2O2 and MDA content decreased. Less trypan blue and DAB staining area suggested that GhGTG1 enhances cold stress resistance. Under 4 ℃ treatment, silence cotton seedlings through VIGS method, resulted in a poor growth, lower relative leaf water content, chlorophyll content but a higher ion leakage and excised leaf water loss. The activity of CAT and SOD decreased, H2O2 and MDA content was increased. Two marker genes (OST1 and ABCG40) are associated with the stomatal movement, but these genes were substantially suppressed. This suggesting that GhGTG1 can induce cold stress tolerance by improving ABA sensitivity Via., maintaining stomatal movement. These data will provide new insight of cold resistance mechanism in cotton and further will help the breeder to develop new cotton cold stress tolerance germplasm.

Effect of shading on physiological attributes and comparative transcriptome analysis of Camellia sinensis cultivar reveals tolerance mechanisms to low temperatures.

Tea is a vital beverage crop all over the world, including in China. Low temperatures restrict its growth, development, and terrestrial distribution, and cold event variability worsens cold damage. However, the physiological and molecular mechanisms of Camellia sinensis under shade in winter remain unclear. In our study, tea leaves were utilized for physiological attributes and transcriptome analysis in November and December in three shading groups and no-shade control plants. When compared to the no-shade control plants, the shading group protected tea leaves from cold damage, increased photochemical efficiency (Fv/Fm) and soil plant analysis development (SPAD), and sustained chlorophyll a, chlorophyll b, chlorophyll, and carotenoid contents by physiological mean. Then, transcriptome analysis revealed 20,807 differentially expressed genes (DEGs) and transcription factors (TFs) in November and December. A comparative study of transcriptome resulted in 3,523 DEGs and many TFs under SD0% vs. SD30%, SD0% vs. SD60%, and SD0% vs. SD75% of shading in November and December. Statistically, 114 DEGs were downregulated and 72 were upregulated under SD0% vs. SD30%. SD0% vs. SD60% resulted in 154 DEGs, with 60 downregulated and 94 upregulated. Similarly, there were 505 DEGs of which 244 were downregulated and 263 were upregulated under SD0% vs. SD75% of shading throughout November. However, 279 DEGs were downregulated and 105 were upregulated under SD0% vs. SD30%. SD0% vs. SD60% resulted in 296 DEGs, with 172 downregulated and 124 upregulated. Finally, 2,173 DEGs were regulated in December, with 1,428 downregulated and 745 upregulated under SD0% vs. SD75%. These indicate that the number of downregulated DEGs in December was higher than the number of upregulated DEGs in November during low temperatures. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses of differentially expressed genes were highly regulated in the photosynthesis, plant hormone signal transduction, and mitogen-activated protein kinase (MAPK) signaling pathways. However, qRT-PCR and RNA-seq relative expression of photosynthetic (DEGs) Lhcb2 in both November and December, plant hormone (DEGs) BRI1 and JAZ in November and IAA and ERF1 in December, and key DEGs of MAPK signal transduction FLS2, CHIB, and MPK4 in November and RBOH, MKK4_5, and MEKK1 in December in three shading groups and no-shade control plants responded to tea cold tolerance. The enhanced expression of light-harvesting photosystem I gene Lhca5, light-harvesting photosystem II gene Lhcb2, and mitogen-activated protein kinases MEKK1 and MPK4/6 enhance the cold-tolerance mechanism of C. sinensis. These comprehensive transcriptomic findings are significant for furthering our understanding of the genes and underlying regulatory mechanisms of shade-mediated low-temperature stress tolerance in horticultural crops.

Physiological and Transcriptomic Analyses Revealed That Humic Acids Improve Low-Temperature Stress Tolerance in Zucchini (Cucurbita pepo L.) Seedlings.

