Phytophthora infestans RXLR effector PITG20303 targets a potato MKK1 protein to suppress plant immunity

Abstract

Pathogens secret a plethora of effectors into the host cell to modulate plant immunity. Analysing the role of effectors in altering the function of their host target proteins will reveal critical components of the plant immune system. Here we show that Phytophthora infestans RXLR effector PITG20303, a virulent variant of AVRblb2 (PITG20300) that escapes recognition by the resistance protein Rpi-blb2, suppresses PAMP-triggered immunity (PTI) and promotes pathogen colonization by targeting and stabilizing a potato MAPK cascade protein, StMKK1. Both PITG20300 and PITG20303 target StMKK1, as confirmed by multiple in vivo and in vitro assays, and StMKK1 was shown to be a negative regulator of plant immunity, as determined by overexpression and gene silencing. StMKK1 is a negative regulator of plant PTI, and the kinase activities of StMKK1 are required for its suppression of PTI and effector interaction. PITG20303 depends partially on MKK1, PITG20300 does not depend on MKK1 for suppression of PTI-induced reactive oxygen species burst, while the full virulence activities of nuclear targeted PITG20303 and PITG20300 are dependent on MKK1. Our results show that PITG20303 and PITG20300 target and stabilize the plant MAPK cascade signalling protein StMKK1 to negatively regulate plant PTI response.

The role of the MAP kinase−kinase protein StMKK1 in potato immunity to different pathogens

“…1f–h ). These results indicate that StMKK1 negatively regulates plant immunity to the late-blight disease pathogen P. infestans in potato, similar to our previous findings in N. benthamiana 26 .…”

“…GFP-StMKK1 and StMKK1-pART27-RNAi plasmids were constructed as described previously 24 , 26 . Agrobacterium strain C58C1 carrying GFP-StMKK1 or GFP-GUS plasmids was cultured in liquid LB medium with appropriate antibiotics at 28 °C.…”

Potato StMPK7 is a downstream component of StMKK1 and promotes resistance to the oomycete pathogen Phytophthora infestans

“…Total proteins were extracted using GTEN buffer as described by Du et al (2021). For Co-IP assays, for each 1.6 ml of total protein extraction a 12 µl of GFP-trap_A beads (Chromotek) were added, and the mixtures were incubated for 2 hr with gentle shaking at 4 °C before proteins were spun down.…”

“…The StMEK1-StMPK1/StWIPK (the orthologs of Arabidopsis AtMKK4/5-AtMPK6/3) cascade is reported in potato to participate in immunity to P. infestans (Yamamizo et al, 2006). Our previous work showed that a P. infestans RXLR effector targets and stabilizes the potato negative immune regulator StMKK1 (Du et al, 2021).…”

Erratum

“…Since its publication, the authors of Du et al (2021) have brought to our attention an error in the numbering of the author affiliations in their article. The correct affiliations are shown below.…”