The Root Knot Nematode Meloidogyne graminicola Regulates Rice Potassium Uptake by Targeting OsHAK17 to Facilitate Parasitism in Rice

Potassium is an essential element for plant growth and development, and also plays a pivotal role in plant immunity against nematodes. However, it is not clear how plant nematodes manipulate host K+ signalling pathways to disrupt host immunity and promote their parasitism. Here, we demonstrate the rice K+ transporter OsHAK17 was targeted by the effector protein MgCOL from Meloidogyne graminicola nematodes. Genetic and phenotypic analyses revealed that knockout of OsHAK17 in rice resulted in decreased resistance to M. graminicola, while overexpression of OsHAK17 in rice enhanced resistance to M. graminicola. The yeast two-hybrid assay showed OsHAK17 interacted with MgCOL. In situ hybridisation assay showed MgCOL mRNA accumulating in the subventral oesophageal gland of J2 nematodes, while immunolocalisation analysis revealed MgCOL localises to the giant cells during M. graminicola parasitism. Host-induced gene silencing of MgCOL reduced the infection ability of M. graminicola, and over-expressing MgCOL enhanced rice susceptibility to M. graminicola. More importantly, MgCOL-overexpression rice showed decreased K+ accumulation in roots, which was consistent with it in nematode-infected rice. In conclusion, when M. graminicola nematodes infect rice and secrete MgCOL into rice, MgCOL interacts with OsHAK17, resulting in the change of K+ uptake and transportation in rice to enhance susceptibility.