Zucchini (Cucurbita pepo L.) is one of the main vegetable crops grown under protected cultivation in northern China. Low-temperature (LT) stress severely inhibits the growth of zucchini seedlings, resulting in reductions in yield and quality. Here, using three kinds of different humic acids, including coal-based humic acid (CHA), fulvic acid (FA), and biochemical humic acid (BHA), we investigated the effects of humic acids against LT stress (5 °C) in zucchini seedlings. Treatment with all three kinds of humic acids improves LT stress tolerance by decreasing oxidative damage through increases in antioxidative enzyme activities and the contents of soluble sugar and proline in zucchini seedlings, especially after BHA application. Comparative transcriptomic analysis revealed that a total of 17 differentially expressed genes (DEGs) were commonly induced in the leaves of FA-, CHA-, and BHA-treated zucchini seedlings under LT stress, including calmodulin, ethylene-responsive transcription factors (TFs), peroxidases, and 10 TFs, including two NAC and seven WRKY genes. Altogether, these results indicated that supplementation with humic acids reprograms plant metabolism and modulates the expression of genes involved in ROS scavenging, phytohormone metabolism, or signaling pathways, finally improving LT stress tolerance in zucchini seedlings.

Genome-Wide Analyses of Thaumatin-like Protein Family Genes Reveal the Involvement in the Response to Low-Temperature Stress in Ammopiptanthus nanus.

Thaumatin-like proteins (TLPs), a family of proteins with high sequence similarity to thaumatin, are shown to be involved in plant defense, and are thus classified into the pathogenesis related protein family 5. Ammopiptanthus nanus is a rare evergreen broad-leaved shrub distributed in the temperate zone of Central Asia, which has a high tolerance to low-temperature stress. To characterize A. nanus TLPs and understand their roles in low-temperature response in A. nanus, a comprehensive analysis of the structure, evolution, and expression of TLP family proteins was performed. A total of 31 TLP genes were detected in the A. nanus genome, and they were divided into four groups based on their phylogenetic positions. The majority of the AnTLPs contained the conserved cysteine residues and were predicted to have the typical three-dimensional structure of plant TLPs. The primary modes of gene duplication of the AnTLP family genes were segmental duplication. The promoter regions of most AnTLP genes contain multiple cis-acting elements related to environmental stress response. Gene expression analysis based on transcriptome data and fluorescence quantitative PCR analysis revealed that several AnTLP genes were involved in cold-stress response. We further showed that a cold-induced AnTLP gene, AnTLP13, was localized in apoplast, and heterologous expression of the AnTLP13 in Escherichia coli and yeast cells and tobacco leaves enhanced low-temperature stress tolerance when compared with the control cells or seedlings. Our study provided important data for understanding the roles of TLPs in plant response to abiotic stress.

Root Architectures of Hybrid Pepper Variety Candidates with Low Temperature Stress Tolerance

Düşük sıcaklık stresine dayanıklılık yönünden bitki türleri arasında genotipik düzeyde farklılıklar bulunmaktadır. Son yıllarda düşük sıcaklığa tolerant yeni çeşitler geliştirilmektedir. Bu çalışmada, hibrit çeşit ıslahı ile düşük sıcaklığa tolerant olarak geliştirilen 28 F1 hibrit dolmalık biber çeşit adayının kök yapıları ve köklenme düzeylerinin karşılaştırılması amaçlanmıştır. Hibrit dolmalık biber çeşit adaylarının hem serada ve hem de açıkta birçok kök parametresi yönünden, kontrol çeşide (Benino F1) göre daha iyi bir köklenme yapısına sahip olduğu tespit edilmiştir. Ayrıca biber genotiplerinin kök mimarileri yönünden fenotipik çeşitliliğin oldukça yüksek olduğu belirlenmiştir. Çalışmada; ortalama toplam kök uzunluğu, 764.48 cm (HD-6) ile 1120.40 cm (HD-16), kök yüzey alanı 619.47 cm2 (HD-9) ile 963.14 cm2 (HD-26), kök çapı 2.50 (HD-3) ile 4.98 mm (HD27) ve kök hacmi ise 47.77 cm3 (HD-3) ile 147.54 cm3 (HD-27) arasında değişim göstermiştir. Tüm kök parametreleri birlikte değerlendirildiğinde; toplam kök uzunluğu yönünden HD-16, kök çapı ve kök hacmi değerleri yönünden HD-27, kök yüzey alanı yönünden HD-26 ve kök kuru ağırlığı yönünden ise HD-22 genotipinin ümit var oldukları saptanmıştır.

