Evolution and biogeography of actinorhizal plants and legumes: A comparison

The symbiosis between plants and nitrogen-fixing bacteria is widespread among legumes actinorhizal within the root nodule (NFN) clade. However, there are major differences, as well similarities, in symbioses Frankia those of their associated rhizobia. This review provides an overview NFN symbioses. We outline evolution biogeography compare contrast microsymbionts symbiotic processes. Within clade, a far greater number nodulated exists, compared with plants, have much wider biogeographical distribution. There genetic physiological differences free-living diazotrophic phylogenetically diverse rhizobia, most strains which unable to fix N2 ex planta. Actinorhizal nodules modified lateral roots central vascular system, whereas legume stem-like organs peripheral systems. Most contain symbiosomes, rather than infection threads found cells. Legumes control microsymbionts, Inverted Repeat Lacking Clade impose terminal differentiation on bacteroids. also effective processes for autoregulation nodulation downregulation fixation response high levels soil N. These features legume-rhizobia led increased efficiencies fixation. Synthesis. suggest that these characteristic symbiosis, specifically legumes' flexibility choice microsymbiont partner fixation, factors can explain why majority species Leguminosae retained ability nodulate how this has contributed evolutionary success.