Cytological Analysis and Fine Mapping of paa1 (Post-meiosis Abnormal Anther 1) Mutant with Abnormal Tapetum and Microspore Development.

To further understand the molecular mechanism for rice male reproduction, a rice male sterile mutant paa1 was screened from the rice mutant library generated by treatment with 60 Coγ-rays. Genetic analysis revealed that paa1 is controlled by a single- recessive nuclear gene, and the anthers of the paa1 mutant were smaller than those of WT plants with a white color. Histological analysis demonstrated that the anthers of the paa1 mutant began to turn abnormal at the microspore stage after meiosis, with abnormal degradation of tapetum, deformed Ubisch bodies, and defective pollen exine. TUNEL assay results also confirmed the delay of tapetum PCD in paa1. Map-based cloning was performed for the PAA1 location. As a result, PAA1 was located in a 88-kb region at the end of chromosome 10, which comprises a total of seven candidate genes, and no genes related to anther development have been reported in this region. The results indicate that PAA1 is an essential gene in regulating tapetum development and pollen/microspore formation after rice meiosis.