Somatic and Reproductive Cell Development in Rice Anther Is Regulated by a Putative Glutaredoxin

The switch from mitosis to meiosis is one of the most pivotal events in eukaryotes undergoing sexual reproduction. However, the mechanisms orchestrating meiosis initiation remain elusive, particularly in plants. Flowering plants are heterosporous, with male and female spore genesis adopting different developmental courses. We show here that plant pollen mother cells contain a specific meiosis initiation machinery through characterization of a rice (Oryza sativa) gene, MICROSPORELESS1 (MIL1). The mil1 mutant does not produce microspores in anthers but has the normal female fertility. Detailed molecular and cytological investigations demonstrate that mil1 anthers are defective in the meiotic entry of sporogenous cell progenies and in the differentiation of surrounding somatic cell layers, resulting in locules filled with somatic cells instead of microspores. Furthermore, analysis of mil1 msp1 double mutants reveals that due to the absence of MIL1, the cells in their anther locule center do not activate meiotic cell cycle either, generating a similar anther phenotype to mil1. MIL1 encodes a plant-specific CC-type glutaredoxin, which could interact with TGA transcription factors. These results suggest meiotic entry in microsporocytes is directed by an anther-specific mechanism, which requires MIL1 activity, and redox regulation might play important roles in this process.