Influence of hormonal alterations causing shade avoidance syndrome in the outcome of plant-pathogen interactions.

Hyaloperonospora arabidopsidis (Hpa) is an oomycete pathogen that causes Arabidopsis downy mildew. This obligate biotroph secretes multiple effector proteins to manipulate plant homeostasis, promoting infection through the interference with diverse metabolic and signaling pathways.We demonstrated that an effector protein from Hpa, named HaRxL106, directly interacts in the plant cell nucleus with the transcription factor BIM1 and the repressor protein Aux/IAA11, which participate in Brassinosteroid (BR) and Auxin signaling pathways, respectively. BIM1, but no IAA11, is required for HaRxL106 to increase the susceptibility of Arabidopsis to oomycete and also to bacterial pathogens. Moreover, we found that, even when grown in normal light conditions, plants expressing HaRxL106 display a Shade Avoidance-like Syndrome (SAS-like) that depends on the presence of BIM1. Furthermore, HaRxL106 increases the expression of a subset of BR and Auxin-related genes in a BIM1-dependient manner, a phenomenon that is likely responsible for the observed altered developmental pattern. Thus, we propose that BIM1 is a host susceptibility factor, manipulated by the effector protein HaRxL106 to alter the BR/Auxin signaling pathways triggering SAS, which negatively impacts on plant defense responses. In this poster, continuing the oral presentation given in Young Researchers Symposium on Plant Photobiology 2024, we present mostly the results of our studies on HaRxL106-IAA11 interaction.