Identification of no pollen 1 provides a candidate gene for heterosis utilization in foxtail millet (Setaria italica L.)

Male sterility is a common biological phenomenon in plant kingdom and has been used to generate male-sterile lines, which are important genetic resources for commercial hybrid seed production. Although increasing numbers of male-sterility genes have been identified in rice (Oryza sativa) and Arabidopsis (Arabidopsis thaliana), few male-sterility-related genes have been characterized in foxtail millet (Setaria italica). In this study, we isolated a male-sterile ethyl methanesulfonate-generated mutant in foxtail millet, no pollen 1 (sinp1), which displayed abnormal Ubisch bodies, defective pollen exine and complete male sterility. Using bulk segregation analysis, we cloned SiNP1 and confirmed its function with CRISPR/Cas9 genome editing. SiNP1 encoded a putative glucose-methanol-choline oxidoreductase. Subcellular localization showed that the SiNP1 protein was preferentially localized to the endoplasmic reticulum and was predominantly expressed in panicle. Transcriptome analysis revealed that many genes were differentially expressed in the sinp1 mutant, some of which encoded proteins putatively involved in carbohydrate metabolism, fatty acid biosynthesis, and lipid transport and metabolism, which were closely associated with pollen wall development. Metabolome analysis revealed the disturbance of flavonoids metabolism and fatty acid biosynthesis in the mutant. In conclusion, identification of SiNP1 provides a candidate male-sterility gene for heterosis utilization in foxtail millet and gives further insight into the mechanism of pollen reproduction in plants.