Sugar Transporter HmSWEET8 Cooperates with HmSTP1 to Enhance Powdery Mildew Susceptibility in Heracleum...

The powdery mildew caused by Eeysiphe heraclei is a serious concern in Heracleum moellendorffii Hance. Therefore, exploring the mechanisms underlying sugar efflux from host cells to the fungus during the plant-fungus interaction showed great significance. The study successfully cloned HmSWEET8 and HmSTP1 genes based on RNA-seq technology. The complementation assays in yeast EBY.VW4000 found HmSWEET8 and HmSTP1 transporting hexose. Over-expressing or silencing HmSWEET8 in H. moellendorffii leaves increased or decreased powdery mildew susceptibility by changing glucose concentration in infective sites. Meanwhile, over-expressing HmSTP1 in H. moellendorffii leaves also increased powdery mildew susceptibility by elevating the glucose content of infective areas. Additionally, HmSTP1 expression was up-regulated obviously in HmSWEET8 over-expressed plants and inhibited significantly in HmSWEET8 silenced plants. Co-expressing HmSWEET8 and HmSTP1 genes significantly increased powdery mildew susceptibility compared with over-expressed HmSWEET8 or HmSTP1 plants alone. The results demonstrated that HmSTP1 may assist with HmSWEET8 to promote E. heraclei infection. Consequently, the infection caused by E. heraclei resulted in the activation of HmSWEET8, leading to an increased transfer of glucose to the apoplasmic spaces at the sites of infection, then, HmSTP1 facilitated the transport of glucose into host cells, promoting powdery mildew infection.