Arabidopsis Lectin Receptor Kinase P2K2 Is a Second Plant Receptor for Extracellular ATP and Contributes to Innate Immunity.

An Quoc Pham,Cuong The Nguyen,Sung-Hwan Cho,Gary Stacey

doi:10.1104/pp.19.01265

Abstract

In animals, extracellular ATP is a well-studied signaling molecule that is recognized by plasma membrane-localized P2-type purinergic receptors. However, in contrast, much less is known about purinergic signaling in plants. P2 receptors play critical roles in a variety of animal biological processes, including immune system regulation. The first plant purinergic receptor, Arabidopsis (Arabidopsis thaliana) P2K1 (L-type lectin receptor kinase-I.9), was shown to contribute to plant defense against bacterial, oomycete, and fungal pathogens. Here, we demonstrate the isolation of a second purinergic receptor, P2K2, by complementation of an Arabidopsis p2k1 mutant. P2K2 (LecRK-I.5) has 74% amino acid similarity to P2K1. The P2K2 extracellular lectin domain binds to ATP with higher affinity than P2K1 (dissociation constant [K d] = 44.47 ± 15.73 nm). Interestingly, p2k2 and p2k1 p2k2 mutant plants showed increased susceptibility to the pathogen Pseudomonas syringae, with the double mutant showing a stronger phenotype. In vitro and in planta studies demonstrate that P2K2 and P2K1 interact and cross-phosphorylate upon extracellular ATP treatment. Thus, similar to animals, plants possess multiple purinergic receptors.

Highlights

Adenosine 5'-triphosphate (ATP) is well-known as the source of cellular energy in all organisms.Under normal conditions, cells maintain mM levels of intracellular ATP and nM levels of extracellular ATP
We identify P2K2 (LecRK-I.5) as a second Arabidopsis extracellular ATP receptor by screening various AtLecRK clade I RLKs for their ability to complement an Arabidopsis p2k1 mutant
The results suggest that P2K2, in addition to P2K1, is a critical component of ATP signaling through the pathogen response pathway

Summary

Introduction

Adenosine 5'-triphosphate (ATP) is well-known as the source of cellular energy in all organisms. The expression of individual LecRK genes was found to be responsive to specific hormone treatments, abiotic stresses, elicitor treatments, or pathogen infection, suggesting a functional role for these receptors under these specific conditions (Bouwmeester and Govers, 2009). While the specific functions as well as ligands of most LecRK family members remain unknown, there appears to be a general association of these receptors with the plant response to both abiotic and biotic stress. Given that eATP was shown to mediate a variety of plant processes (Tanaka et al, 2010), it seemed reasonable to suggest that plants encode multiple purinergic receptors. We identify P2K2 (LecRK-I.5) as a second Arabidopsis extracellular ATP receptor by screening various AtLecRK clade I RLKs for their ability to complement an Arabidopsis p2k1 mutant. P2K1 or P2K1/P2K2 function are significantly more susceptible to pathogen infection

Results

Discussion

Materials and methods