Bioinformatic and functional analyses reveal the expansion base of the rice polyketide synthase III superfamily and the synergistic roles of OsPKS1 and OsPKS2 in male reproduction

Abstract

Type III polyketide synthase (PKS III) superfamily members are involved in plant secondary metabolism, which is important for plant development and resistance to biological and abiotic stress. However, the functions of most PKS III superfamily members in rice (Oryza sativa L.) remain unknown. Here, we identified PKS III genes in rice and performed phylogenetic analysis. This divided the 28 rice PKS III superfamily genes into six subgroups, the chalcone synthase (CHS) group and the CHS-like groups CHSL I–V. These PKS III genes share significant genomic synteny. CHS, CHSL I, and II genes are present in single copies in the rice genome, whereas CHSL III–V are present in gene clusters. The chromosomal regions harboring PKS III genes contain numerous transposable elements, which might underlie the duplication and expansion of the PKS III superfamily. Heatmap analysis indicated that PKS III genes in the same subgroup have similar expression patterns. We knocked out two anther-specific genes (OsPKS1 and OsPKS2) from subgroup CHSL II in rice to investigate their roles in male reproduction. The double knockout mutant ospks1/2 exhibited severer defects in exine and no-pollen phenotype, which is different from the partially abortive-pollen phenotype of the ospks1 and ospks2 single mutants. OsPKS1 is upregulated in ospks2 mutants and OsPKS2 is upregulated in ospks1 mutants, suggesting that the coordinated activities of OsPKS1 and OsPKS2 are essential for pollen development. Our findings provide new clues about the evolution of the PKS III superfamily and reveal the synergistic roles of OsPKS1 and OsPKS2 in regulating male reproduction in rice.