Expression of Xanthomonas campestris pv. vesicatoria Type III Effectors in Yeast Affects Cell Growth and Viability

Abstract

The gram-negative bacterium Xanthomonas campestris pv. vesicatoria is the causal agent of spot disease in tomato and pepper. X. campestris pv. vesicatoria pathogenicity depends on a type III secretion system delivering effector proteins into the host cells. We hypothesized that some X. campestris pv. vesicatoria effectors target conserved eukaryotic cellular processes and examined phenotypes induced by their expression in yeast. Out of 21 effectors tested, 14 inhibited yeast growth in normal or stress conditions. Viability assay revealed that XopB and XopF2 attenuated cell proliferation, while AvrRxo1, XopX, and XopE1 were cytotoxic. Inspection of morphological features and DNA content of yeast cells indicated that cytotoxicity caused by XopX and AvrRxo1 was associated with cell-cycle arrest at G0/1. Interestingly, XopB, XopE1, XopF2, XopX, and AvrRxo1 that inhibited growth in yeast also caused phenotypes, such as chlorosis and cell death, when expressed in either host or nonhost plants. Finally, the ability of several effectors to cause phenotypes in yeast and plants was dependent on their putative catalytic residues or localization motifs. This study supports the use of yeast as a heterologous system for functional analysis of X. campestris pv. vesicatoria type III effectors, and sets the stage for identification of their eukaryotic molecular targets and modes of action.

Identification of Novel Coxiella burnetii Icm/Dot Effectors and Genetic Analysis of Their Involvement in Modulating a Mitogen-Activated Protein Kinase Pathway

“…6B). Similar to our results, it was shown previously that the Xanthomonas campestris effector XopC does not inhibit yeast growth, but when it was examined in the presence of caffeine, it caused a strong growth inhibition (84). Notably, this effector was found to contain a HAD domain (Fig.…”

“…Notably, this effector was found to contain a HAD domain (Fig. 6A), and mutagenesis of conserved amino acids of this domain abolished the growth inhibition by XopC on yeast growth (84). The results showing the importance of the HAD domain for the activity of the C. burnetii CBU1676 and CBU0885 effectors and the analysis in yeast which indicates that these two effectors modulate a MAP kinase pathway suggest that these two effectors modulate the phosphorylation state of one or more components in the MAP kinase pathway.…”

A TAL effector repeat architecture for frameshift binding

“…Alternatively, our computational search of available OsSWEET14 promoter sequences raises the possibility that this potent virulence factor might favour colonization of Xoo on the different rice species O. sativa and O. brachyantha. So far, the possibility that TALEs of one bacterial strain support virulence in different host species has not been explored, but it is typical for type III effectors that they function in different plants and even non-plants 51,52 . Further analysis of natural TALEs with aberrant repeats and their target promoters will clarify the role of these unique virulence factors for the pathogen.…”

Five Xanthomonas type III effectors suppress cell death induced by components of immunity-associated MAP kinase cascades

“…This is in agreement with previous findings showing that expression of AvrBs1 in yeast causes sensitivity to NaCl and sorbitol that are known inducers of the HOG pathway. 28 In conclusion, our screen identified five Xanthomonas effectors that suppressed cell death induced by components of immunity-associated MAP kinase cascades. Furthermore we found that AvrBs1 suppresses activation of the HOG MAPK pathway in yeast, suggesting that this effector targets a signaling component that is conserved in eukaryotic organisms.…”