Transcriptional regulation and signalling of cold stress response in plants: An overview of current understanding

Seed priming is a pre-germination treatment administered through various chemical, physical and biological agents, which induce mild stress during the early phases of germination. Priming facilitates synchronized seed germination, better seedling establishment, improved plant growth and enhanced yield, especially in stressful environments. In parallel, the phenomenon of 'stress memory' in which exposure to a sub-lethal stress leads to better responses to future or recurring lethal stresses has gained widespread attention in recent years. The versatility and realistic yield gains associated with seed priming and its connection with stress memory make a critical examination useful for the design of robust approaches for maximizing future yield gains. Herein, a literature review identified selenium, salicylic acid, poly-ethylene glycol, CaCl2 and thiourea as the seed priming agents (SPRs) for which the most studies have been carried out. The average priming duration for SPRs generally ranged from 2 to 48 h, i.e. during phase I/II of germination. The major signalling events for regulating early seed germination, including the DOG1 (delay of germination 1)-abscisic acid (ABA)-heme regulatory module, ABA-gibberellic acid antagonism and nucleus-organelle communication are detailed. We propose that both seed priming and stress memory invoke a 'bet-hedging' strategy in plants, wherein their growth under optimal conditions is compromised in exchange for better growth under stressful conditions. The molecular basis of stress memory is explained at the level of chromatin reorganization, alternative transcript splicing, metabolite accumulation and autophagy. This provides a useful framework to study similar mechanisms operating during seed priming. In addition, we highlight the potential for merging findings on seed priming with those of stress memory, with the dual benefit of advancing fundamental research and boosting crop productivity. Finally, a roadmap for future work, entailing identification of SPR-responsive varieties and the development of dual/multiple-benefit SPRs, is proposed for enhancing SPR-mediated agricultural productivity worldwide.

Seed 'primeomics': plants memorize their germination under stress

Plants are exposed to various abiotic stresses and there exists sophisticated mechanisms within them for tolerating these stresses. The present study clearly revealed the efficacy of UV-B priming at both seed and seedling stage in tolerant (Kanchana) and sensitive (Aiswarya) rice varieties, to tolerate UV-B stress, polyethylene glycol-6000 (PEG) and NaCl stresses. Increase in UV stress specific characters such as accumulation of UV absorbing compounds [flavonoids (242–368%) and anthocyanin (367–386%) content],increased activity of phenylalanine ammonia lyase (116–210%) and increased leaf cuticular wax content (382–403%) was observed in UV-B primed seedlings of rice subjected to UV-B, NaCl and PEG stresses. The increase in the levels shown as percent increase were highest in seedlings subjected to UV-B stress followed by NaCl and PEG stresses. The influence of priming imprints was more effective in seeds and seedlings of the tolerant rice variety (Kanchana) than the sensitive variety (Aiswarya). Functional groups variation in wax content was more prominent in PEG stress conditions than UV-B and NaCl stresses and it was mainly observed in Aiswarya than in Kanchana. Additionally our results suggests the UV-priming mediated enhancement of the stress tolerance potential of a tolerant variety seems to be more successful than the sensitive variety.

UV-B priming enhances specific secondary metabolites in Oryza sativa (L.) empowering to encounter diverse abiotic stresses

The footprint of tomato cultivation, a cool region crop that exhibits heat stress (HS) sensitivity, is increasing in the tropics/sub-tropics. Knowledge of novel regulatory hot spots from varieties growing in the Indian sub-continent climatic zones could be vital for developing HS-resilient crops. Comparative transcriptome-wide signatures of a tolerant (CLN1621L) and sensitive (CA4) cultivar pair shortlisted from a pool of varieties exhibiting variable thermo-sensitivity using physiological-, survival- and yield-related traits revealed redundant to cultivar-specific HS regulation. The antagonistically expressing genes encode enzymes and proteins that have roles in plant defence and abiotic stresses. Functional characterization of three antagonistic genes by overexpression and silencing established Solyc09g014280 (Acylsugar acyltransferase) and Solyc07g056570 (Notabilis) that are up-regulated in tolerant cultivar, as positive regulators of HS tolerance and Solyc03g020030 (Pin-II proteinase inhibitor), that are down-regulated in CLN1621L, as negative regulator of thermotolerance. Transcriptional assessment of promoters of these genes by SNPs in stress-responsive cis-elements and promoter swapping experiments in opposite cultivar background showed inherent cultivar-specific orchestration of transcription factors in regulating transcription. Moreover, overexpression of three ethylene response transcription factors (ERF.C1/F4/F5) also improved HS tolerance in tomato. This study identifies several novel HS tolerance genes and provides proof of their utility in tomato thermotolerance.

Characterization of novel regulators for heat stress tolerance in tomato from Indian sub-continent.

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Dissecting postharvest chilling injury through biotechnology.

HY5, a bZIP transcription factor, plays a key role in the light- and cold-stress signaling pathways. In this study, the tomato HY5 gene (SlHY5) was isolated and characterized with respect to its function in cold-stress tolerance. The expression level of SlHY5 was similar in the root, stem, leaf, flower, and fruit of tomato. SlHY5 was upregulated gradually during cold stress and was induced in response to NaCl and the plant hormone abscisic acid. Overexpression of SlHY5 in tomato markedly increased cold stress tolerance. In addition, the SlHY5-overexpressing lines exhibited enhanced expression of genes related to antioxidant defense systems (SOD and CAT) and anthocyanin biosynthesis (CHS, CHI, and F3H) under cold stress compared to the wild-type plants, which suggested that overexpression of SlHY5 alleviated oxidative damage and lipid peroxidation, relieved membrane injuries induced by cold stress, enhanced anthocyanin accumulation, and thereby enhanced the cold-stress tolerance of SlHY5-overexpressing tomato plants. Furthermore, SlHY5 was involved in the regulation of several cold-induced genes, including PR1, CYSb, LEA, Osmotin, and ICE1, suggesting that constitutive overexpression of SlHY5 in tomato modulates the expression of other stress-responsive genes, thereby imparting cold tolerance. In conclusion, these results indicate that SlHY5 enhances plant tolerance to cold stress and that it may be used to facilitate the enhancement of stress tolerance in tomato.

SlHY5 is a necessary regulator of the cold acclimation response in tomato

Plasma membrane intrinsic protein SlPIP1;7 promotes root growth and enhances drought stress tolerance in transgenic tomato (Solanum lycopersicum) plants

Nani Han

Papers

SlHY5 is a necessary regulator of the cold acclimation response in tomato

Plasma membrane intrinsic protein SlPIP1;7 promotes root growth and enhances drought stress tolerance in transgenic tomato (Solanum lycopersicum) plants