Characterization of two type three effectors from Pseudomonas syringae pv. tomato DC3000

Type three secretion system is a unique secretion system that allow bacteria to secrete effector proteins directly into the plant cell. Its presence often defines the ability of the bacteria to elicit disease on susceptible plants and to induce hypersensitive response on resistant plant. Genetic and biochemical studies combined with the sequencing of different bacterial genomes will allow us to begin to identify the complete array of type three effectors. Understanding the role of each of them is the next challenge to appreciate how bacterium promote disease and, ultimately, to provide better disease management.; In Pseudomonas syringae pv. tomato DC3000, the type three secretion system injects more than 40 effectors into the plant cell. Those effectors act collectively to promote parasitism, but the role and function of single effector is still poorly understood. Here, we describe the characterization of two type three effectors from Pseudomonas syringae pv. tomato DC3000 : HopF2 and HopQ1-1. HopF2 is homologous to AvrPphF, a type three effector from Pseudomonas syrinage pv. phaseolicola that induces a resistant reaction on bean plants carrying R1 resistance gene. Moreover, HopF2 has been proposed to start with an unusual ATA instead of ATG and carries a myristoylation site. Here, we reported that HopF2 stated with ATA start codon encodes a functional protein and that HopF2 has a measurable virulent and avirulent activities. In addition, we demonstrated that the activity of HopF2 is dependent on the presence of the myristoylation site, indicating membrane localization is required for correct function. The second effector we characterized is HopQ1-1. HopQ1-1 contains a putative nucleoside hydrolase domain. Here, we demonstrate that this gene also has virulent and avirulent functions. Moreover, mutation of the conserved residues present in the putative catalytic site abolished the activities of HopQ1-1.