Spatiotemporal Production of Reactive Oxygen Species by NADPH Oxidase Is Critical for Tapetal Programmed Cell Death and Pollen Development in Arabidopsis.

Male sterility in angiosperms has wide applications in agriculture, particularly in hybrid crop breeding and gene flow control. Microspores develop adjacent to the tapetum, a layer of cells that provides nutrients for pollen development and materials for pollen wall formation. Proper pollen development requires programmed cell death (PCD) of the tapetum, which requires transcriptional cascades and proteolytic enzymes. Reactive oxygen species (ROS) also affect tapetal PCD, and failures in ROS scavenging cause male sterility. However, many aspects of tapetal PCD remain unclear, including what sources generate ROS, whether ROS production has a temporal pattern, and how the ROS-producing system interacts with the tapetal transcriptional network. We report here that stage-specific expression of NADPH oxidases in the Arabidopsis thaliana tapetum contributes to a temporal peak of ROS production. Genetic interference with the temporal ROS pattern, by manipulating RESPIRATORY-BURST OXIDASE HOMOLOG (RBOH) genes, affected the timing of tapetal PCD and resulted in aborted male gametophytes. We further show that the tapetal transcriptional network regulates RBOH expression, indicating that the temporal pattern of ROS production intimately connects to other signaling pathways regulated by the tapetal transcriptional network to ensure the proper timing of tapetal PCD.