Skip to main content
eScholarship
Open Access Publications from the University of California

Lotus hosts delimit the mutualism-parasitism continuum of Bradyrhizobium

  • Author(s): Regus, JU
  • Gano, KA
  • Hollowell, AC
  • Sofish, V
  • Sachs, JL
  • et al.

Published Web Location

https://doi.org/10.1111/jeb.12579
Abstract

© 2015 European Society For Evolutionary Biology. Symbioses are modelled as evolutionarily and ecologically variable with fitness outcomes for hosts shifting on a continuum from mutualism to parasitism. In a classic example, rhizobia fix atmospheric nitrogen for legume hosts in exchange for photosynthetic carbon. Rhizobial infection often enhances legume growth, but hosts also incur interaction costs because of root tissues and or metabolites needed to support symbionts in planta. Rhizobia exhibit genetic variation in symbiotic effectiveness, and ecological changes in light or mineral nitrogen availability can also alter the benefits of rhizobial infection for hosts. The net effects of symbiosis thus can range from mutualistic to parasitic in a context-dependent manner. We tested the extent of the mutualism-parasitism continuum in the legume-rhizobium symbiosis and the degree to which host investment can shape its limits. We infected Lotus strigosus with sympatric Bradyrhizobium genotypes that vary in symbiotic effectiveness. Inoculations occurred under different mineral nitrogen and light regimes spanning ecologically relevant ranges. Net growth benefits of Bradyrhizobium infection varied for Lotus and were reduced or eliminated dependent on Bradyrhizobium genotype, mineral nitrogen and light availability. But we did not detect parasitism. Lotus proportionally reduced investment in Bradyrhizobium as net benefit from infection decreased. Lotus control occurred primarily after infection, via fine-scale modulation of nodule growth, as opposed to control over initial nodulation. Our results show how divestment of symbiosis by Lotus can prevent shifts to parasitism.

Many UC-authored scholarly publications are freely available on this site because of the UC Academic Senate's Open Access Policy. Let us know how this access is important for you.

Main Content
Current View