A Cystathionine-β-Synthase Domain-Containing Protein, CBSX2, Regulates Endothecial Secondary Cell Wall Thickening in Anther Development

Anther formation and dehiscence are complex pivotal processes in reproductive development. The secondary wall thickening in endothecial cells of the anther is a known prerequisite for successful anther dehiscence. However, many gaps remain in our understanding of the regulatory mechanisms underlying anther dehiscence in planta, including a possible role for jasmonic acid (JA) and H2O2 in secondary wall thickening of endothecial cells. Here, we report that the cystathionine beta-synthase domain-containing protein CBSX2 located in the chloroplast plays a critical role in thickening of the secondary cell walls of the endothecium during anther dehiscence in Arabidopsis. A T-DNA insertion mutant of CBSX2 (cbsx2) showed increased secondary wall thickening of endothecial cells and early anther dehiscence. Consistently, overexpression of CBSX2 resulted in anther indehiscence. Exogenous JA application induced secondary wall thickening and caused flower infertility in the cbsx2 mutant, whereas it partially restored fertility in the CBSX2-overexpressing lines lacking the wall thickening. CBSX2 directly modulated thioredoxin (Trx) in chloroplasts, which affected the level of H2O2 and, consequently, expression of the genes involved in secondary cell wall thickening. Our findings have revealed that CBSX2 modulates the H2O2 status, which is linked to the JA response and in turn controls secondary wall thickening of the endothecial cells in anthers for dehiscence to occur.