The Arabidopsis ARID-HMG protein AtHMGB15 modulates JA signalling by regulating MYC2 during pollen development

In flowering plants, jasmonic acid (JA) signalling regulates the complex process of male gametophyte development. JA signalling initiates with the activation of MYC2 transcription factor, for the expression of several JA responsive genes throughout stamen development and pollen maturation. However, the regulation of JA signalling during different developmental stages of male gametophytes is still less understood. In this study we have characterized T-DNA insertion line of AtHMGB15. Phenotypic characterization of athmgb15-4 mutant plants showed delayed bolting, shorter siliques and reduced seed set compared to wildtype. Moreover, deletion of AtHMGB15 resulted in defective pollen morphology, delayed pollen germination, abberant pollen tube growth and a higher percentage of non-viable pollen population in athmgb15-4 compared to wildtype. Molecular analysis indicated down-regulation of JA-biosynthesis and JA-signalling genes viz MYC2, MYB21 and MYB24 in athmgb15-4 mutant. Furthermore, jasmonic acid and its derivatives were found almost ten-fold lower in athmgb15-4 flowers. However, exogenous application of jasmonate could restore pollen morphology and pollen germination, suggesting that impaired JA signalling is responsible for the pollen phenotype in athmgb15 mutant. AtHMGB15 physically interacts with MYC2 protein to form the transcription activation complex for promoting transcription of genes responsible for JA signalling during stamen and pollen development. Collectively, our findings indicate that AtHMGB15, a plant specific DNA binding protein of the ARID-HMG group, acts as a positive regulator of JA signalling to control the spatiotemporal expression of key regulators responsible for stamen and pollen development.