Affiliation:
1. Root Biology Center, State Key Laboratory for Conservation and Utilisation of Subtropical Agro‐bioresources South China Agricultural University Guangzhou China
2. College of Resources and Environment Zhongkai University of Agriculture and Engineering Guangzhou China
3. Root Biology Center Fujian Agriculture and Forestry University Fuzhou China
Abstract
AbstractIn arbuscular mycorrhizal (AM) symbiosis, sugars in root cortical cells could be exported as glucose or sucrose into peri‐arbuscular space for use by AM fungi. However, no sugar transporter has been identified to be involved in sucrose export. An AM‐inducible SWEET transporter, GmSWEET6, was functionally characterised in soybean, and its role in AM symbiosis was investigated via transgenic plants. The expression of GmSWEET6 was enhanced by inoculation with the cooperative fungal strain in both leaves and roots. Heterologous expression in a yeast mutant showed that GmSWEET6 mainly transported sucrose. Transgenic plants overexpressing GmSWEET6 increased sucrose concentration in root exudates. Overexpression or knockdown of GmSWEET6 decreased plant dry weight, P content, and sugar concentrations in non‐mycorrhizal plants, which were partly recovered in mycorrhizal plants. Intriguingly, overexpression of GmSWEET6 increased root P content and decreased the percentage of degraded arbuscules, while knockdown of GmSWEET6 increased root sugar concentrations in RNAi2 plants and the percentage of degraded arbuscules in RNAi1 plants compared with wild‐type plants when inoculated with AM fungi. These results in combination with subcellular localisation of GmSWEET6 to peri‐arbuscular membranes strongly suggest that GmSWEET6 is required for AM symbiosis by mediating sucrose efflux towards fungi.