2020 Review on Plant Immunity in Current Opinion in Immunology
2019 Annual Review on Gram-positive plant-associated actinobacterial pathogens.
Surface-localized pattern recognition receptors (PRRs) can perceive molecular features such as MAMPs, damage-associated molecular patterns, and effectors from diverse pathogens. PRR perception induces a variety of responses including the production of antimicrobial reactive oxygen species (ROS), calcium influx, kinase cascades, defense gene expression, and biosynthesis of plant defense hormones such as salicylic acid (SA) and ethylene.
Modified from Lolle, Stevens, and Coaker. 2020. Opinions in Immunology.
In the tomato-Clavibacter michiganensis pathosystem, it is possible for plant immunity to be activated and impact disease; applications of an SA-analog decrease bacterial titer, and microarray analyses show up-regulation of ethylene biosynthesis genes during infection. Since these bacteria lack the molecular protein machinery to inject effectors into the plant cell, it's likely if perception and response will occur on the surface-localized receptors (PRRs) of the plant host.
Plant-associated bacteria possess multiple MAMPs. The well-known MAMPs, csp22 and elf18, are found in Clavibacter genomes with high similarity to canonical epitopes. I am working toward verifying Cm elf18 and csp22 are immunogenic through different immune-related outputs such as the production of reactive oxygen species (ROS), which acts as an antimicrobial agent in the plant host. This work will focus on characterizing the potential for these MAMPs to induce plant immunity and how this plays into the biological context of disease suceptibility.
Genes that encode MAMPs display signatures of overall negative selection with small regions of very high positive selection (the immunogenic region). Multiple novel MAMPs have been discovered in G- pathogens using selection patterns. This method has also predicted hypothesized MAMPs in G+ actinobacteria Rhodococcus. I will carry out a similar approach to predict unique Gram-positve MAMPs.
Since it's unknown whether a native or non-native host would carry a cognate receptor candidate G+ MAMP peptides will be tested for elicitation of an immune response in hosts and nonhosts from diverse plant families. I will measure the production of ROS and ethylene, a plant defense hormone known to be induced in the Cm-tomato pathosystem. This work will provide early evidence for Gram-positive specific elicitation of the plant immune system.