Photoreceptor that regulates flagella synthesis, exopolysaccharide production and biofilm formation in response to light. Also required for competitive nodulation. ATP + protein L-histidine = ADP + protein N-phospho-L-histidine. FMN binds covalently to cysteine after exposure to blue light (Probable). Mutant produces similar amounts of exopolysaccharides and shows no significant differences in the biofilm biomass between light and dark conditions. Mutant also forms a higher number of white nodules compared with the wild-type, independently of the illumination conditions.