Defective Microspore Development1 is required for microspore cell integrity and pollen wall formation in rice

: Highly coordinated pollen wall patterning is essential for male reproductive development. Here, we report the identification of Defective Microspore Development1 (DMD1), which encodes a nuclear-localized protein possessing transactivation activity. DMD1 is preferentially expressed in the tapetum and microspores during postmeiotic development. Mutations in DMD1 cause a male sterile phenotype with impaired microspore cell integrity. The mutants display abnormal callose degradation, accompanying with inhibited primexine thickening in the newly released microspores. Several genes associated with callose degradation and primexine formation are down-regulated in dmd1 anthers. In addition, irregular Ubisch body morphology and discontinuous endexine occur, and the baculum is completely absent in dmd1. DMD1 interacts with Tapetum Degeneration Retardation (TDR), a basic helix-loop-helix transcription factor required for exine formation. Taken together, our results suggest that DMD1 is responsible for microspore cell integrity, primexine formation, and exine pattern formation during rice microspore development.