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 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.