Pseudomonas syringae type III effector AvrRpt2 alters Arabidopsis thaliana auxin physiology

Abstract

The Pseudomonas syringae type III effector AvrRpt2 promotes bacterial virulence on Arabidopsis thaliana plants lacking a functional RPS2 gene (rps2 mutant plants). To investigate the mechanisms underlying the virulence activity of AvrRpt2, we examined the phenotypes of transgenic A. thaliana rps2 seedlings constitutively expressing AvrRpt2. These seedlings exhibited phenotypes reminiscent of A. thaliana mutants with altered auxin physiology, including longer primary roots, increased number of lateral roots, and increased sensitivity to exogenous auxin. They also had increased levels of free indole acetic acid (IAA). The presence of AvrRpt2 also was correlated with a further increase in free IAA levels during infection with P. syringae pv. tomato strain DC3000 (PstDC3000). These results indicate that AvrRpt2 alters A. thaliana auxin physiology. Application of the auxin analog 1-naphthaleneacetic acid promoted disease symptom development in PstDC3000-infected plants, suggesting that elevated auxin levels within host tissue promote PstDC3000 virulence. Thus, AvrRpt2 may be among the virulence factors of P. syringae that modulate host auxin physiology to promote disease.disease ͉ indole acetic acid ͉ pathogen ͉ virulence ͉ host physiology

The Pseudomonas syringae Type III Effector AvrRpt2 Promotes Pathogen Virulence via Stimulating Arabidopsis Auxin/Indole Acetic Acid Protein Turnover

“…Similar to the plant defense hormones SA and jasmonic acid, auxin differentially regulates the outcomes of plant-pathogen interactions depending on the life styles of the pathogens (Kazan and Manners, 2009;Robert-Seilaniantz et al, 2011). During infection by Pst, the free indole acetic acid level increased and application of auxin promoted disease symptom development (O'Donnell et al, 2003;Chen et al, 2007;Wang et al, 2007). Consistently, the type III effector AvrRpt2 modulates host auxin physiology and signaling as a potential virulence strategy (Chen et al, 2007).…”

“…Consistent with auxin's role in plant disease resistance, we have found that the P. syringae effector AvrRpt2 augments host auxin biosynthesis and signaling and alters auxin physiology (Chen et al, 2007). Transgenic Arabidopsis plants expressing AvrRpt2 exhibit phenotypes reminiscent of auxin mutants with altered auxin physiology, including elongated primary roots and increased numbers of lateral roots, increased response to exogenously applied auxin, and enhanced accumulation of free indole acetic acid during P. syringae infection (Chen et al, 2007).…”

“…Our results raise the possibility that the effect of AvrRpt2 on AXR2 protein stability might be the result of increased auxin level in AvrRpt2-transfected protoplasts or transgenic plants. We have previously detected an increase of auxin level in AvrRpt2 transgenic plants (Chen et al, 2007). To test this hypothesis, we treated AXR2-HAtransfected cells with gradually increased concentrations of NAA and examined AXR2 protein levels.…”

“…Transgenic Arabidopsis plants expressing AvrRpt2 exhibit phenotypes reminiscent of auxin mutants with altered auxin physiology, including elongated primary roots and increased numbers of lateral roots, increased response to exogenously applied auxin, and enhanced accumulation of free indole acetic acid during P. syringae infection (Chen et al, 2007). Transient expression of AvrRpt2 in protoplasts promotes auxin-responsive gene expression (Chen et al, 2007). AvrRpt2 is a Cys protease that is active in plant cells, and several host targets of AvrRpt2 have been identified (Axtell et al, 2003;Chisholm et al, 2005).…”

“…Recent progress has revealed the cross talk of signaling pathways between classical phytohormones, such as auxin, abscisic acid (ABA), cytokinins, and brassinosteroids, and plant disease resistance or susceptibility (Spoel and Dong, 2008;Grant and Jones, 2009;Kazan and Manners, 2009;Robert-Seilaniantz et al, 2011). Free auxin levels increase in plants infected with P. syringae or Xanthomonas spp., and application of exogenous auxin promotes disease susceptibility (O'Donnell et al, 2003;Chen et al, 2007;Wang et al, 2007). Inappropriate activation of ABA biosynthesis and signaling disrupts plant resistance to several pathogens (de Torres Zabala et al, 2009;Fan et al, 2009).…”