Function characterization of a soybean sucrose transporter GmSUT4.2 involved in plant growth, development, and crop yield

Sucrose transporters (SUTs) play an important role in regulating carbohydrate homogeneity, and well understand of the regulatory control of sugars into demanding sink is important for plant growth and seed yield. Nevertheless, key sucrose transporters that are involved in this process are not identified or characterized in soybean. Here, a sucrose transporter gene, GmSUT4.2, belonging to the SUT4 subfamily was cloned and functionally characterized. It encodes a protein of 513 amino acids which is localized in the plasma membrane. Real-time quantitative PCR showed that the expression of this gene was induced by sucrose and the sucrose transport capability could be functionally recovered by the expression of GmSUT4.2 in a sucrose transport dysfunction mutant yeast SUSY7/ura3. In soybean (Glycine max L.), overexpression of GmSUT4.2 significantly promoted sucrose-stimulated hairy root growth and improved the capacity of sucrose uptake. However, the knockdown of GmSUT4.2 in soybean by CRISPR/Cas9 caused a small leaf phenotype, which could also be observed in the ethyl methane sulfonate (EMS)-induced GmSUT4.2 mutant. In addition, the significantly low level of sucrose and soluble sugars were recorded in these mutants compared with wild-type plants (WT). As a result, the soybean yield and biomass in mutants were decreased by more than ~ 30% compared with WT under greenhouse conditions. While overexpression of GmSUT4.2 (OE) in Arabidopsis showed a pleiotropic phenotype with more rosette leaves and branches, resulting in a higher yield (40.07%) than those of wild types. These results suggest that the GmSUT4.2 played key roles in the regulation of plant growth and development as well as yield formation.