The functional analysis of OsTDF1 reveals a conserved genetic pathway for tapetal development between rice and Arabidopsis

During anther development, the tapetum provides materials and nutrients for pollen development. In Arabidopsis, several transcription factors have been identified to form a genetic pathway (DYT1-TDF1-AMS-MS188-MS1) for tapetal development and function. DEFECTIVE in TAPETAL DEVELOPMENT and FUNCTION1 (TDF1) is a member of the R2R3 MYB family and is essential for early tapetum development in Arabidopsis. Here, we characterized an ortholog of Arabidopsis TDF1 in rice, OsTDF1 (LOC_Os03g18480). OsTDF1 shares 69 % amino acid sequence identity with AtTDF1 in the putative MYB domain near the N-terminal region. RT-PCR and in situ hybridization show that OsTDF1 is specifically expressed in tapetal cells of rice anthers. The expression of OsTDF1 in Arabidopsis tdf1 mutant restores its fertility, suggesting that this homolog can fulfill the normal function of TDF1 in Arabidopsis. The ostdf1 knockout mutant exhibits a male-sterile phenotype. Its tapetal cells exhibit a vacuolated and hypertrophic phenotype similar to that of Arabidopsis tdf1 mutants. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assays revealed OsTDF1 acts as an essential regulator for tapetum programmed cell death. The qRT-PCR analysis revealed that OsTDF1 acts downstream of UDT1 and upstream of TDR, EAT1, OsMYB103 and PTC1 in rice, suggesting that the genetic pathway for tapetum development is generally conserved between rice and Arabidopsis.