Callose Deficiency Modulates Plasmodesmata frequency and the intercellular space In Rice Anthers

Abstract

Fertilization relies on pollen mother cells able to transit from mitosis-to-meiosis to supply gametes. This process involves remarkable changes at the molecular, cellular and physiological levels including (but not limited to) remodelling of cell wall. During meiosis onset, cellulose content at the pollen mother cell walls gradually declines with the concurrent deposition of the polysaccharide callose in anther locules. We aim to understand the biological significance of cellulose-to-callose turnover in pollen mother cells walls using electron microscopic analyses of rice flowers. Our observations indicate that in wild type anthers, the mitosis-to-meiosis transition coincides with a gradual reduction in the number of cytoplasmic connections called plasmodesmata. A mutant in the Oryza sativa callose synthase GSL5, impaired in callose accumulation in premeiotic and meiotic anthers, displayed a reduction in plasmodesmata frequency among pollen mother cells and tapetal cells suggesting a role for callose in plasmodesmata maintenance. In addition, a significant increase in cell-cell distance between pollen mother cells and impaired premeiotic cell shaping was observed in the mutant. The results suggest that cellulose-to-callose turnover during mitosis-meiosis transition is necessary to maintain cell-to-cell connections and optimal intercellular spacing among anther locular cells explaining the regulatory influence of callose metabolism during meiosis in flowering plants. HighlightsO_LICellulose-to-callose switch during meiosis onset in pollen mother cell walls correlates with changes in cytoplasmic connections called plasmodesmata, among meiocytes and between meiocytes and surrounding somatic cells. C_LIO_LIA mutant in GSL5 (glucan synthase like 5) affects callose deposition but no other cell wall component (e.g., cellulose) in premeiotic and meiotic anthers, except at dyad stage. C_LIO_LIImpaired callose synthesis is proposed to alter plasmodesmata frequency, the extracellular spacing and the shaping of pollen mother cells during mitosis-to-meiosis transition. C_LIO_LIIncrease in plasmodesmata frequency negatively correlates with cell-cell distance between pollen mother cells in both wildtype and a callose mutant. C_LI