Overexpressing OsFBN1 enhances plastoglobule formation, reduces grain-filling percent and jasmonate levels under heat stress in rice

Abstract

In higher plants, Fibrillins (FBNs) constitute a conserved plastid-lipid-associated (PAPs) protein family and modulate the metabolite transport and lipid metabolism in plastids of dicot species. However, FBNs have not functionally characterized in monocot species. In this study, the function of rice fibrillin 1 (OsFBN1) was investigated. The subcellular localization assay showed that the N-terminal chloroplast transport peptide (CTP) could facilitate the import of OsFBN1 into chloroplast. OsFBN1 specifically bound C18- and C20- fatty acids in vitro. Overexpressing OsFBN1 increased the tiller number but decreased the panicle length, grain-filling percent and JA levels compared to the wild type and RNAi silencing lines under heat stress. In addition, the overexpressing lines had more plastoglobules (PGs) than the wild type and RNAi silencing lines under both normal and heat stress conditions. Moreover, overexpressing OsFBN1 affected the transcription levels of OsAOS2 in JA synthesis, OsTHF1, OsABC1K7 and OsPsaE in thylakoid stability and photosynthesis, OsABC1-4 and OsSPS2 in ubiquinone-metabolism, OsHDR, OsDXR, and OsFPPS in isoprenoid metabolism. Collectively, these findings suggest the essential role of rice OsFBN1 in PG formation and lipid metabolism in chloroplasts, which coordinately regulate the growth and grain filling of the overexpressing lines under heat stress.