Seed Characteristics Affect Low-Temperature Stress Tolerance Performance of Rapeseed (Brassica napus L.) during Seed Germination and Seedling Emergence Stages

Screening and breeding elite varieties with rapid germination and uniform seedling emergence under low temperature is an effective strategy to deal with the cold climate occurring under late sowing conditions in the Yangtze River basin. This study focused on the performance of seven functional traits, including percentage of germination, percentage of emergence, mean germination time, mean emergence time, total seedling length, total dry weight, and seedling vigor index of 436 natural rapeseed populations under normal-temperature (25/20 °C) and low-temperature (15/10 °C) conditions. Furthermore, ten genotypes were screened to verify their low-temperature tolerance based on cultivar traits in a pot experiment. The results show that the germination- and emergence-related functional traits of rapeseed genotypes exhibit rich genotypic diversity in response to low-temperature stress; the variation among these traits ranged from 1–25% under normal-temperature and 10–49% under low-temperature conditions. Variation in seed characteristics also affected the capacity for low-temperature tolerance in the process of seed germination and seedling emergence, and could explain 22% of the total variance for low-temperature stress tolerance indices. There existed high correlations between the stress tolerance index of total dry weight (STI_TDW) and thousand-seed weight, and between the stress tolerance index of emergence percentage (STI_PE) and oil content. The contents of erucic acid, glucosinolate, and eicosenoic acid were positively correlated with the stress tolerance index of mean germination time (STI_MGT) and mean emergence time (STI_MET). The D-CRITIC (distance-based intercriteria correlation) weight method was selected in this experiment to calculate each variety’s comprehensive low-temperature stress tolerance index by integrating the standard deviation and distance correlation coefficient of each index. The genotypes with large comprehensive low-temperature stress tolerance index also had higher low-temperature stress tolerance index of biomass and yield in the pot experiment, indicating that the comprehensive low-temperature stress tolerance index has high reliability and applicability. This study could provide a theoretical basis for the utilization of low-temperature-tolerant germplasm resources, as well as a reference for the cold resistance and yield stability under late- and direct-sowing conditions of rapeseed in the Yangtze River basin and other similar environments around the world.

Comparative Transcriptome and Interaction Protein Analysis Reveals the Mechanism of IbMPK3-Overexpressing Transgenic Sweet Potato Response to Low-Temperature Stress.

The sweet potato is very sensitive to low temperature. Our previous study revealed that IbMPK3-overexpressing transgenic sweet potato (M3) plants showed stronger low-temperature stress tolerance than wild-type plants (WT). However, the mechanism of M3 plants in response to low-temperature stress is unclear. To further analyze how IbMPK3 mediates low-temperature stress in sweet potato, WT and M3 plants were exposed to low-temperature stress for 2 h and 12 h for RNA-seq analysis, whereas normal conditions were used as a control (CK). In total, 3436 and 8718 differentially expressed genes (DEGs) were identified in WT at 2 h (vs. CK) and 12 h (vs. CK) under low-temperature stress, respectively, whereas 1450 and 9291 DEGs were detected in M3 plants, respectively. Many common and unique DEGs were analyzed in WT and M3 plants. DEGs related to low temperature were involved in Ca2+ signaling, MAPK cascades, the reactive oxygen species (ROS) signaling pathway, hormone transduction pathway, encoding transcription factor families (bHLH, NAC, and WRKY), and downstream stress-related genes. Additionally, more upregulated genes were associated with the MAPK pathway in M3 plants during short-term low-temperature stress (CK vs. 2 h), and more upregulated genes were involved in secondary metabolic synthesis in M3 plants than in the WT during the long-time low-temperature stress treatment (CK vs. 12 h), such as fatty acid biosynthesis and elongation, glutathione metabolism, flavonoid biosynthesis, carotenoid biosynthesis, and zeatin biosynthesis. Moreover, the interaction proteins of IbMPK3 related to photosynthesis, or encoding CaM, NAC, and ribosomal proteins, were identified using yeast two-hybrid (Y2H). This study may provide a valuable resource for elucidating the sweet potato low-temperature stress resistance mechanism, as well as data to support molecular-assisted breeding with the IbMPK3 gene.

