Foliar mycoendophytome of an endemic plant of the Mediterranean biome (Myrtus communis) reveals the dominance of basidiomycete woody saprotrophs.

Aline Bruna M Vaz,Rodrigo B Kato,Carlos A Rosa,Gabriel Quintanilha-Peixoto,Fernanda Badotti,Felipe F Silva,Inmaculada Sampedro,Juan A Ocampo,Aristóteles Góes-Neto,Anderson Carmo,Paula Luize C Fonseca,Jose A Siles,Vasco Azevedo

doi:10.7717/peerj.10487

Abstract

The true myrtle, Myrtus communis, is a small perennial evergreen tree that occurs in Europe, Africa, and Asia with a circum-Mediterranean geographic distribution. Unfortunately, the Mediterranean Forests, where M. communis occurs, are critically endangered and are currently restricted to small fragmented areas in protected conservation units. In the present work, we performed, for the first time, a metabarcoding study on the spatial variation of fungal community structure in the foliar endophytome of this endemic plant of the Mediterranean biome, using bipartite network analysis as a model. The local bipartite network of Myrtus communis individuals and their foliar endophytic fungi is very low connected, with low nestedness, and moderately high specialization and modularity. Similar network patterns were also retrieved in both culture-dependent and amplicon metagenomics of foliar endophytes in distinct arboreal hosts in varied biomes. Furthermore, the majority of putative fungal endophytes species were basidiomycete woody saprotrophs of the orders Polyporales, Agaricales, and Hymenochaetales. Altogether, these findings suggest a possible adaptation of these wood-decaying fungi to cope with moisture limitation and spatial scarcity of their primary substrate (dead wood), which are totally consistent with the predictions of the viaphytism hypothesis that wood-decomposing fungi inhabit the internal leaf tissue of forest trees in order to enhance dispersal to substrates on the forest floor, by using leaves as vectors and as refugia, during periods of environmental stress.

Highlights

Mediterranean Forests, Woodlands and Scrubs comprise a distinct biome of the Palearctic Biogeographic Realm (Olson et al, 2001)
Besides Myrtus communis, the following plants were commonly encountered in the sampling site: Quercus suber, Quercus faginea, Smilax aspera, Pistacia lentiscus, Chamaerops humilis, Pteridium aquilinum, Brachypodium retusum, Dactylis hispanica, Phlomis purpurea, Rubus ulmifolius and Cistus salvifolius (Pérez Latorre et al, 2004)
The network had order (N) = 56 nodes and size (M) = 93 edges. As it is a bipartite network, the lower level (LL) was composed of 11 Myrtus communis distinct individual plants, and the higher level (HL) encompassed 44 different fungal taxa (MOTUs), as identified by bioinformatics analyses, followed by an extensive manual curation. Excluding those assigned as undefined or incertae sedis, fungal endophyte MOTUs were classified into 44 putative species in 28 genera, 23 families, 16 orders, 11 classes, five subphyla and two phyla (Table 2)

Summary

Introduction

Mediterranean Forests, Woodlands and Scrubs comprise a distinct biome of the Palearctic Biogeographic Realm (Olson et al, 2001). Amongst the distinct ecoregions of this biome, the Southwestern Mediterranean sclerophyllous and mixed forests ecoregion is characterized by old crystalline substrates, such as granite, quartzite, and marble, with hot and dry summers and relatively mild and humid winters (Olson et al, 2001). These forests are mainly composed of evergreen broadleaves trees and shrubs such oaks, true myrtle (Myrtus communis), laurel and even two endemic palms, which give a unique subtropical feature to these dry, warm coastal landscapes occurring all around the Mediterranean Sea (Regato, 2001). M. communis is the only species of the tribe Myrtae of the family Myrtaceae that occurs in Europe (Vasconcelos et al, 2017), with a typical circum-Mediterranean geographic distribution (Migliore et al, 2012)

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Conclusion