Leaf nodule symbiosis: function and transmission of obligate bacterial endophytes

The Potato Yam Phyllosphere Ectosymbiont Paraburkholderia sp. Msb3 Is a Potent Growth Promotor in Tomato

“…Many members of Burkholderia s.l. have been isolated and observed in association to plants; some as pathogens (Burkholder, 1942(Burkholder, , 1950Lee et al, 2005) or as plant growth promoting rhizobacteria (PGPR) and β-rhizobia (Estrada-De Los Santos et al, 2001;Compant et al, 2008;Suarez-Moreno et al, 2012) and others as secondary metabolite producing wardens of their host plant (Van Oevelen, 2002;Lemaire et al, 2011;Carlier and Eberl, 2012;Lemaire et al, 2012a,b;Sieber et al, 2015;Carlier et al, 2016;Pinto-Carbo et al, 2018). The later are of exceptional nature, as they usually colonize glandular structures within the leaf mesophyll, referred to as "leaf-nodules."…”

“…The specificity of the symbiosis, however, confines efforts trying to transfer these traits or species to economically important crop plants. Recently, the occurrence of the leaf nodule symbiosis has been described in the yam family, Dioscoreaecea (Carlier et al, 2017;Pinto-Carbo et al, 2018;De Meyer et al, 2019). The sansibar yam, Dioscorea sansibarensis, is considered the only species of the monocot family, in which nodule formation occurs, and interestingly, the facultative symbiont, Orrella dioscoreae, carries a large genome and can be cultured.…”

Early steps in the evolution of vertical transmission revealed by a plant-bacterium symbiosis

“…Leaf nodule symbioses represent some of the most intimate associations between plants and bacteria. The symbionts reside in dedicated structures called leaf glands or nodules, and are transmitted between generations via seeds [7]. Most leaf nodule symbioses are found in species of the Rubiaceae ( Psychotria and Pavetta ) and Primulaceae ( Ardisia ) families, and their symbionts are members of the Burkholderiaceae family of β-proteobacteria.…”

“…Burkholderia) species cannot be cultured outside of their host and bacteria-free Psychotria kirkii and Ardisia crenata display severe growth defects [8, 9]. This co-dependence between host and symbiont is likely the result of co-evolution over several million years, compounded by small effective population sizes and genetic drift [7]. Typical of vertically-transmitted symbiotic bacteria, Ca .…”

“…Leaves of D. sansibarensis display prominent acumens or ‘drip-tips’, harboring high titers (>10 9 cfu/g) of Orrella dioscoreae ( O. dioscoreae ), a newly described species of the Alcaligenaceae family [15]. Similar to leaf nodule symbioses in dicot species, the bacteria are hosted extracellularly in the leaf gland and do not invade the mesophyll or vasculature of the host and do not spread systemically [7]. In contrast to other leaf nodule symbioses, O. dioscoreae can be cultured [15].…”