Identification of SMS1, a UGPase protein gene that regulates programmed cell death, cell wall formation and pollen development in rice

Programmed cell death (PCD) plays an essential role in plant development and response to environmental stimuli. However, the underlying molecular regulatory mechanisms are largely unknown. In this study, we investigated the roles of the SMS1 gene to dissect its molecular mechanisms in rice PCD. The SMS1 gene was characterized by map-based cloning. Functional prediction and verification of the SMS1 gene were further conducted through complementation tests, subcellular localization assays, tissue-specific gene expression using GUS staining, and overexpression analysis using real-time quantitative RT-PCR. The sms1 mutant showed constitutive PCD, defective cell wall structure, and reduced pollen sterility. SMS1 encodes a uridine diphosphate glucose pyrophosphorylase (UGPase). SMS1 is ubiquitously expressed in rice, and the SMS1 protein localizes to both the cytoplasm and nucleus, implying a fundamental and crucial role in various rice tissues. Taken together, we demonstrate that by modulating UDP-glucose metabolism, SMS1 contributes to the maintenance of cell wall organization and cell viability in rice, providing, for the first time, evidence that sugar homeostasis regulates plant PCD.