Bacteriophytochromes from Pseudomonas syringae pv. tomato DC3000 modulate the early stages of plant colonization during bacterial speck disease

Abstra t Living organisms have evolved the ability to perceive and respond to light of different wavelengths within the visible spectrum by the generation of photoreceptor proteins. Recent studies revealed the participation of these proteins in the virulence of plant pathogenic bacteria. Pseudomonas syringae pv. tomato DC3000 (Pto) is responsible for the bacterial speck, which affects tomato crops. Pto genome contains two genes encoding red/far-red light photoreceptors (BphP1: PSPTO_1902 and BphP2: PSPTO_2652). This work demonstrates the participation of Pto phytochromes and light in the bacterial physiology and during the interaction with tomato plants. We found that Pto phytochromes are implicated in the control of some features related with the bacteria capability to enter into the plant apoplast and cause bacterial speck disease, such as motility, biofilm formation, adhesion and emulsification capability. Red light and bacteriophytochromes are important during the early colonization stage of tomato phyllosphere, affecting Pto virulence. In addition, the development of disease symptoms in infiltrated leaflets is affected by light, which may be the consequence of type-two secretion system regulation.