Light affects motility and infectivity of Agrobacterium tumefaciens

Abstract

Response to changes in light conditions involves a variety of receptors that can modulate gene expression, enzyme activity and/or motility. For the study of light-regulated effects of Agrobacterium tumefaciens, we used a global analysis approach - proteomics - and compared the protein patterns of dark- and light-grown bacteria. These analyses revealed a significant reduction of FlaA and FlaB - proteins of the flagellum - when the cells were grown in light. The light effect was confirmed by SDS-PAGE with isolated flagella. Quantitative PCR experiments showed a 10-fold increase of the transcription level of flaA, flaB and flaC within 20 min after the transfer from light to darkness. Electron microscopy revealed that these molecular events result in a light-induced reduction of the number of flagella per cell. These changes have major physiological consequences regarding motility, which is considerably reduced with exposure to light. The inhibitory effect of light on the motility is not unique to A. tumefaciens and was also seen in other species of the Rhizobiaceae. Previous studies suggested that the flagella function is significant for bacteria-plant interactions and bacterial virulence. In our studies, light reduced the attachment of A. tumefaciens to tomato roots and the virulence of the bacteria in a cucumber infection assay.

Light regulates attachment, exopolysaccharide production, and nodulation in Rhizobium leguminosarum through a LOV-histidine kinase photoreceptor

“…S3A). Some components of the flagella were more abundant in dark-grown than in irradiated cells, as previously observed in Agrobacterium tumefaciens (31). The observed protein bands were identified by mass spectrometry as FlaA (30.97 kDa) and FlaB (31.18 kDa) flagellin proteins and hook components FlgE (44.44 kDa) and FlgK (52.13 kDa), products of the RL0718, RL0719, RL0728, and RL0729 genes, respectively.…”

Lights, Rhythms, Infection: The Role of Light and the Circadian Clock in Determining the Outcome of Plant–Pathogen Interactions

“…Bacteria cultured in the light had a reduced number of flagella (one or two compared with three to five in the dark) and exhibited reduced mobility in colony assays. Importantly, virulence was also directly affected by light; reduced root attachment was observed in tomato (Solanum lycopersicum) and smaller tumor formation in cucumber (Cucumis sativus) in the presence of light compared with darkness (Oberpichler et al, 2008). Two putative phytochromes and one cryptochrome have been identified in the A. tumefaciens genome (Goodner et al, 2001), but knockout mutants showed normal light-dependent regulation of Fla protein levels (Oberpichler et al, 2008), suggesting that an as yet unidentified photoreceptor may be involved in this process.…”

“…However, the vulnerability of the susceptible host and the virulence of the pathogen may vary both with developmental stage and time of day, thus affecting the outcome of the interaction. The importance of light with respect to the outcome of plant-pathogen interactions is becoming increasingly apparent; recent reports have shown direct effects of light on the both the defense response in the host and on the virulence of the attacking pathogen (Chandra-Shekara et al, 2006;Griebel and Zeier, 2008;Oberpichler et al, 2008). In addition, there is growing realization that circadian rhythms may play an important role in disease outcomes.…”

“…While it has long been known that motility affects the virulence of plant pathogens, a recent study by Oberpichler et al (2008) has provided evidence linking light perception and virulence via the control of cell motility. Analysis of the Agrobacterium tumefaciens C58 proteome revealed that the flaA and flaB flagellin subunits are significantly upregulated in dark-grown bacteria.…”

Red Light Activates the σB-Mediated General Stress Response ofBacillus subtilisvia the Energy Branch of the Upstream Signaling Cascade

“…Light regulation of motility in Agrobacterium tumefaciens (36) and Acinetobacter baylyi (M. Bitrian and B. C. Nudel, unpublished experiments) are recent examples. In this respect, it is relevant to mention that RsbP and RsbQ form a bicistronic operon, not only in B. subtilis (11) but in many other organisms as well, be it that the phosphatase domain can be substituted by other output modules like histidine protein kinases or guanylate cyclases (10).…”