MOLECULAR MECHANISMS OF PLANT RESPONSES TO COLD, HEAT AND SALT STRESSES IN ARABIDOPSIS
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Abiotic stresses, such as temperature extremes and salinity adversely affect plant productivity and distribution worldwide. Resistant or susceptible to stresses is a complex trait because more than one stress may occur simultaneously, for example, salinity is accompanied with ion toxicity and water deficit. To survive in a fixed environment, plants have to adjust their metabolisms and developmental programs to adapt to the stress or acclimate to the transitory stress. The responses of plants to different abiotic stresses are extremely complex, involving stress perception, signaling transduction, and response induction. We took a forward genetic analysis approach and identified three novel proteins in the reference plant Arabidopsis thaliana, Regulator of CBF Gene Expression 1 (RCF1), Regulator of CBF Gene Expression 3 (RCF3), and Short Root in Salt Medium 3 (RSA3), which are critical for plant tolerance to cold, heat and salinity, respectively. RCF1 is a cold-inducible DEAD box RNA helicase protein which is localized in the nucleus. RCF1 is a positive regulator for chilling and freezing tolerance. RCF1 functions to maintain proper splicing of pre-mRNAs because many cold-responsive genes are mis-spliced in rcf1-1 mutant plants under cold stress. RCF3 encodes a KH-domain containing putative RNA-binding protein. RCF3 is a negative regulator of most heat stress transcription factors (HSFs). Consistent with the overall increased accumulation of heat-responsive genes, the rcf3 mutants are heat-tolerant. RSA3, a xylogluscan galactosyltransferase, is essential for salt stress tolerance. rsa3-1 mutant plants are hypersensitive to NaCl and LiCl but not to CsCl or to general osmotic stress. RSA3 controls expression of many genes including genes encoding proteins for reactive oxygen species (ROS) detoxification under salt stress. RSA3 functions to maintaining the proper organization of actin microfilaments in order to minimize damage caused by excessive ROS. miRNAs play important regulatory roles in plants by targeting messenger RNAs (mRNAs) for cleavage or translational repression. We determined role of the heat-inducible miR398 in plant heat stress tolerance. Our results suggest that plants use a previously unrecognized strategy to achieve thermotolerance, especially for the protection of reproductive tissues. This strategy involves the down-regulation of two copper/zinc superoxide dismutase (CSDs) and their copper chaperone CCS through the heat-inducible miR398.