An endosymbiosis in plant shoots based on an ankyrin repeat protein

Abstract Chemical-based, modern agriculture is harmful to the environment, consuming fossil fuels, producing eutrophication, killing pollinators, and threatening human health. Because sustainable alternatives based on soil- or root-associated microorganisms are unreliable, new tools are necessary. Methylorubrum extorquens DSM13060 colonizes plant meristematic cells and aggregates around nuclei. The endosymbiont promotes plant growth without producing hormones but encodes putative nucleomodulins. We examined the role of an ankyrin-repeat protein (Ank) in the endosymbiosis. Ank interacted with 46 host proteins, expressed mainly in the cytoplasm and nucleus. Ank had a viral motif and interacted with defense-associated proteins. Deletion strain, Δ ank , lacked the capacity for colonization, indicating that interaction of Ank with plant proteins is needed. The plant-growth promotion capacity was lost in Δ ank , confirming the role of endosymbiosis behind this effect. Our results characterize Ank as a key that unlocks the beneficial traits of endosymbiosis, portraying a new mechanism of plant-associated bacteria for sustainable agriculture.