SWOLLEN TAPETUM AND STERILITY 1 is required for tapetum degeneration and pollen wall formation in rice

The pollen wall is important for protecting the male gametophyte and for fertilization. The lipid components of the pollen wall are mainly synthesized and transported from the sporophytic tapetum. Although several factors related to lipid biosynthesis have been characterized, the molecular mechanisms underlying lipid biosynthesis during pollen development in rice (Oryza sativa L.) remain elusive. Here, we showed that mutation in the SWOLLEN TAPETUM AND STERILITY 1 (STS1) gene causes delayed tapetum degradation and aborted pollen wall formation in rice. STS1 encodes an endoplasmic reticulum (ER)-localized protein that contains domain of unknown function (DUF) 726 and exhibits lipase activity. Lipidomic and transcriptomic analyses showed that STS1 is involved in anther lipid homeostasis. Moreover, STS1 interacts with Polyketide Synthase 2 (OsPKS2) and Acyl-CoA Synthetase 12 (OsACOS12), two enzymes crucial in lipidic sporopollenin biosynthesis in pollen wall formation, suggesting a potentially lipidic metabolon for sporopollenin biosynthesis in rice. Collectively, our results indicate that STS1 is an important factor for lipid biosynthesis in reproduction, providing a target for the artificial control of male fertility in hybrid rice breeding and insight into the function of DUF726-containing protein in plants.