Overexpression of sesame O-acetylserine(thiol)lyase induces male sterility by delaying tapetum programmed cell death

Abstract

Male sterile lines are key resources for hybrid seed production and for ensuring high varietal purity. However, the genes and mechanisms underlying sesame male sterility remain largely unknown. Hence, this study identified an O-acetylserine(thiol)lyase gene SiOASTL1 and functionally characterized its roles in inducing defective anther development. Spatiotemporal expression analysis revealed that SiOASTL1 is significantly (2.7 fold) up-regulated in sterile sesame anthers at the microspore stage compared with fertile ones. Sequence and phylogenetic analyses showed that SiOASTL1 is homologous to Arabidopsis OAS-TL plastid isoforms. We thus overexpressed SiOASTL1 in Arabidopsis to unravel its regulatory roles. Cytological observation revealed that SiOASTL1 overexpression transformed transgenic plants into male sterile lines arising at the microspore development stage. SiOASTL1 overexpression decreased cysteine biosynthesis and down-regulated the expression of the sporopollenin synthesis-related genes, including AtTKPR1, AtTKPR2, AtPKSA, and AtPKSB in transgenic Arabidopsis. Consequently, the tapetum programmed cell death (PCD) was delayed, resulting in the formation of defective pollen grains with irregular walls and empty cytoplasm. Our findings prove that the induction of SiOASTL1 expression disrupts pollen development and contributes to sesame male sterility. Moreover, these results suggest that genetic manipulation of SiOASTL1 expression may facilitate the development of new hybrid varieties in sesame and other crops.