MKK3-MPK6-MYC2 module positively regulates ABA biosynthesis and signalling in Arabidopsis

Abstract

Involvement of MAPK cascades is well studied in the regulation of ABA mediated responses such as stomatal opening, seed germination and stress tolerance. However most of the studies have focused on ABA signalling and involvement of MAPKs in ABA biosynthesis remains elusive. Hence, in the current study, we have identified the new role of MKK3-MPK6-MYC2 module in positive regulation of ABA biosynthesis as well as ABA responsive genes. Seed germination studies disclosed the ABA insensitive phenotype of myc2, mpk6 and mkk3 mutants. Reduced expression of ABA biosynthesis genes, ABA2 and NCED3 in myc2 and MAPK cascade mutants was confirmed by witnessing the direct binding of MYC2 to the promoter of ABA2 in EMSA assays. Additionally, ABA responsive genes also displayed altered expression patterns in these mutants. Further, transcript and biochemical studies validated the role of MPK6 upstream to MYC2 and downstream to MKK3 in response to ABA. Altogether, we have shown that MKK3-MPK6-MYC2 module induces the expression of several ABA related genes and regulate ABA mediated inhibition of seed germination.