The SbTDR gene is required for anther development and male fertility in Sorghum bicolor

Anthers are essential in plant reproduction and are also crucial in agriculture, because hybrid seed production typically relies on the manipulation of male fertility. Sorghum (Sorghum bicolor L. Moench) is the fifth most produced grain crop in the world. However, relatively little is known about the genetic mechanisms that regulate anther development and male fertility in sorghum. Here, we report the morphological characterization of anther development in wild-type sorghum BTx623 and the Sorghum bicolor tapetal degeneration retardation (Sbtdr) mutant, as well as identification of the causal gene SbTDR. Our results showed that the Sbtdr mutant formed small, white anthers that failed to produce pollen grains. We classified sorghum anther development into 13 main stages based on major cellular landmarks observed in semi-thin sections of anthers. Our analysis demonstrated that the Sbtdr mutant is defective in tapetal cell degeneration. Moreover, in situ hybridization revealed that the SbTDR gene, which encodes a bHLH transcription factor, is primarily expressed in tapetal cells at the microspore stage. Our discoveries highlight the importance of the SbTDR bHLH transcription factor in controlling tapetal cell differentiation and male sterility, which may help develop novel hybrid breeding systems in sorghum.