UDP-glucose pyrophosphorylase2 (OsUgp2), a pollen-preferential gene in rice, plays a critical role in starch accumulation during pollen maturation

UDP-glucose pyrophosphorylase (UGPase) is predominantly present and plays significant role in carbohydrate metabolism in plants. Two homologous UGPase genes, OsUgp1 and OsUgp2, exist in rice genome. OsUgp1 has recently been reported to be essential for callose deposition during pollen mother cell and meiosis stages as well as for seed carbohydrate metabolism. In this study, a full-length cDNA of OsUgp2 was isolated from rice anther. Northern blot and RNA in situ hybridization indicated that the expression of OsUgp2 was preferentially in pollen and developmentally regulated. No transcripts were found in leaf, stem, lemma/palea, ripening grain and florets before the uninucleate microspore developmental stage, but a large quantity of OsUgp2 mRNA was found in pollen at the binucleate and mature stages. The immunolocalization of OsUgp2 showed a similar expression pattern to that by RNA in situ hybridization. The function of OsUgp2 was investigated by dsRNA-mediated transcriptional gene silencing. The pollen fertility of 16 independent transgenic rice plants was found between 25% and 90%, which was correlated with the amount of OsUgp2 mRNA. The results of morphological changes and starch variation during pollen development in transgenic rice showed that the abnormal feature of pollen development appeared after the uninucleate microspore stage. Starch failed to accumulate in pollen and thus led to sterile pollens. These results demonstrated that OsUgp2 is a pollen-preferential late gene and plays a key role during pollen maturation, especially for starch accumulation. OsUgp2 complements OsUgp1 to fulfill the UGPase's functions necessary for the full process of pollen development.