The Arabidopsis AtMYB103 gene is required for anther development,but whether the homologous gene in rice has the same role is unclear.Sequence analysis indicated that the rice OsMYB103 gene shares a high sequence similarity with AtMYB103.Therefore,we investigated the functional role of OsMYB103 in anther development using an RNAi approach.The OsMYB103 RNA transcript was expressed most abundantly in flowers,specifically in the tapetum,premeiotic pollen mother cells,and meiotic PMCs.OsMYB103-RNAi transgenic lines grew normally during their vegetative phase but displayed reduced male fertility,a phenotype that was associated with downregulated OsMYB103 transcript levels.Expression of OsMS2,an ortholog of the Arabidopsis AtMS2 gene,was also dramatically reduced in the transgenic plants.Knockdown of OsMYB103 led to defects in tapetum development,and most of the microspores in mature anthers lacked exines.Moreover,OsMYB103 could partially rescue the male sterility phenotype of an AtMYB103 knockout mutant ms188.Taken together,these results indicate that OsMYB103 does have an important role in rice tapetum and microspore development.
ZHANG Sen FANG ZiJun ZHU Jun GAO JuFang YANG ZhongNan
Microsporogenesis in flowering plants plays important roles in sexual reproduction. It has been reported that DEFECTIVE IN EXINE FORMATION1 (DEX1) is essential for exine pattern formation in Arabidopsis thaliana. However, the functions of DEX1 in regulating microspore development are largely not understood. In this study, we show that DEX1 is strongly expressed in the tapetum by using RNA in situ hybridization. dex1 microspores were degenerated and aborted after release from the tetrads. The callose wall in tetrads was thinner in the dex1 mutant than in the wild type, suggesting that DEX1 affects callose formation at the tetrad stage during anther development. RT-PCR and real-time PCR analyses showed that CalS5, which plays an important role in callose synthesis during microspore development, was greatly down-regulated in dex1 plants. DEX1 encodes a membrane protein with one transmembrane domain, one intracellular domain and one extracellular domain. Collectively, our results demonstrate that DEX1 is essential for microspore development, possibly by regulating the expression of CalS5.
