The transcription factors MYB80 and TEK coordinate callose wall degradation and pollen exine formation in Arabidopsis

Pollen development involves cell wall alteration of the male gametophyte, which is critical for plant fertility and requires MYB80 and TRANSPOSABLE ELEMENT SILENCING VIA AT-HOOK (TEK) transcription factors in Arabidopsis (Arabidopsis thaliana). In this study, we found that the myb80 tek double mutant exhibits a compromised degradation of the tetrad callose wall and down-regulation of five ANTHER-SPECIFIC PROTEIN 6 (A6) genes encoding β-1,3-glucanase. The quintuple mutant of A6 (a6-quint) exhibited delayed callose wall degradation and defective exine structure, and its pollen had a weakened UV resistance. The quadruple mutant of A6 (a6-quad) restored the fertility of rvms-2, a thermo-sensitive genic male sterile (TGMS) line where the transition from tetrad wall to pollen wall is defective. Transgenic expression of A6 and A6.2 driven by the A9 promoter led to the expression of the two genes in the tapetum at earlier anther developmental stages, which caused premature callose wall dissolution and impeded exine formation, indicating the importance of the temporal control of A6s. Furthermore, dual-luciferase and ChIP assay results confirmed the direct regulation of MYB80 and TEK in activating the expression of the above A6s in the tapetum. In conclusion, callose degradation mediated by the MYB80/TEK-A6s pathway is required for the transition from tetrad callose wall to pollen wall.