Essential for male fertility, especially for microspore and pollen grain production (PubMed:9750346, Ref.2). Involved in the regulation of cell division after male meiosis I and II to facilitate exit from meiosis and transition to G1 (PubMed:9451956, PubMed:21119056). Expressed at low levels mostly in floral organs during meiosis. Also barely detectable in leaves, stems and roots. Specifically localized within meiotic cells in the anther locules, transiently, only during late meiosis. Sterile plants with abnormal formation of polyads during microsporogenesis, tetrads with more than four pools of chromosomes, after male meiosis, due to an unusual and abnormal cell division without further DNA or chromosome replication after meiosis I and II, and leading to collapsed pollen in flattened anthers (PubMed:9750346, Ref.2). Chromatin recondensation and stretching after meiosis II characterized by a dense microtubule network connecting haploid nuclei in the tetrad stage rearranged into four bipolar spindles as chromatids recondense, as if haploid nuclei entered a third meiotic division (PubMed:9451956, PubMed:21119056). Belongs to the MS5 protein family.