The LOV Protein of <i>Xanthomonas citri</i> subsp. citri Plays a Significant Role in the Counteraction of Plant Immune Responses during Citrus Canker

<div><p>Pathogens interaction with a host plant starts a set of immune responses that result in complex changes in gene expression and plant physiology. Light is an important modulator of plant defense response and recent studies have evidenced the novel influence of this environmental stimulus in the virulence of several bacterial pathogens. <i>Xanthomonas citri</i> subsp. citri is the bacterium responsible for citrus canker disease, which affects most citrus cultivars. The ability of this bacterium to colonize host plants is influenced by bacterial blue-light sensing through a LOV-domain protein and disease symptoms are considerably altered upon deletion of this protein. In this work we aimed to unravel the role of this photoreceptor during the bacterial counteraction of plant immune responses leading to citrus canker development. We performed a transcriptomic analysis in <i>Citrus sinensis</i> leaves inoculated with the wild type <i>X. citri</i> subsp. citri and with a mutant strain lacking the LOV protein by a cDNA microarray and evaluated the differentially regulated genes corresponding to specific biological processes. A down-regulation of photosynthesis-related genes (together with a corresponding decrease in photosynthesis rates) was observed upon bacterial infection, this effect being more pronounced in plants infected with the <i>lov</i>-mutant bacterial strain. Infection with this strain was also accompanied with the up-regulation of several secondary metabolism- and defense response-related genes. Moreover, we found that relevant plant physiological alterations triggered by pathogen attack such as cell wall fortification and tissue disruption were amplified during the <i>lov-</i>mutant strain infection. These results suggest the participation of the LOV-domain protein from <i>X. citri</i> subsp. citri in the bacterial counteraction of host plant defense response, contributing in this way to disease development. </p>