Plant hormones act in a complex network where their pathways regulate and interact to control different mechanisms, such as development and stress responses. This crosstalk between hormones can be exploited by pathogens to suppress plant defense responses and thereby increase pathogen growth. Pseudomonas syringae pathogenicity is reliant on a Type III secretion system (TTSS) that acts as a specialized injection apparatus to deliver virulence proteins, known as type III effectors (TTEs), into the plant cell cytosol. In my work, I have screened hormone inducible promoter::GUS transgenic Arabidopsis thaliana lines against a P. syringae TTE library in order to identify TTEs involved in the perturbation of hormone signaling in planta. Through this screen I identified two P. syringae TTEs, HopAK1 and HopAL1, both belonging to the same bacterial strain P. syringae pv. maculicola ES4326. I found that HopAK1 can sensitize A. thaliana plants to auxin. On the other hand, HopAL1 activates auxin signaling. Monitoring of auxin signaling was done using transgenic DR5::GUS plants. Both TTEs render the plant susceptible to bacterial infection, highlighting a potential relationship between increased auxin signaling and virulence.

Plant hormones act in a complex network where their pathways regulate and interact to control different mechanisms, such as development and stress responses. This crosstalk between hormones can be exploited by pathogens to suppress plant defense responses and thereby increase pathogen growth. Pseudomonas syringae pathogenicity is reliant on a Type III secretion system (TTSS) that acts as a specialized injection apparatus to deliver virulence proteins, known as type III effectors (TTEs), into the plant cell cytosol. In my work, I have screened hormone inducible promoter::GUS transgenic Arabidopsis thaliana lines against a P. syringae TTE library in order to identify TTEs involved in the perturbation of hormone signaling in planta. Through this screen I identified two P. syringae TTEs, HopAK1 and HopAL1, both belonging to the same bacterial strain P. syringae pv. maculicola ES4326. I found that HopAK1 can sensitize A. thaliana plants to auxin. On the other hand, HopAL1 activates auxin signaling. Monitoring of auxin signaling was done using transgenic DR5::GUS plants. Both TTEs render the plant susceptible to bacterial infection, highlighting a potential relationship between increased auxin signaling and virulence.