Soybean GmSUT1 transporter participates in sucrose transport to nodules during rhizobial symbiosis

Symbiotic N 2 fixation depends on a steady supply of carbohydrate to nodules. Sucrose is the main carbohydrate translocated through the phloem to nodules. Some putative sucrose transporter genes have been found in legumes and are highly expressed in nodules. However, none of these are crucial for sucrose transport to nodules. In this study, we characterized a soybean sucrose transporter, GmSUT1 , which was highly expressed in nodules and mainly localized in peripheral fixation zone and vascular bundles of nodules. Soybean transgenic composite plants overexpressing GmSUT1 exhibited increased nodule number and dry weight, and improved plant dry weight and N content compared to control plants when inoculated with rhizobia. Furthermore, the inoculated RNAi plants impaired sucrose transport and showed increased shoot sucrose concentration. In nodules, overexpression of GmSUT1 decreased the sucrose concentration and increased hextose concentrations, whereas RNAi plants decreased glucose concentration compared with the control plants. These results in combination with the subcellular localization of GmSUT1 at the plasma membrane indicate that GmSUT1 plays a role in sucrose transport to nodules to promote soybean nodulation.