Plant physiology 2016
A rice Ca2+ binding protein is required for tapetum function and pollen formation.
In flowering plants, successful male reproduction requires the sophisticated interaction between somatic anther wall layers and reproductive cells. Timely degradation of the innermost tissue of the anther wall layer, tapetal layer, is critical for pollen development. Ca2+ is a well-known stimulus for plant development, however, whether it plays a role in affecting male reproduction remains elusive. Here we report a role of OsDEX1 (Defective in Exine Formation 1 in rice), a Ca2+ binding protein, in regulating rice tapetal cell degradation and pollen formation. In osdex1 anthers, tapetal cell degeneration is delayed and degradation of the callose wall surrounding the microspores is compromised, leading to aborted pollen formation and complete male sterility. OsDEX1 transcript is observed in tapetal cells and microspores during the early anther development. Recombinant OsDEX1 is able to bind Ca2+ and regulate Ca2+ homeostasis in vitro, and osdex1 showed disturbed Ca2+ homeostasis in tapetal cells. Phylogenetic analysis revealed that OsDEX1 may have a conserved function in binding Ca2+ in flowering plants, and genetic complementation of pollen wall defects in an Arabidopsis dex1 mutant confirmed its evolutionary conservation during pollen development. Collectively, these findings suggest that OsDEX1 plays a conserved role in the development of tapetal cells and pollen formation, possibly via changing the Ca2+ homeostasis during pollen development.