PerspectiveEvolution

Many roads to convergence

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Science  13 Jul 2018:
Vol. 361, Issue 6398, pp. 125-126
DOI: 10.1126/science.aau2409

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Summary

Many plants form specialized symbiotic root structures, called nodules, that harbor beneficial associations with nitrogen-fixing bacteria in the genera Rhizobium or Frankia (see the photo). How this nitrogen-fixing root nodule (NFN) symbiosis arose repeatedly during plant evolution is an age-old mystery: It shows signatures of convergence (the repeated emergence of similarity during evolution) yet builds on similar gene sets in phylogenetically distant plants. On page 144 of this issue, Griesmann et al. (1) sequenced the genomes of 10 plant species to reveal the genetic correlates of the origin and loss of NFN symbiosis. Their work reveals intricate gain and loss patterns of symbiosis-associated genes, calling for new models to explain convergent evolution.