Heat Shock Proteins atHSP93-III and atHSP93-V Affect ABA Response and Leaf Senescence
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We carried out activation tagging screen to isolate ABA signaling components and isolated an ABAhypersensitive mutant, ahs716 (ABA-hypersensitive 716). TDNA was inserted in the 5’ flanking region of the atHSP93-III gene in the mutant, and the atHSP93-III transcript level was barely detectable, indicating that it is a knockdown mutant. The mutant exhibited poor viability, and, therefore, we prepared and analyzed its overexpression (OX) lines to study its function. Plants overexpressing atHSP93-III were hypersensitive to ABA, and several ABA-regulated genes were up-regulated in the transgenic plants. We also investigated the role of atHSP93-V in ABA response. atHSP93-V is a paralog of atHSP93-III and encodes an isoform of HSP93. Although it is highly homologous to atHSP93-III, atHSP93-V OX did not affect ABA sensitivity. However, the atHSP93-V OX lines displayed early senescence phenotype, and changes in the expression levels of several senescence-related genes were observed in the transgenic lines. Collectively, our data suggest that, whereas atHSP93-V is involved in leaf senescence, atHSP93-III is involved in ABA response. Considering that HSP93 is a molecular chaperone essential for chloroplast biogenesis and function, the resuls provide evidence that chloroplast function is important for normal ABA response.
KeywordsAbscisic acid (ABA) Chaperone Hsp93 Senescence
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