CONICET | Buscador de Institutos y Recursos Humanos

Light is an important source of information for many different organisms. In plants and other photosynthetic organisms phytochrome photoreceptor proteins regulate functions related to growth and development. Bacteriophytochromes, the bacterial phytochromes, are found in both photosynthetic and nonphotosynthetic bacteria, including pathogens, although their role is still poorly understood. Xanthomonas campestris pv. campestris (Xcc), the causal agent of black rot of crucifers, is a plant pathogen of worldwide economic relevance. The Xcc genome encodes one putative bacteriophytochrome (phy). Our results suggest that light modulates biofilm formation through Phy. Furthermore we have established that mutation of phy leads to altered levels of xanthan polysaccharide, which is a virulence factor also involved in biofilm formation. Complementation of the mutant strain with a multicopy plasmid harboring phy restores these phenotypes. Moreover, the complemented strain produces significantly lower xanthan than the wild-type strain. Endoglucanase assays do not show differences between the wild-type an the mutant strains. However, the complemented strain exhibits lower endoglucanase levels, suggesting that Phy is acting as a negative regulator. Our in planta results also show that phy mutant is more virulent than the wild-type strain. This result can be explained because the mutant is able to keep the stomata open for much longer times. Callose synthesis studies during infection show that phy mutant has significant reduced callose levels compared to wild-type strain. In summary, our results show that Xcc Phy is involved in light-sensing activities and it regulates several in vitro phenotypes and it is also involved in several in planta phenotypes related to virulence. This work comprise the first evidence of a non-photosynthetic bacterial bacteriophitochrome regulating lightdependant phenotypes.

enviar mensaje