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

Proc Natl Acad Sci U S A. 2012 Jul 24;109(30):12135-40. doi: 10.1073/pnas.1121292109. Epub 2012 Jul 5.


Rhizobium leguminosarum is a soil bacterium that infects root hairs and induces the formation of nitrogen-fixing nodules on leguminous plants. Light, oxygen, and voltage (LOV)-domain proteins are blue-light receptors found in higher plants and many algae, fungi, and bacteria. The genome of R. leguminosarum bv. viciae 3841, a pea-nodulating endosymbiont, encodes a sensor histidine kinase containing a LOV domain at the N-terminal end (R-LOV-HK). R-LOV-HK has a typical LOV domain absorption spectrum with broad bands in the blue and UV-A regions and shows a truncated photocycle. Here we show that the R-LOV-HK protein regulates attachment to an abiotic surface and production of flagellar proteins and exopolysaccharide in response to light. Also, illumination of bacterial cultures before inoculation of pea roots increases the number of nodules per plant and the number of intranodular bacteroids. The effects of light on nodulation are dependent on a functional lov gene. The results presented in this work suggest that light, sensed by R-LOV-HK, is an important environmental factor that controls adaptive responses and the symbiotic efficiency of R. leguminosarum.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Bacterial Adhesion / physiology*
  • Bacterial Adhesion / radiation effects
  • Base Sequence
  • Biofilms / growth & development
  • Blotting, Western
  • Flagella / metabolism
  • Gentian Violet
  • Histidine Kinase
  • Light*
  • Microscopy, Electron, Scanning
  • Molecular Sequence Data
  • Peas / microbiology*
  • Photoreceptors, Microbial / metabolism*
  • Plant Root Nodulation / physiology*
  • Plant Root Nodulation / radiation effects
  • Polysaccharides, Bacterial / metabolism
  • Protein Kinases / genetics
  • Protein Kinases / metabolism
  • Protein Structure, Tertiary / genetics
  • Real-Time Polymerase Chain Reaction
  • Rhizobium leguminosarum / physiology*
  • Rhizobium leguminosarum / radiation effects
  • Rhizobium leguminosarum / ultrastructure
  • Sequence Alignment
  • Sequence Analysis, DNA
  • Statistics, Nonparametric
  • Symbiosis*


  • EPSI polysaccharide
  • Photoreceptors, Microbial
  • Polysaccharides, Bacterial
  • Protein Kinases
  • Histidine Kinase
  • Gentian Violet