Perception and First Defense Responses Against Pseudomonas syringae pv. phaseolicola in Phaseolus vulgaris: Identification of Wall-Associated Kinase Receptors

Abstract

Common bean (Phaseolus vulgaris L.) is attacked by several pathogens such as the biotrophic gamma-proteobacterium Pseudomonas syringae pv. phaseolicola (Pph). In order to study the Pph-bean interaction during the first stages of infection, leaf disks of a susceptible bean variety named Riñón were infected with a pathogenic Pph. Using this experimental system, six new putative Wall-Associated Kinase (WAKs) receptors, previously identified in silico, were tested. These six bean WAKs (PvWAKs) showed high protein sequence homology to the well-described Arabidopsis WAK1 (AtWAK1) receptor and, by phylogenetic analysis, clustered together with AtWAKs. The expression of PvWAK1 increased at very early stages after the Pph infection. Time course experiments were performed to evaluate the accumulation of apoplastic H2O2, Ca2+ influx, total H2O2, antioxidant enzymatic activities, lipid peroxidation, and the concentrations of abscisic acid (ABA) and salicylic acid (SA), as well as the expression of six defense-related genes – MEKK-1, MAPKK, WRKY33, RIN4, PR1 and NPR1. The results showed that overexpression of PR1 occurred 2 h after Pph infection without a concomitant increase in SA levels. Although apoplastic H2O2 increased after infection, the oxidative burst was neither intense nor rapid and an efficient antioxidant response did not occur, suggesting that the observed cellular damage was due to the initial increase in total H2O2 at early time points after infection. In conclusion, the Riñón variety can perceive the presence of Pph, but this recognition only results in a modest and slow activation of host defenses, leading to high susceptibility to Pph.

Transcriptomic reprogramming in a susceptiblePhaseolus vulgarisL. variety duringPseudomonas syringaeattack: The key role of homogalacturonan methylation

“…Plant immune-signaling pathways and transcriptional reprogramming have been proved to be activated within the first 12 hours after the apparition of the pathogen (Ngou et al, 2022). Recently, De la Rubia et al (2021a) have demonstrated that the expression of PR1 and other plant defense-related genes increased past 2 hours upon Pph infection in P. vulgaris var. riñón .…”

“…This could be explained by the fact that P. vulgaris var. riñón is susceptible to Pph (Monteagudo et al, 2006; De la Rubia et al, 2021a) and the plant would trigger some early defense responses at 2 hours, which would be successfully stopped by the pathogen effectors at 9 hours post infection, diminishing the plant responses to Pph.…”

“…However, many important crops are susceptible to pathogens, such as the common bean variety riñón used in this study, which is susceptible to Pph (Monteagudo et al, 2006; De la Rubia et al, 2021). Although several advances have been made to reveal the mechanisms behind this lack of resistance (De la Rubia et al, 2021a; De la Rubia et al, 2021b), the study of the changes in gene expression upon Pph infection of common bean leaves would help to understand the infection process. Therefore, we performed a transcriptomic analysis by RNA-seq of infected common bean leaves at 0, 2 and 9 hours post infection, once we collected evidence that the infection was taking place (Figure 1).…”

“…In the case of common bean variety riñón , which is susceptible to the attack of the biotrophic gamma-proteobacteria Pseudomonas syringae pv. phaseolicola (Pph), some of the defensive pathways, as well as some probable points where the pathogen interferes with these pathways, have already been described in De la Rubia et al (2021a and b). It was determined that, shortly after the infection starts, this variety is able to perceive the presence of Pph but it is unable to produce a quick and effective defense response due to the lack of a peak in the production of SA soon after infection (De la Rubia et al, 2021a).…”

“…phaseolicola (Pph), some of the defensive pathways, as well as some probable points where the pathogen interferes with these pathways, have already been described in De la Rubia et al (2021a and b). It was determined that, shortly after the infection starts, this variety is able to perceive the presence of Pph but it is unable to produce a quick and effective defense response due to the lack of a peak in the production of SA soon after infection (De la Rubia et al, 2021a). In addition, the inoculation of Pph modified the pectic components of common bean CWs after 15 days of infection (De la Rubia et al, 2021b).…”