Transcript profiling upon ethanol-induced expression of Xcv type 3- effector xopB in A. thaliana

The bacterial pathogen Xanthomonas campestris pv. vesicatoria 85-10 (Xcv) translocates about 30 type 3 effector proteins (T3Es) into pepper plants (Capsicum annuum) to suppress its immune responses. Among them is XopB which was previously shown to interfere with cell wall-bound invertase (CwInv) and sugar-mediated defence responses. Transgenic Arabidopsis thaliana lines expressing xopB under control of an ethanol inducible promotor were generated to investigate the in planta activity of this effector protein in more depth. The microarray analysis revealed that expression of the bacterial T3E XopB in A. thaliana plants causes immediate and massive reprogramming of transcription resulting in the alteration of the hormonal homeostasis and imbalances in signalling cascades. Further analyses unravelled that XopB modifies the pathogen associated molecular pattern (PAMP)-triggered calcium signature and inhibits the burst of reactive oxygen species (ROS). For microarray analyses, five week old transgenic plants (# 10, 12, 27) and wild-type plants were watered with 10 ml 1% (v/v) ethanol per pot after light has switch on in the climate chamber. Leaves from individual plants were harvested 4 h after treatment and immediately frozen in liquid nitrogen. Development of phenotypic changes was monitored and leaves of plants showing comparable phenotypes were pooled into 3 replicates.