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The dehydration-responsive element binding protein 1 ( DREB1 )/ C-repeat-binding factor ( CBF ) genes are key regulators of cold acclimation and freezing tolerance in the chilling tolerant Arabidopsis thaliana . Here, we investigated the function of three members of the 10 rice DREB1 genes, OsDREB1C , E , and G , in the chilling sensitive rice plants. Their loss of function (LOF) mutants were each more chilling susceptible compared to the wild type, and the LOF mutants of all three genes, dreb1ceg , were more chilling susceptible than any of the single mutants. Strikingly, these mutants were capable of cold acclimation, indicating that these rice DREB1 genes are important for basal chilling tolerance but not cold acclimation. Transcriptome and physiology analyses suggest that the OsDREB1C / E / G genes are involved in reactive oxygen species (ROS) scavenging and cell death regulation under chilling. Furthermore, these three rice DREB1 genes are found to promote tolerance to other abiotic stresses: the OsDREB1C / E / G genes are positive regulators of heat tolerance, OsDREB1C and OsDREB1G are positive regulators of salt tolerance, and OsDREB1G is a positive regulator of drought tolerance. These findings expand our knowledge of the roles of DREB1 proteins in plants, enhance our mechanistic understanding of abiotic stress tolerance and will facilitate the generation of stress-tolerant crop plants.

Rice (Oryza sativa L.) is a chilling-sensitive staple crop that originated in subtropical regions of Asia. Introduction of the chilling tolerance trait enables the expansion of rice cultivation to temperate regions. Here we report the cloning and characterization of HAN1, a quantitative trait locus (QTL) that confers chilling tolerance on temperate japonica rice. HAN1 encodes an oxidase that catalyzes the conversion of biologically active jasmonoyl-L-isoleucine (JA-Ile) to the inactive form 12-hydroxy-JA-Ile (12OH-JA-Ile) and fine-tunes the JA-mediated chilling response. Natural variants in HAN1 diverged between indica and japonica rice during domestication. A specific allele from temperate japonica rice, which gained a putative MYB cis-element in the promoter of HAN1 during the divergence of the two japonica ecotypes, enhances the chilling tolerance of temperate japonica rice and allows it to adapt to a temperate climate. The results of this study extend our understanding of the northward expansion of rice cultivation and provide a target gene for the improvement of chilling tolerance in rice.

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.

• Coordinating stress defense and plant growth is a survival strategy for adaptation to different environments that contains a series of processes, such as, cell growth, division and differentiation. However, little is known about the coordination mechanism for protein conformation change. • A cyclophilin OsCYP20-2 with a variant interacts with SLENDER RICE1 (SLR1) and OsFSD2 in the nucleus and chloroplasts, respectively, to integrate chilling tolerance and cell elongation in rice (Oryza sativa) (FSD2, Fe-superoxide dismutase 2). • Mass spectrum assay showed that OsNuCYP20-2 localized at the nucleus (nuclear located OsCYP20-2) was a new variant of OsCYP20-2 that truncated 71 amino-acid residues in N-terminal. The loss-of function OsCYP20-2 mutant showed sensitivity to chilling stress with accumulation of extra reactive oxygen species (ROS). In chloroplasts, the full-length OsCYP20-2 promotes OsFSD2 forming homodimers which enhance its activity, eliminating the accumulation of ROS under chilling stress. However, the mutant had shorter epidermal cells in comparison with wild-type Hwayoung (HY). In the nucleus, OsCYP20-2 caused conformation change of SLR1 to promote its degradation for cell elongation. • Our data reveal a cyclophilin with a variant with dual-localization in chloroplasts and the nucleus, which mediate chilling tolerance and cell elongation.

Low temperature is a major environmental factor that severely impairs plant growth and productivity. Watermelon ( Citrullus lanatus ) is a chilling-sensitive crop. Grafting of watermelon onto pumpkin rootstock is an effective technique to increase the chilling tolerance of watermelon when exposure to short-time chilling stress. However, the mechanism by which pumpkin rootstock increases chilling tolerance remains poorly understood. Under 10°C/5°C (day/night) chilling stress treatment, pumpkin-grafted watermelon seedlings showed higher chilling tolerance than self-grafted watermelon plants with significantly reduced lipid peroxidation and chilling injury (CI) index. Physiological analysis revealed that pumpkin rootstock grafting led to the notable accumulation of putrescine in watermelon seedlings under chilling conditions. Pre-treat foliar with 1 mM D-arginine (inhibitor of arginine decarboxylase, ADC) increased the electrolyte leakage (EL) of pumpkin-grafted watermelon leaves under chilling stress. This result can be ascribed to the decrease in transcript levels of ADC , ornithine decarboxylase , spermidine synthase , and polyamine oxidase genes involved in the synthesis and metabolism of polyamines. Transcriptome analysis showed that pumpkin rootstock improved chilling tolerance in watermelon seedlings by regulating differential gene expression under chilling stress. Pumpkin-grafted seedling reduced the number and expression level of differential genes in watermelon scion under chilling stress. It specifically increased the up-regulated expression of ADC ( Cla97C11G210580 ), a key gene in the polyamine metabolism pathway, and ultimately promoted the accumulation of putrescine. In conclusion, pumpkin rootstock grafting increased the chilling tolerance of watermelon through transcription adjustments, up regulating the expression level of ADC , and promoting the synthesis of putrescine, which ultimately improved the chilling tolerance of pumpkin-grafted watermelon plants.

