The Arabidopsis lectin receptor kinase LecRK-I.9 enhances resistance to Phytophthora infestans in Solanaceous plants

Phytophthora species are notorious plant pathogens which cause a variety of devastating crop diseases. Phytophthora pathogens secrete a plethora of effector proteins, several of which are known to interact with receptors in the host cell thereby either activating or suppressing defense responses. Unlike animals, plants lack an adaptive immune system; however, they are not defenseless and have acquired other mechanisms to withstand pathogens. Receptor proteins play important roles in sensing alterations at the plant cell wall and in mediating responses upon pathogen attack. This paper focuses on the Arabidopsis lectin receptor kinase LecRK-I.9, a mediator of cell wall – plasma membrane (CW-PM) adhesions that is known to bind in vitro to the Phytophthora infestans effector IPI-O via the cell attachment motif RGD. T-DNA mutants deficient in LecRK-I.9 and transgenic Arabidopsis lines expressing ipiO1 were found to behave as phenocopies. Both show a ‘gain-of-susceptibility’ phenotype towards the Arabidopsis pathogen Phytophthora brassicae and are disturbed in callose deposition. Overall, the results suggest that destabilizing the CW-PM continuum is a strategy for Phytophthora to promote infection. As countermeasure, the host may want to strengthen CW-PM adhesions, and the novel resistance component LecRK-I.9 apparently functions in this process