Search for: All records

Abstract By introducing novel capacities and functions, new genes and gene families may play a crucial role in ecological transitions. Mechanisms generating new gene families include de novo gene birth, horizontal gene transfer, and neofunctionalization following a duplication event. The ectomycorrhizal (ECM) symbiosis is a ubiquitous mutualism and the association has evolved repeatedly and independently many times among the fungi, but the evolutionary dynamics enabling its emergence remain elusive. We developed a phylogenetic workflow to first understand if gene families unique to ECM Amanita fungi and absent from closely related asymbiotic species are functionally relevant to the symbiosis, and then to systematically infer their origins. We identified 109 gene families unique to ECM Amanita species. Genes belonging to unique gene families are under strong purifying selection and are upregulated during symbiosis, compared with genes of conserved or orphan gene families. The origins of seven of the unique gene families are strongly supported as either de novo gene birth (two gene families), horizontal gene transfer (four), or gene duplication (one). An additional 34 families appear new because of their selective retention within symbiotic species. Among the 109 unique gene families, the most upregulated gene in symbiotic cultures encodes a 1-aminocyclopropane-1-carboxylate deaminase, an enzyme capable of downregulating the synthesis of the plant hormone ethylene, a common negative regulator of plant-microbial mutualisms. 

Summary Plant‐associated microbial communities can profoundly affect plant health and success, and research is still uncovering factors driving the assembly of these communities. Here, we examine how geography versus host species affects microbial community structure and differential abundances of individual taxa. We use metabarcoding to characterize the bacteria and eukaryotes associated with five, often co‐occurring species ofSarraceniapitcher plants (Sarraceniaceae) and three natural hybrids along the longitudinal gradient of the U.S. Gulf Coast, as well as samples fromS.purpureain Massachusetts. To tease apart the effects of geography versus host species, we focus first on sites with co‐occurring species and then on species located across different sites. Our analyses show that bacterial and eukaryotic community structures are clearly and consistently influenced by host species identity, with geographic factors also playing a role. Naturally occurring hybrids appear to also host unique communities, which are in some ways intermediate between their parent species. We see significant effects of geography (site and longitude), but these generally explain less of the variation among pitcher communities. Overall, inSarraceniapitchers, host plant phenotype significantly affects the pitcher microbiomes and other associated organisms.