Key messageMeJA supplementation enhanced the chilling tolerance and gene expression of PpMsrA1. PpMYB105 protein positively regulated the PpMsrA1 promoter. PpMYB105 mediated the MeJA-boosted chilling tolerance by regulating PpMsrA1.Cold storage can maintain the quality of postharvest fruit. However, peaches easily suffer from chilling injury (CI) during cold storage, leading to economic loss. Results showed that methyl jasmonate (MeJA) supplementation reduced the CI severity, and enhanced the gene expression of methionine sulfoxide reductase A1 (PpMsrA1). It was found that MeJA application elevated the MsrA activity and methionine (Met) content, and reduced the methionine-S-sulfoxide (Met-S-SO) content and reactive oxygen species (ROS) production afterwards. Moreover, PpMYB105 could activate the transcription of PpMsrA1 by binding to the MYB binding element in its promoter. The gene expression of PpMYB105 was up-regulated by MeJA application. Overexpression of PpMYB105 in tomatoes enhanced the chilling tolerance and gene expression of SlMsrA1. Virus-induced gene silencing of PpMYB105 in peaches resulted in the increase in CI severity and the decrease in gene expression of PpMsrA1. Thus, PpMYB105 was involved in the MeJA-boosted chilling tolerance by regulating PpMsrA1.

Rice ( L.) is often exposed to cool temperatures during spring planting in temperate climates. A better understanding of genetic pathways regulating chilling tolerance will enable breeders to develop varieties with improved tolerance during germination and young seedling stages. To dissect chilling tolerance, five assays were developed; one assay for the germination stage, one assay for the germination and seedling stage, and three for the seedling stage. Based on these assays, five chilling tolerance indices were calculated and assessed using 202 accessions from the Rice Mini-Core (RMC) collection. Significant differences between RMC accessions made the five indices suitable for genome-wide association study (GWAS) based quantitative trait loci (QTL) mapping. For young seedling stage indices, and subspecies clustered into chilling tolerant and chilling sensitive accessions, respectively, while both subspecies had similar low temperature germinability distributions. subspecies were shown to have chilling acclimation potential. GWAS mapping uncovered 48 QTL at 39 chromosome regions distributed across all 12 rice chromosomes. Interestingly, there was no overlap between the germination and seedling stage QTL. Also, 18 QTL and 32 QTL were in regions discovered in previously reported bi-parental and GWAS based QTL mapping studies, respectively. Two novel low temperature seedling survivability (LTSS)-QTL, and , were not in a previously reported QTL region. QTL with strong effect alleles identified in this study will be useful for marker assisted breeding efforts to improve chilling tolerance in rice cultivars and enhance gene discovery for chilling tolerance.

Low temperature is a significant environmental constraint, impeding the extensive cultivation of tropical plants. Here, we identify the transcription factor SlMYB17 as an important negative regulator of tomato chilling tolerance. Overexpression of SlMYB17 significantly reduced chilling tolerance, whereas slmyb17 mutants exhibited enhanced tolerance. ChIP‐seq analysis revealed that SlMYB17 targets genes involved in diverse biological processes and stress responses, suggesting its role in coordinating plant development and stress adaptation. SlMYB17 directly binds to the promoters of cold‐regulated (COR) genes, such as SlCOR27b and WCOR413, thereby inhibiting their expression. Crucially, protein–protein interaction studies and Dual‐LUC assays demonstrated that SlMYB17 interacts with SlCBF1, SlCBF2, and SlCBF3 in the nucleus to inhibit SlCBF‐mediated activation of COR genes. Using virus‐induced gene silencing (VIGS) targeting SlCBF1‐3 in wild‐type and slmyb17 mutants, we demonstrate genetically that SlMYB17's function in chilling tolerance is dependent on SlCBFs. Collectively, SlMYB17 antagonises the SlCBF pathway at both transcriptional and protein activity levels, ultimately suppressing tomato chilling tolerance. Our work establishes slmyb17 mutants as valuable genetic resources for developing chilling‐tolerant tomato varieties, and the ChIP‐seq data provide important insights for studying MYB transcription factors in stress responses and development.

Chilling stress is an important constraint for maize seedling establishment in the field. To examine the role of salicylic acid (SA) and hydrogen peroxide (H2O2) in response to chilling stress, we investigated the effects of seed priming with SA, H2O2, and SA+H2O2 combination on maize resistance under chilling stress (13°C). Priming with SA, H2O2, and especially SA+H2O2 shortened seed germination time and enhanced seed vigor and seedling growth as compared with hydropriming and non-priming treatments under low temperature. Meanwhile, SA+H2O2 priming notably increased the endogenous H2O2 and SA content, antioxidant enzymes activities and their corresponding genes ZmPAL, ZmSOD4, ZmAPX2, ZmCAT2 , and ZmGR expression levels. The α-amylase activity was enhanced to mobilize starch to supply metabolites such as soluble sugar and energy for seed germination under chilling stress. In addition, the SA+H2O2 combination positively up-regulated expressions of gibberellic acid (GA) biosynthesis genes ZmGA20ox1 and ZmGA3ox2 , and down-regulated GA catabolism gene ZmGA2ox1 expression; while it promoted GA signaling transduction genes expressions of ZmGID1 and ZmGID2 and decreased the level of seed germination inhibitor gene ZmRGL2 . The abscisic acid (ABA) catabolism gene ZmCYP707A2 and the expressions of ZmCPK11 and ZmSnRK2.1 encoding response receptors in ABA signaling pathway were all up-regulated. These results strongly suggested that priming with SA and H2O2 synergistically promoted hormones metabolism and signal transduction, and enhanced energy supply and antioxidant enzymes activities under chilling stress, which were closely relevant with chilling injury alleviation and chilling-tolerance improvement in maize seed.Highlights: Seed germination and seedling growth were significantly improved under chilling stress by priming with SA+H2O2 combination, which was closely relevant with the change of reactive oxygen species, metabolites and energy supply, hormones metabolism and regulation.