Shared Symbiotic Signaling

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Science  25 May 2012:
Vol. 336, Issue 6084, pp. 961
DOI: 10.1126/science.336.6084.961-c

Symbioses of plants with Rhizobium bacteria or mycorrhizal fungi find the microbes lodged in membrane-bound compartments within the host, called symbiosomes and arbuscules, respectively. Although functionally similar, they are morphologically distinct. Shared signaling components between these two symbioses suggest that the signaling pathway governing Rhizobium-legume interactions may have been co-opted from the more common mycorrhizal fungi symbiotic pathway. Ivanov et al. have now identified two members of the VAMP72 (vesicle-associated membrane protein) family, known for their involvement in exocytosis, as critical for the formation of the membrane interface that separates Rhizobium from its host. Medicago plants in which expression of the proteins was disrupted were deficient in the development of symbiosomes and arbuscules, but other aspects of the symbiotic system, such as the root nodule and infection threads, developed normally. VAMP72 proteins localized to exocytotic vesicles in developing symbiosomes. Thus, Rhizobium bacteria and mycorrhizal fungi establish their symbioses with similar subcellular mechanisms, although the fungal symbioses remain much more widespread than the symbioses involving bacteria.

Proc. Natl. Acad. Sci. U.S.A. 109, 10.1073/pnas.1200407109 (2012).

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