The lectin receptor kinase LecRK-I.9 is a novel Phytophthora resistance component and a potential host target for a RXLR effector

In plants,an active defense against biotrophic pathogens is dependent on a functional continuum between the cell wall (cw) and the plasma membrane (pm). it is thus anticipated that proteins maintaining this continuum also function in defense. the legume-like lectin receptor kinase lecrk-i.9 is a putative mediator of cw-pm adhesions in arabidopsis and is known to bind in vitro to the phytophthora infestans rxlr-deer effector ipi-o via a rgd cell attachment motif present in ipi-o. here we show that lecrk-i.9 is associated with the plasma membrane,and that two t-dna insertions lines deficient in lecrk-i.9 (lecrk-i.9) have a 'gain-of-susceptibility' phenotype specifically towards the oomycete phytophthora brassicae. accordingly,overexpression of lecrk-i.9 leads to enhanced resistance to p. brassicae. a similar 'gain-of-susceptibility' phenotype was observed in transgenic arabidopsis lines expressing ipio (35s-ipio1). this phenocopy behavior was also observed with respect to other defense-related functions; lecrk-i.9 and 35s-ipio1 were both disturbed in pathogen- and mamp-triggered callose deposition. by site-directed mutagenesis,we demonstrated that the rgd cell attachment motif in ipi-o is not only essential for disrupting the cw-pm adhesions,but also for disease suppression. these results suggest that destabilizing the cw-pm continuum is one of the tactics used by phytophthora to promote infection. as countermeasure the host may want to strengthen cw-pm adhesions and the novel phytophthora resistance component lecrk-i.9 seems to function in this process. © 2011 bouwmeester et al.