Screening Technique Based on Seed and Early Seedling Parameters for Cold Tolerance of Selected F2-Derived F3 Rice Genotypes under Controlled Conditions

The cold tolerance studies were carried out in a bi-parental F2 population of a cross between tolerant and susceptible parents (SKUA-529 and HEERA, respectively). The purpose was to screen the individuals of a population for primary cold-tolerance-related attributes. The information generated has a direct application and use in identifying cold tolerance quantitative trait loci (QTLs) and further can be used for genotyping with an appropriate marker system. The screening was carried out on F2-derived F3 seeds and F3 plants for seedling and agronomic traits, respectively. Two tests measuring cold tolerance were conducted. In experiment I, seeds were germinated for 28 days at 13 °C and 7 days at 28 °C, and in experiment II, the seeds were germinated for 72 h at 28 °C, 96 h at 13 °C, and once more for 72 h at 28 °C. Coleoptile length, germination percentage, and radical reduction percentages were all measured in experiment I. The radicle and coleoptile regeneration in experiment II were measured after the cold period. The improvement in cold tolerance was achieved through radicle regrowth, as evidenced by the difference between the second and first measurements. The individual lines from the F2:3 population that recorded high germination (%) were #21, #13, #14, and #15. The percentage of coleoptile length (PERCOL %) was observed to be between the ranges of 23.33% to 53.00%. The reduction in coleoptile length (REDCOL %) was also obtained, and there was less reduction in #15, #16, and #14 and it had a range between 38.46% and 75%. Radicle regrowth (REDRAG) was high at 13 °C in #7, #11, #30, #35, and #36. Survival of the seedling range was between 33.33% and up to 100%, and the highest survival rate was observed in #16. The main objective of this rotation in temperature was to emulate field conditions where there has been a drop in temperature. The evaluations were done for primary cold stress tolerance traits, and it was found that most of these traits exhibited high variability. The mapping population developed may be utilized to generate a linkage map and locate QTLs for tolerance to cold stress in rice. Further, the identified donors for cold tolerance may be utilized for breeding programs aimed at the transfer of low-temperature stress tolerance into susceptible backgrounds. In general, a genotype with improved seedling germination rates, growth rates, and leaf yellowing scores; high seedling survival; lesser reduction in coleoptile length and in radicle development; and recovery following a cold shock at the seedling stage demonstrated its cold resistance. Genotypes with a low germination percentage, a greater number of days to germination, slow growth rate and higher leaf yellowing score, high reduction in coleoptile and radicle growth, and reduced seedling survival indicated cold susceptibility.

Genome-Wide Association Mapping Unravels the Genetic Control of Seed Vigor under Low-Temperature Conditions in Rapeseed (Brassica napus L.).

Low temperature inhibits rapid germination and successful seedling establishment of rapeseed (Brassica napus L.), leading to significant productivity losses. Little is known about the genetic diversity for seed vigor under low-temperature conditions in rapeseed, which motivated our investigation of 13 seed germination- and emergence-related traits under normal and low-temperature conditions for 442 diverse rapeseed accessions. The stress tolerance index was calculated for each trait based on performance under non-stress and low-temperature stress conditions. Principal component analysis of the low-temperature stress tolerance indices identified five principal components that captured 100% of the seedling response to low temperature. A genome-wide association study using ~8 million SNP (single-nucleotide polymorphism) markers identified from genome resequencing was undertaken to uncover the genetic basis of seed vigor related traits in rapeseed. We detected 22 quantitative trait loci (QTLs) significantly associated with stress tolerance indices regarding seed vigor under low-temperature stress. Scrutiny of the genes in these QTL regions identified 62 candidate genes related to specific stress tolerance indices of seed vigor, and the majority were involved in DNA repair, RNA translation, mitochondrial activation and energy generation, ubiquitination and degradation of protein reserve, antioxidant system, and plant hormone and signal transduction. The high effect variation and haplotype-based effect of these candidate genes were evaluated, and high priority could be given to the candidate genes BnaA03g40290D, BnaA06g07530D, BnaA09g06240D, BnaA09g06250D, and BnaC02g10720D in further study. These findings should be useful for marker-assisted breeding and genomic selection of rapeseed to increase seed vigor under low-temperature stress.

