OsPKS1 is required for sexine layer formation, which shows functional conservation between rice and Arabidopsis

The sporopollenin precursors, as a general constituent of sexine, are synthesized in the tapetum and deposited on the pollen surface after transportation and processing. The polyketide synthase condenses the acyl-CoA into a hydroxyalkyl alpha-pyrone, which is predicted to be a component of the sporopollenin precursors. In this study, we found that the rice POLYKETIDE SYNTHASE 1 (OsPKS1) was the orthologue of Arabidopsis POLYKETIDE SYNTHASE A/LESS ADHESIVE POLLEN 6 (PKSA/LAP6) through sequence alignment. The OsPKS1 knockout mutants obtained by Crispr-Cas9-mediated editing exhibited a complete male sterile phenotype. Cytological observations revealed that abnormal bacula deposition and ubisch body structures for sexine formation led to pollen rupture in ospks1. The expression analysis showed that the OsPKS1 was highly expressed in tapetal cells and anther locules from stage 9 to stage 11 during anther development in rice. Subcellular localization demonstrated that the OsPKS1 protein was preferentially localized to the ER. The genomic sequence of OsPKS1 driven by the PKSA/LAP6 promoter restored the sexine pattern of Arabidopsis pksa/lap6. These results indicated that OsPKS1 is required for sexine layer formation in rice and functionally conserved in the sporopollenin synthesis pathway.