Iron–sulfur cluster biosynthesis protein OsSUFD is essential for chloroplast function and environmental adaptation in rice

Abstract

Iron–sulfur (Fe–S) clusters are essential cofactors for diverse biological processes, and their biosynthesis in chloroplasts is mediated by the evolutionarily conserved sulfur utilization factor (SUF) pathway. However, the molecular composition of the rice (Oryza sativa L., Os) SUF system and its roles in chloroplast biology and environmental stress adaptation remain unclear. Here, we report that mutations in the rice homolog of bacterial and plant SUFD, designated OsSUFD, lead to defective chloroplast development and premature leaf senescence. Biochemical analyses show that OsSUFD presumably assembles with OsSUFB and OsSUFC to form a chloroplastic scaffold complex. Notably, OsSUFC also interacts with a chloroplastic DNAJ chaperone, a potential iron donor for Fe–S cluster biosynthesis. Consistent with these observations, mutations in OsSUFD disrupt iron homeostasis and reduce the accumulation of plastidial Fe–S proteins. Furthermore, impaired OsSUFD function compromises rice tolerance to oxidative and heat stresses, accompanied by increased reactive oxygen species accumulation and decreased chlorophyll levels. In contrast, overexpression of OsSUFD in rice enhances tolerance to these abiotic stresses and alleviates the stress-induced physiological damage, further confirming its functional role in stress responses. Collectively, our findings define the conserved architectural features of the rice SUF system and reveal its essential roles in Fe–S cluster biogenesis, chloroplast function maintenance, and environmental stress tolerance.