Innovations in two genes kickstarted the evolution of nitrogen-fixing nodules.

The root nodule symbiosis between plants and nitrogen-fixing bacteria is a fascinating trait limited to several plant species. Given the agronomic potential of transferring this symbiosis to nonleguminous crops, the symbiosis has attracted researchers' attention for over a century. The origins of this symbiosis can be traced back to a single ancestor, around 110 million years ago. Recent findings have uncovered that adaptations in a receptor complex and the recruitment of the transcription factor Nodule Inception (NIN) are among the first genetic adaptations that allowed this ancestor to respond to its microsymbiont. Understanding the consequences of recruiting these genes provides insights into the start of this complex genetic trait.
Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Rene Geurts reports financial support was provided by Engineering the Nitrogen Symbiosis for Africa (ENSA), which is funded by Bill & Melinda Gates Agricultural Innovations. Rene Geurts reports financial support was provided by Bill & Melinda Gates Foundation, and the Foreign, Commonwealth and Development Office. Rik Huisman reports financial support was provided by Nederlandse Organisatie voor Wetenschappelijk Onderzoek.
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