tThe molecular function of an isoform of sucrose phosphate synthase (SPS) in rice, OsSPS1, was investigatedusing gene-disruption mutant lines generated by retrotransposon insertion. The progeny of the heterozy-gote of disrupted OsSPS1 (SPS1+/−) segregated into SPS1+/+, SPS1+/−, and SPS1−/−at a ratio of 1:1:0. Thisdistorted segregation ratio, together with the expression of OsSPS1 in the developing pollen revealedby quantitative RT-PCR analysis and promoter–beta-glucuronidase (GUS) fusion assay, suggested thatthe disruption of OsSPS1 results in sterile pollen. This hypothesis was reinforced by reciprocal crosses ofSPS1+/−plants with wild-type plants in which the disrupted OsSPS1 was not paternally transmitted to theprogeny. While the pollen grains of SPS+/−plants normally accumulated starch during their development,pollen germination on the artificial media was reduced to half of that observed in the wild-type control.Overall, our data suggests that sucrose synthesis via OsSPS1 is essential in pollen germination in rice.