The expression of KCS6 in endothecium persist much later than KCS7/15/21 in tapetum during anther development
Our recent work showed that KCS6 interacts with CER2/CER2L2 for pollen coat very-long-chain fatty acids (VLCFAs) synthesis required for pollen hydration (Zhan et al., 2018). Therefore, both KCS6 in endothecium and KCS7/15/21 in tapetum contribute to the synthesis of pollen coat lipids. Currently no efficient techniques are available to distinguish the difference of lipids synthesized by the tapetum and endothecium. We compared the expression of KCS and CER proteins during anther development to understand the accumulation of the lipids in pollen coat. In previous work, we obtained transgenic lines ofpKCS6::KCS6-GFP , pCER2::CER2-GFP andpCER2L2::CER2L2-GFP (Zhan et al., 2018). All the GFP transgenic plants were grown in the same pot and cultured in the same condition. The expression of KCS6, CER2 and CER2L2 displayed a long period in endothecium from anther stage 8 to 12 (Fig. 5a). KCS7, KCS15 and KCS21 were expressed in tapetum (stage 8 to 10) (Fig. 1,5). They displayed a shorter time period than KCS6, CER2 and CER2L2 (Fig. 5a). These results not only suggested the different functions between KCS7/15/21 and KCS6 in anther development, but also indicating the different roles of tapetum- and endothecium-derived lipids. Tapetum-derived lipids may synthesize and deposited in pollen coat much earlier than endothecium-derived lipids. MS1 protein accumulates in tapetal cells at anther stage 7 and stage 8 (Yang, Vizcay-Barrena, Conner, & Wilson, 2007), overlapping with that of KCS7, KCS15 and KCS21 (Fig. 5a), further indicating that the expression of KCS7 , KCS15 andKCS21 were regulated by MS1 (Fig. 2).