Thermal Stresses in Maize: Effects and Management Strategies

Climate change can decrease the global maize productivity and grain quality. Maize crop requires an optimal temperature for better harvest productivity. A suboptimal temperature at any critical stage for a prolonged duration can negatively affect the growth and yield formation processes. This review discusses the negative impact of temperature extremes (high and low temperatures) on the morpho-physiological, biochemical, and nutritional traits of the maize crop. High temperature stress limits pollen viability and silks receptivity, leading to a significant reduction in seed setting and grain yield. Likewise, severe alterations in growth rate, photosynthesis, dry matter accumulation, cellular membranes, and antioxidant enzyme activities under low temperature collectively limit maize productivity. We also discussed various strategies with practical examples to cope with temperature stresses, including cultural practices, exogenous protectants, breeding climate-smart crops, and molecular genomics approaches. We reviewed that identified quantitative trait loci (QTLs) and genes controlling high- and low temperature stress tolerance in maize could be introgressed into otherwise elite cultivars to develop stress-tolerant cultivars. Genome editing has become a key tool for developing climate-resilient crops. Moreover, challenges to maize crop improvement such as lack of adequate resources for breeding in poor countries, poor communication among the scientists of developing and developed countries, problems in germplasm exchange, and high cost of advanced high-throughput phenotyping systems are discussed. In the end, future perspectives for maize improvement are discussed, which briefly include new breeding technologies such as transgene-free clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated (Cas)-mediated genome editing for thermo-stress tolerance in maize.

Genome-Wide Identification of Banana Csl Gene Family and Their Different Responses to Low Temperature between Chilling-Sensitive and Tolerant Cultivars.

The cell wall plays an important role in responses to various stresses. The cellulose synthase-like gene (Csl) family has been reported to be involved in the biosynthesis of the hemicellulose backbone. However, little information is available on their involvement in plant tolerance to low-temperature (LT) stress. In this study, a total of 42 Csls were identified in Musa acuminata and clustered into six subfamilies (CslA, CslC, CslD, CslE, CslG, and CslH) according to phylogenetic relationships. The genomic features of MaCsl genes were characterized to identify gene structures, conserved motifs and the distribution among chromosomes. A phylogenetic tree was constructed to show the diversity in these genes. Different changes in hemicellulose content between chilling-tolerant and chilling-sensitive banana cultivars under LT were observed, suggesting that certain types of hemicellulose are involved in LT stress tolerance in banana. Thus, the expression patterns of MaCsl genes in both cultivars after LT treatment were investigated by RNA sequencing (RNA-Seq) technique followed by quantitative real-time PCR (qPCR) validation. The results indicated that MaCslA4/12, MaCslD4 and MaCslE2 are promising candidates determining the chilling tolerance of banana. Our results provide the first genome-wide characterization of the MaCsls in banana, and open the door for further functional studies.

Hydrogen peroxide is involved in strigolactone induced low temperature stress tolerance in rape seedlings (Brassica rapa L.)

Strigolactone (SL) is a plant hormone that can improve plant stress resistance by regulating physiological processes and gene expression. GR24 is a synthetic strigolactone, which can also be used as a plant growth regulator. In this paper, the effects of exogenous GR24 on the growth and development of rape (Brassica rapa L.) under low temperature (4 °C) were studied. The results showed that low temperature (4 °C) inhibited the growth of rape seedlings, and exogenous GR24 significantly alleviated the effect of low temperature stress on rape seedlings. Compared with 4 °C treatment, GR24 + 4 °C treatment can increase the cell viability, soluble protein and proline content, enhance antioxidant enzyme activity, inhibit the production of reactive oxygen species (ROS), improve photosynthesis, and reduce the relative conductivity of rape seedlings. Further research shows that H2O2 plays a central role in improving the cold resistance of rape seedlings by GR24. qRT-PCR results indicated that GR24 significantly increased the expression of genes. Mainly includes antioxidant enzyme genes, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase genes, mitogen-activated protein kinase (MAPK) genes and cold-regulated genes. These results indicate that GR24 improves the cold tolerance of plants by regulating the expression of related genes. RNA-seq analysis revealed that there were 152 differentially expressed genes (DGEs) in T (4 °C)_vs_ST (GR24 + 4 °C), including 100 up-regulated genes and 52 down-regulated genes. These DEGs play an important role in carbon metabolism pathway, oxidative phosphorylation pathway, antioxidant activity and photosynthesis pathways. We selected 11 differentially expressed genes for qRT-PCR verification, and the verification results were consistent with RNA-seq results.