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The contribution of glutathione (GSH) in combating environmental stress in plants has long been known. Previous reports have pointed to the involvement of GSH in inducing various heat shock proteins (HSPs), but the molecular mechanism is yet to be explored. Here, we investigate how GSH induces the expression of important HSP genes in Arabidopsis. Expression of HSP genes BiP3, HSP70B, and HSP90.1 was positively regulated by GSH, and a promoter activation assay suggested a role for GSH in their induction. Lower expression of BiP3 and HSP70B in the GSH-fed Atmyb21 mutant and of HSP90.1 in the GSH-fed Atbzip10 mutant, in comparison with GSH-fed Col-0, revealed a role for GSH in activating their promoters through the transcription factors MYB21 and BZIP10. Co-transfection of transcription factor mutant protoplasts with transcription factor constructs and HSP promoters confirmed the results. Comparative proteomics also revealed proteins whose expression was controlled by MYB21 and BZIP10 in response to GSH feeding. A co-immunoprecipitation assay demonstrated a role for GSH in modulating the level of interaction of glutathione-S-transferase with HSP70. Collectively, our results demonstrate a role for GSH in activating the promoters of BiP3 and HSP70B via MYB21 and of HSP90.1 via BZIP10. [ABSTRACT FROM AUTHOR]

Glutathione (GSH) plays a fundamental role in plant defense-signaling network. Recently, we have established the involvement of GSH with ethylene (ET) to combat environmental stress. However, the mechanism of GSH-ET interplay still remains unexplored. Here, we demonstrate that GSH induces ET biosynthesis by modulating the transcriptional and posttranscriptional regulations of its key enzymes, 1-aminocyclopropane-1-carboxylate synthase (ACS) and 1-aminocyclopropane-1-carboxylate oxidase (ACO). Transgenic Arabidopsis (Arabidopsis thaliana) plants with enhanced GSH content (AtECS) exhibited remarkable up-regulation of ACS2, ACS6, and ACO1 at transcript as well as protein levels, while they were down-regulated in the GSH-depleted phytoalexin deficient2-1 (pad2-1) mutant. We further observed that GSH induced ACS2 and ACS6 transcription in a WRKY33-dependent manner, while ACO1 transcription remained unaffected. On the other hand, the messenger RNA stability for ACO1 was found to be increased by GSH, which explains our above observations. In addition, we also identified the ACO1 protein to be a subject for S-glutathionylation, which is consistent with our in silico data. However, S-glutathionylation of ACS2 and ACS6 proteins was not detected. Further, the AtECS plants exhibited resistance to necrotrophic infection and salt stress, while the pad2-1 mutant was sensitive. Exogenously applied GSH could improve stress tolerance in wild-type plants but not in the ET-signaling mutant ethylene insensitive2-1, indicating that GSH-mediated resistance to these stresses occurs via an ET-mediated pathway. Together, our investigation reveals a dual-level regulation of ET biosynthesis by GSH during stress. [ABSTRACT FROM AUTHOR]