Arabidopsis SOMATIC EMBRYOGENESIS RECEPTOR KINASES1 and 2 Are Essential for Tapetum Development and Microspore Maturation W OA

Among the >200 members of the leucine-rich repeat receptor kinase family in Arabidopsis thaliana, only a few have been functionally characterized. Here, we report a critical function in anther development for the SOMATIC EMBRYOGENESIS RECEPTOR KINASE1 (SERK1) and SERK2 genes. Both SERK1 and SERK2 are expressed widely in locules until stage 6 anthers and are more concentrated in the tapetal cell layer later. Whereas serk1 and serk2 single insertion mutants did not show developmental phenotypes, serk1 serk2 double mutants were not able to produce seeds because of a lack of pollen development in mutant anthers. In young buds, double mutant anthers developed normally, but serk1 serk2 microsporangia produced more sporogenous cells that were unable to develop beyond meiosis. Furthermore, serk1 serk2 double mutants developed only three cell layers surrounding the sporogenous cell mass, whereas wild-type anthers developed four cell layers. Further confocal microscopic and molecular analyses showed that serk1 serk2 double mutant anthers lack development of the tapetal cell layer, which accounts for the microspore abortion and male sterility. Taken together, these findings demonstrate that the SERK1 and SERK2 receptor kinases function redundantly as an important control point for sporophytic development controlling male gametophyte production.