OsPAD1, encoding a non-specific lipid transfer protein, is required for rice pollen aperture formation

Plant lipid transfer proteins (LTPs) are distinguished by their capacity to facilitate lipid transport in vitro between membranes. This includes the transportation of lipid constituents from the tapetum to the microspore, thereby playing a pivotal role in the synthesis and construction of the pollen wall, encompassing the formation of the pollen aperture. However, our understanding of LTPs and their role in pollen aperture formation in rice remains limited. In this study, we have isolated and characterized a male sterile rice mutant named as pollen aperture defect 1 (Ospad1). When compared to the wild type, Ospad1 mutant plants exhibit pollen grain abortion due to the absence of the fibrillar-granular layer, ultimately leading to the leakage of contents from the malformed aperture. OsPAD1 encodes a non-specific LTP and is specifically expressed in the microspore during male development. Subsequently, in vitro lipid binding assays reveal that the recombinant OsPAD1 protein has the capability to bind to a broad spectrum of lipids. The malfunction of OsPAD1 results in disrupted lipid metabolism and compromised pollen aperture, ultimately leading to male sterility. Furthermore, yeast two-hybrid, bimolecular fluorescent complementation and pull-down assays all demonstrate that OsPAD1 can directly interact with OsINP1, an orthologue of a crucial aperture factor in Arabidopsis, together regulating rice aperture development. These findings offer new insights into the molecular mechanisms that underlie the function of LTPs in rice pollen aperture formation. This research holds potential implications not only for rice but also for other cereal crops.