Functional Redundancy of ZmSWEET6a/b in Mediating Sugar Transport and Redox Homeostasis for Maize Primexine Formation

Male gametophyte development in maize requires precise coordination of carbohydrate allocation, yet the molecular mechanisms linking sugar transport to early pollen wall formation remain poorly understood. Although sugar transporters, particularly SWEET family members, are known to regulate male fertility in Arabidopsis and rice, their roles in maize microsporogenesis--especially in primexine assembly and redox homeostasis--have not been functionally characterized. Here, we identify two anther-specific Clade II SWEET genes, ZmSWEET6a and ZmSWEET6b, encoding redundant plasma membrane hexose transporters. Loss of both genes leads to complete male sterility, accompanied by disrupted deposition of primexine polysaccharides (pectin and xylan), premature accumulation of reactive oxygen species (ROS), and ectopic programmed cell death (PCD) in the tapetum. We demonstrate that ZmSWEET6a/b-mediated hexose transport is essential for maintaining sugar homeostasis and redox balance during early microsporogenesis. These findings establish a direct mechanistic link between sugar transport, ROS signaling, and pollen wall development in maize, providing new insights into the integration of metabolic and developmental pathways during plant reproduction.