Novel molecular components involved in callose-mediated Arabidopsis defense against Salmonella enterica and Escherichia coli O157:H7

Abstract

Background: Food contamination with Salmonella enterica and enterohemorrhagic Escherichia coli is among the leading causes of foodborne illnesses worldwide and crop plants are associated with > 50% of the disease outbreaks. However, the mechanisms underlying the interaction of these human pathogens with plants remain elusive. In this study, we have explored plant resistance mechanisms against these enterobacteria and the plant pathogen Pseudomonas syringae pv. tomato (Pst) DC3118, as an opportunity to improve food safety. Results: We found that S. enterica serovar Typhimurium (STm) transcriptionally modulates stress responses in Arabidopsis leaves, including induction of two hallmark processes of plant defense: ROS burst and cell wall modifications. Analyses of plants with a mutation in the potentially STm-induced gene EXO70H4 revealed that its encoded protein is required for stomatal defense against STm and E. coli O157:H7, but not against Pst DC3118. In the apoplast however, EXO70H4 is required for defense against STm and Pst DC3118, but not against E. coli O157: H7. Moreover, EXO70H4 is required for callose deposition, but had no function in ROS burst, triggered by all three bacteria. The salicylic acid (SA) signaling and biosynthesis proteins NPR1 and ICS1, respectively, were involved in stomatal and apoplastic defense, as well as callose deposition, against human and plant pathogens. Conclusions: The results show that EXO70H4 is involved in stomatal and apoplastic defenses in Arabidopsis and suggest that EXO70H4-mediated defense play a distinct role in guard cells and leaf mesophyll cells in a bacteriadependent manner. Nonetheless, EXO70H4 contributes to callose deposition in response to both human and plant pathogens. NPR1 and ICS1, two proteins involved in the SA signaling pathway, are important to inhibit leaf internalization and apoplastic persistence of enterobacteria and proliferation of phytopathogens. These findings highlight the existence of unique and shared plant genetic components to fight off diverse bacterial pathogens providing specific targets for the prevention of foodborne diseases.

A Simple Assay to Assess Salmonella enterica Persistence in Lettuce Leaves After Low Inoculation Dose

“…Although S. enterica induces plant defense responses ( Meng et al, 2013 ; Garcia and Hirt, 2014 ; Melotto et al, 2014 ; Oblessuc et al, 2020 ), it can still persist for long periods in the leaf apoplast depending on the bacterial strain and the plant genotype ( Wong et al, 2019 ; Jacob and Melotto, 2020 ). Furthermore, recent studies have shown that variations in the S. enterica culturing conditions, such as temperature and nutrients in the medium ( Kroupitski et al, 2019 ), and environmental conditions for the plant cultivation, such as temperature and humidity ( Deblais et al, 2019 ; Jechalke et al, 2019 ; Roy and Melotto, 2019 ), can interfere mainly with the ability of S. enterica to internalize plant tissues.…”

“…Salmonella enterica is one of the most common human pathogens found in fresh produce ( Bennett et al, 2018 ; Melotto et al, 2020 ). Previously, plants were thought to be passive vectors for human pathogens, but recent studies showed that S. enterica can induce plant defense responses ( Meng et al, 2013 ; Garcia and Hirt, 2014 ; Melotto et al, 2014 ; Oblessuc et al, 2020 ). Intriguingly, although the mechanism is not fully understood, this bacterium can overcome plant defense ( Roy et al, 2013 ; Wahlig et al, 2019 ) and survive for weeks inside diverse plants species, including lettuce ( Lactuca sativa L.) ( Islam et al, 2004 ; Kroupitski et al, 2009 , 2011 ; Jechalke et al, 2019 ; Roy and Melotto, 2019 ).…”

Impairment of the Zn/Cd detoxification systems affects the ability of Salmonella to colonize Arabidopsis thaliana

“…The advantage of competition assays, which have been already used in animal infection studies, is that of minimizing effects due to uncontrolled experimental variability and thus directly comparing the fitness of two different strains in the same niche at the same time. This could be particularly useful in inoculation experiments of plants, where both Salmonella growth conditions and plant status have shown to greatly influence the outcome of the infection ( Kroupitski et al, 2009 ; Oblessuc et al, 2020 ).…”

Pseudomonas phaseolicola preferentially modulates genes encoding leucine-rich repeat and malectin domains in the bean landrace G2333

“…The number of reads assigned to each gene was determined and read counts were normalized with the log 2 counts per million (CPM) normalization method (Law et al 2016). Similar to a previously described analysis (Oblessuc et al 2020 ), the log 2 fold change (FC) value for each gene was calculated with its normalized expression in Pph - versus mock-inoculated samples, and DEG were called based on the Z-ratio method (Cheadle et al 2003 ). The Z-ratio approach determines which genes have significantly higher FC than other genes in the data set.…”