The Emerging Role of PP2C Phosphatases in Tomato Immunity

Abstract

The antagonistic effect of plant immunity on growth likely drove evolution of molecular mechanisms that prevent accidental initiation and prolonged activation of plant immune responses. Signaling networks of pattern-triggered immunity (PTI) and effector-triggered immunity (ETI), the two main layers of plant immunity, are tightly regulated by the activity of protein phosphatases that dephosphorylate their protein substrates and reverse the action of protein kinases. Members of the PP2C class of protein phosphatases have emerged as key negative regulators of plant immunity, primarily from research in the model plant Arabidopsis thaliana, revealing the potential of employing PP2C proteins to enhance plant disease resistance. As a first step towards focusing on the PP2C family for both basic and translational research, we analyzed the tomato genome sequence to ascertain the complement of the tomato PP2C family, identify conserved protein domains and signals in PP2C amino acid sequences, and examine domain combinations in individual proteins. We then identified tomato PP2Cs that are candidate regulators of single or multiple layers of the immune signaling network by in depth analysis of publicly-available RNA-seq datasets. These included expression profiles of plants treated with fungal or bacterial PAMPs, with pathogenic, non-pathogenic and disarmed bacteria, as well as pathogenic fungi and oomycetes. Finally, we discuss the possible use of immunity-associated PP2Cs to better understand the signaling networks of plant immunity and to engineer durable and broad disease resistance in crop plants.

Related PP2C phosphatases Pic3 and Pic12 negatively regulate immunity in tomato toPseudomonas syringae

“…To assess the role of Pic phosphatases in the tomato defense response, we first generated gene-specific guide RNAs (gRNAs) and used CRISPR/Cas9 technology to induce loss-of-function mutations in a set of eight previously identified PP2C-encoding genes and, in two cases ( Pic7 and Pic10 ), an additional two closely-related genes (Sobol et al, 2022) ( Figure 1A and Supplemental Figure S1 ). Agrobacterium-mediated stable transformation with the 10 gRNA constructs was performed using tomato cultivar Rio-Grande PtoR (RG-PtoR, wildtype), which expresses the Pto/Prf genes and recognizes race 0 Pseudomonas syringae pv.…”

“…Pic3 phosphatase activity and its palmitoylation motif are required for its negative regulation of the tomato immune response Pic3 belongs to a large sub-group (over 50 members) of tomato PP2C phosphatases that contain a single conserved PP2C catalytic domain but lack well-known regulatory domains at their N-and C-terminus (Sobol et al, 2022). The catalytic domain contains conserved aspartic acid residues that play a role in binding metal ions such as Mn 2+/ Mg 2+ and substitutions at these residues are known to block metal binding and abolish PP2C phosphatase activity (Couto et al, 2016;Giska and Martin, 2019).…”

“…The PPP and PP2C family members are serine/threonine protein phosphatases that dephosphorylate phospho-serine and -threonine but the sequences of PP2Cs are distinct from those of PPP members (Uhrig et al, 2013). Significant attention has been given to PP2Cs in recent years as many of them are found to regulate biotic and abiotic stresses (Schweighofer et al, 2004; Sobol et al, 2022). In Arabidopsis, several PP2C phosphatases have been implicated in dampening immunity by dephosphorylating defense signaling components.…”

TreeViewer: Flexible, modular software to visualise and manipulate phylogenetic trees

“…TreeViewer have been included in recent publications (Anderegg et al, 2022;Beach et al, 2022;Iwata et al, 2023;Klau et al, 2022;Moreira et al, 2022;Naafs et al, 2021;Sánchez-Baracaldo et al, 2022;Sasoni et al, 2022;Sobol et al, 2022;Wu & Guo, 2022).…”

“…These are available in the online documentation (Bianchini, 2021b) and describe a large variety of different plots, some of which are shown in Figure 1. Plots created using TreeViewer have been included in recent publications (Anderegg et al., 2022; Beach et al., 2022; Gyimesi & Hediger, 2022; Iwata et al., 2023; Klau et al., 2022; Moreira et al., 2022; Naafs et al., 2021; Sánchez‐Baracaldo et al., 2022; Sasoni et al., 2022; Sobol et al., 2022; Visagie et al., 2023; Visagie & Yilmaz, 2023; Wu & Guo, 2022).…”