OsMAPK6 Affects Male Fertility by Reducing Microspore Number and Delaying Tapetum Degradation in Oryza sativa L.

The mitogen-activated protein kinase(MAPK)cascade is important in stress signal transduction and plant development.In the present study,we identified a rice(Oryza sativa L.)mutant with reduced fertility,Oryza sativa mitogen-activated protein kinase 6(osmapk6),which harbored a mutated MAPK gene.Scanning and transmission electron microscopy,quantitative RT-PCR analysis,TUNEL assays,RNA in situ hybridization,longitudinal and transverse histological sectioning,and map-based cloning were performed to characterize the osmapk6 mutant.The gene OsMAPK6 was expressed throughout the plant but predominantly in the microspore mother cells,tapetal cells,and microspores in the anther sac.Compared with the wild type,the total number of microspores was reduced in the osmapk6 mutant.The formation of microspore mother cells was reduced in the osmapk6 anther sac at an early stage of anther development,which was the primary reason for the decrease in the total number of microspores.Programmed cell death of some tapetal cells was delayed in osmapk6 anthers and affected exine formation in neighboring microspores.These results suggest that OsMAPK6 plays pivotal roles in microspore mother cell formation and tapetal cell degradation.

UDP-glucose epimerase 1,moonlighting as a transcriptional activator,is essential for tapetum degradation and male fertility in rice

Multiple enzymes perform moonlighting functions distinct from their main roles.UDP-glucose epimerases(UGEs),a subclass of isomerases,catalyze the interconversion of UDP-glucose(UDP-Glc)and UDP-galactose(UDP-Gal).We identified a rice male-sterile mutant,osuge1,with delayed tapetum degradation and abortive pollen.The mutant osuge1 protein lacked UDP-glucose epimerase activity,resulting in higher UDP-Gal content and lower UDP-Glc levels in the osuge1 mutant compared with the wild type.Interestingly,we discovered that OsUGE1 participates in the TIP2/bHLH142–TDR–EAT1/DTD transcriptional regulatory cascade involved in tapetum degradation,in which TIP2 and TDR regulate the expression of OsUGE1 while OsUGE1 regulates the expression of EAT1.In addition,we found that OsUGE1 regulates the expression of its own gene by directly binding to an E-box element in the OsUGE1 promoter.Collectively,our results indicate that OsUGE1 not only functions as a UDP-glucose epimerase but also moonlights as a transcriptional activator to promote tapetum degradation,revealing a novel regulatory mechanism of rice reproductive development.