FUNCTIONAL CHARACTERIZATION OF J2 AND J3 CHAPERONES IN THE HEAT STRESS PATHWAY IN ARABIDOPSIS THALIANA

Abstract

Heat waves cause adverse effects on sessile plants, leading to reduced crop productivities. To reduce the complications attributed to heat stress, Arabidopsis J-class heat shock proteins function in the heat shock (HS) response to assist in refolding of denatured proteins. In this study, we have demonstrated that J2 may function redundantly with its homolog J3 as repressors in suppressing HS response during non-HS conditions and are also required for acquired thermotolerance. Both j2 and j3 mutants showed stronger basal thermotolerance than wild-type plants due to the upregulation of HS-responsive genes under non-HS conditions, that is similar to cellular and molecular response of wild-type plants when treated with sublethal HS. Hence, these plants lacking J2 or J3, especially j3 mutants survived better in lethal HS without prior heat acclimatization. J3 is a more crucial repressor than J2 as higher upregulation of HS-responsive genes in j3 mutants are responsible for its better survivability than j2 mutants under basal thermotolerance. On the other hand, J2 and J3 are needed for acquired thermotolerance, probably to attenuate the HS response. The slightly lower survivability of j2 and j3 mutants than wild-type plants in acquired thermotolerance may be due to the derepression of Hsp70s/Hsp90s that subsequently act to repress HsfA1s, which are upstream promoters of J2 and J3.