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Seeing the light: The roles of red and blue light sensing in bacterial plant pathogens

Gwyn Beattie: Iowa State University

<div>Plants collect, concentrate and conduct light throughout their tissues, thus enhancing light availability to their resident microbes. These microbes have evolved mechanisms of photosensing to modify their behavior in response to light cues. Many plant microbes have both far-red/red- and blue light-sensing proteins, and while the biochemical properties of these proteins are shared among organisms, we are only beginning to understand their biological roles in microbial interactions with plants. Unlike red and blue light, far-red light escapes absorption by photosynthetic tissues and is available for extensive redistribution through plants. Recent studies with foliar bacterial pathogens demonstrate that far-red light functions as a potent signal that influences global gene expression. Moreover, far-red light-sensing proteins contribute to suppressing virulence and behaviors such as swarming motility that influence the virulence of these pathogens. Blue light-sensing proteins also contribute to suppressing bacterial virulence, suppressing plant defenses, and increasing pathogen adherence to leaves and preventing entry, as well as to enhancing symbioses by a nitrogen-fixing symbiont. An increased understanding of how photosensing contributes to the evasion of light-mediated plant defenses and integrates with pathogen responses to co-occurring environmental stresses is increasing our appreciation of the biological significance of photosensing in plant microbe lifecycles.</div>