Role of leaf developmental stage on metabolomes and endophyte assemblages associated with tropical Rubiaceae plants

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Humberto Castillo-Gonzalez, University of Maryland, Fernanda R. Castro-Moretti and Ana P Alonso, University of North Texas, Phillip P.A. Staniczenko, National Socio-Environmental Synthesis Center (SESYNC), Jason Slot, Ohio State University, Priscila Chaverri, University of Costa Rica

Background/Question/Methods: Plants may play a role in selecting the lineages and functions of the fungal endophytes that inhabit them. Unfortunately, the mechanisms driving this process remain largely unexplored. It has been speculated that it is cued by the production of chemical compounds, however, to this date it is still unclear the ecological role played by plant secondary metabolites (PSM) in the assemblage of endophytic communities (EC). Plant metabolomes are differentiated by factors that also impact EC structure. There’s evidence that PSM distribution change dynamically in the plant tissues as fitness value and vulnerability change according to ontogeny. In this line, tissue developmental stage represents a suitable object of study to explore how maturation changes the plants chemical profile and if it affects fungal EC. If diversity between leaf development stage is significant, then: What are the selection mechanisms that shape the structure of the leaf-inhabiting fungi? The process might be facilitated by enrichment or exclusion of particular fungal lineages through chemical interactions. We hypothesize that in order to protect the tender foliage, the prevalence of PSM is higher in young leaves, limiting endophytic colonization. For this research, two old growth forests in Costa Rica were sampled. Fungal EC associated with young and mature leaves of several species of wild Rubiaceae were analyzed and studied to determine community structure. Library preparation was performed through ITS nrDNA metabarcoding (Ion Torrent) and diversity was assessed using a variety of packages in RStudio (i.e., DADA2, phyloseq, igraph). For the metabolomic assessment whole leaves where lyophilized and then grinded for quantification of targeted and untargeted metabolites, the powder was extracted and derived and then analyzed using LC-MS and GC-MS workflows.
Results/Conclusions: Our proposed ecological network analyses to model the community in the different stages revealed structural transformations. Diversity index analyses ascertained that Rubiaceae‐associated EC are affected by developmental stage: colonization frequency and species are higher in mature leaves than in juvenile. However, t-tests revealed no overall difference in chemoprofile as a function of leaf age. Our findings provide new insights into the mechanisms driving EC assemblage in tropical trees; however, in general, more research is needed to understand how the plants’ chemical profile shapes community structure of symbionts at ecological levels.