Despite our increasing knowledge on the transcriptional networks connecting abscisic acid (ABA) signalling with the circadian clock, the molecular nodes in which both pathways converge to translate the environmental information into a physiological response are not known. Here, we provide evidence of a feedback mechanism linking the circadian clock with plant responses to drought. A key clock component (TOC1, timing of CAB expression 1) binds to the promoter of the ABA-related gene (ABAR/ CHLH/GUN5) and controls its circadian expression. TOC1 is in turn acutely induced by ABA and this induction advances the phase of TOC1 binding and modulates ABAR circadian expression. Moreover, the gated induction of TOC1 by ABA is abolished in ABAR RNAi plants suggesting that the reciprocal regulation between ABAR and TOC1 expression is important for sensitized ABA activity. Genetic studies with TOC1 and ABAR over-expressing and RNAi plants showed defective responses to drought, which support the notion that clock-dependent gating of ABA function is important for cellular homeostasis under dry environments.

Environmental stresses are the major cause of crop loss worldwide. Polyamines are involved in plant stress responses. However, the precise role(s) of polyamine metabolism in these processes remain ill-defined. Transgenic approaches demonstrate that polyamines play essential roles in stress tolerance and open up the possibility to exploit this strategy to improve plant tolerance to multiple environmental stresses. The use of Arabidopsis as a model plant enables us to carry out global expression studies of the polyamine metabolic genes under different stress conditions, as well as genome-wide expression analyses of insertional-mutants and plants over-expressing these genes. These studies are essential to dissect the polyamine mechanism of action in order to design new strategies to increase plant survival in adverse environments.

PRMT5Premature Stop Codon (prmt5-5) PRMT5 PRMT5Premature

The levels of endogenous polyamines have been shown to increase in plant cells challenged with low temperature; however, the functions of polyamines in the regulation of cold stress responses are unknown. Here, we show that the accumulation of putrescine under cold stress is essential for proper cold acclimation and survival at freezing temperatures because Arabidopsis (Arabidopsis thaliana) mutants defective in putrescine biosynthesis (adc1, adc2) display reduced freezing tolerance compared to wild-type plants. Genes ADC1 and ADC2 show different transcriptional profiles upon cold treatment; however, they show similar and redundant contributions to cold responses in terms of putrescine accumulation kinetics and freezing sensitivity. Our data also demonstrate that detrimental consequences of putrescine depletion during cold stress are due, at least in part, to alterations in the levels of abscisic acid (ABA). Reduced expression of NCED3, a key gene involved in ABA biosynthesis, and down-regulation of ABA-regulated genes are detected in both adc1 and adc2 mutant plants under cold stress. Complementation analysis of adc mutants with ABA and reciprocal complementation tests of the aba2-3 mutant with putrescine support the conclusion that putrescine controls the levels of ABA in response to low temperature by modulating ABA biosynthesis and gene expression.