Effects of Haplotypes of the Rice Sucrose Transporter Genes OsSWEET11 and OsSWEET15 on Grain Traits in Local Yunnan Germplasm Resources

The translocation of sucrose into spike grains during the grain-filling stage directly affects rice yield and quality. The sugar transporters OsSWEET11 and OsSWEET15 are key sucrose transporters essential for rice (Oryza sativa L.) grain filling. To elucidate their effects on grain traits, we analyzed sequence polymorphisms of these two genes in 139 landrace rice varieties from Yunnan, China, and conducted association and haplotype analyses. Our results indicated that grain filling degree was closely associated with grain shape, where wider grains negatively impacted grain plumpness. The association analysis revealed eight significant SNPs: six located in the coding region of OsSWEET15 that influenced grain length, thickness, density, and 1000-grain weight (TGW), while two SNPs in OsSWEET11 affected TGW and the thickness of milled rice grains. Haplotype analysis further validated these trait associations: OsSWEET15 Hap2 and Hap3 conferred longer grains (with Hap2 additionally increasing TGW and Hap3 enhancing grain density/plumpness), whereas Hap1 produced narrower and thicker grains. Consistently, OsSWEET11 Hap2 was also linked to higher TGW. The superior haplotypes identified here deepen our understanding of the genetic basis of rice grain filling and serve as potential molecular markers for marker-assisted rice breeding.