Mechanisms of nuclear suppression of host immunity by HaRxL44, an Arabidopsis downy mildew effector

MARIE-CECILE CAILLAUD; SHUTA ASAI; LENNART WIRTHMUELLER; SOPHIE J. M. PIQUEREZ; GEORGINA FABRO; JONATHAN D. G. JONES

Asilomar, Pacific Grove

Congreso; Oomycete Molecular Genetics Network Meeting; 2013

Oomycete Molecular Genetics Network

Plants are continuously exposed to microbial pathogen attacks but usually remain healthy because they are able to perceive microbes and then activate defence. Nonetheless, pathogens have evolved to overcome plant immunity by expressing effectors that increase host susceptibility, resulting in disease. Recent studies suggest that effectors may manipulate host transcription or other nuclear regulatory components for the benefit of the pathogen. However, the specific mechanisms by which these effectors promote susceptibility remain unclear. Out of two recent screenings, we identified 15 nuclear localized Hpa effectors (HaRxLs) that enhance plant susceptibility to pathogens. When stably expressed in planta, nuclear-HaRxLs cause diverse developmental phenotypes which highlight their interference with fundamental plant regulatory mechanisms. Results obtained in the large-scale yeast two-hybrid screen highlight that nuclear-HaRxLs interact preferentially with transcriptional regulators. In particular, HaRxL44 interacts with a component of Mediator, a major integrator of biotic stress responses, essential for plant nuclear immunity. We will present recent advances in our understanding on how HaRxL44 effector activates JA signalling at transcriptional level via its interaction with Mediator, in order to promote Hpa virulence.