Rice GLUCAN SYNTHASE-LIKE5 promotes Callose deposition in Anthers to maintain proper Male Meiosis Initiation and Progression

Callose is a plant cell-wall polysaccharide whose deposition is spatiotemporally regulated in various developmental processes and environmental stress responses. Appearance of callose in premeiotic anthers is a prominent histological hallmark for the onset of meiosis in flowering plants, whose biological role in meiosis is unknown till date. Here we show that rice GLUCAN SYNTHASE LIKE5 (OsGSL5), a callose synthase, localizes on the plasma membrane of pollen mother cells (PMCs), and is responsible for biogenesis of callose in anther locules through premeiotic and meiotic stages. In osgsl5 mutant anthers mostly lacking callose deposition, aberrant PMCs accompanied by aggregated, unpaired or multivalent chromosomes were frequently observed, and furthermore, a considerable number of mutant PMCs untimely progress into meiosis compared to wild type PMCs. Immunostaining of meiosis-specific protein PAIR2 in premeiotic PMCs revealed precocious meiosis entry in osgsl5 anthers. The findings of this study bestows new knowledge on function of callose in controlling timing of male meiosis initiation and progression, in addition to roles in microsporogenesis, in flowering plants.