Phloem-Specific Overexpression of the Sucrose Transporter, AtSUC2, and Robust Plant Growth

Sucrose is the primary carrier of assimilated carbon from photosynthesis in higher plants. Owing to the dual function of sucrose as the primary carbon source and a signaling molecule, sucrose allocation is crucial for optimal plant growth and development throughout the entire life cycle. Genetic evidence shows that the Arabidopsis sucrose transporter, AtSUC2, plays a predominant role in loading sucrose into the phloem, a crucial step for sucrose export from mature (source) leaves. In this process, no other sucrose transporters in Arabidopsis have redundant functions to AtSUC2. We have identified and characterized an Arabidopsis T-DNA insertion mutant, suc2-oe, with SUC2 overexpression in a phloem-specific pattern. suc2-oe plants display a striking growth phenotype with a larger rosette at bolting, higher seed yield, and higher biomass than the wild-type plants. Furthermore, we recapitulated the growth phenotype by re-constructing the suc2-oe allele and introducing it into a suc2 null-mutant line. Taken together, our data provide convincing evidence that phloem-specific SUC2 overexpression is necessary and sufficient for enhancing plant growth at both vegetative and reproductive stages.