Hyaloperonospora arabidopsidis (Hpa) candidate effectors suppress PTI enhancing plant susceptibility

GEORGINA FABRO; JONATHAN DG JONES

Toulouse, France

Congreso; Oomycete Molecular Genetics Network Meeting Toulouse 2010; 2010

Oomycete Molecular Genetics Network

We are focusing our studies in a set of candidate effectors from the oomyceteHyaloperonospora arabidopsidis (Hpa). This pathogen is an obligate biotroph of A. thalianathat is proposed uses a wide range of effectors to gain access to resources available in itshost. At the same time is able to avoid and/or suppress host defence responses, keeping thetissues alive until it completes its asexual and sexual reproductions. We have found that preinductionof strong PTI responses impairs the growth and reproduction of different Hpa raceson compatible A. thaliana Ecotypes. In contrast, Hpa is able to actively suppress PTI. Weobserved that plant tissues pre-infected with different Hpa races are less responsive,regarding levels of ROS burst and callose deposition, to bacterial and fungal PAMPs. In acollaborative effort with the ERA-PG Effectoromics consortium we have indentified andcloned several candidate effectors (small secreted proteins containing a signal peptide andRxLR motif). Taking advantage of a Heterologous (EDV) System that allow us to deliverone effector at the time via the Pseudomonas syringae (Pst) TTSS (Sohn et al., Plant Cell2007) we have assessed individually if a given Hpa effector could suppress PAMP triggeredimmunity (PTI). Our results indicate that around 50% of the effectors can suppress calloseaccumulation when delivered through the Pst ΔCEL mutant. Similarly, when we generatedtransgenic plants expressing constitutively 10 different Hpa effectors, we found in 7 out of 10cases that these plants show reduced ROS burst and callose deposition in response to flg22.These transgenics are also more susceptible to compatible Hpa races and to different P.syringae strains infections.