Abstract
Symbioses between plants and microorganims have been fundamental in the evolution of both groups. The endophytic bacteria associated with conifers have been poorly studied in terms of diversity, ecology, and function. Coniferous trees of the genera Larix, Pseudotsugae, Picea and mainly Pinus, are hosts of many insects, including bark beetles and especially the Dendroctonus species. These insects colonize and kill these trees during their life cycle. Several bacteria detected in the gut and cuticle of these insects have been identified as endophytes in conifers. In this study, we characterized and compared the endophytic bacterial diversity in roots, phloem and bark of non-attacked saplings of Pinus arizonica and P. durangensis using 16S rRNA gene pyrosequencing. In addition, we evaluated the degree of taxonomic relatedness, and the association of metabolic function profiles of communities of endophytic bacteria and previously reported gut bacterial communities of D. rhizophagus; a specialized bark beetle that colonizes and kills saplings of these pine species. Our results showed that both pine species share a similar endophytic community. A total of seven bacterial phyla, 14 classes, 26 orders, 43 families, and 51 genera were identified. Enterobacteriaceae was the most abundant family across all samples, followed by Acetobacteraceae and Acidobacteriaceae, which agree with previous studies performed in other pines and conifers. Endophytic communities and that of the insect gut were significantly different, however, the taxonomic relatedness of certain bacterial genera of pines and insect assemblages suggested that some bacteria from pine tissues might be the same as those in the insect gut. Lastly, the metabolic profile using PICRUSt showed there to be a positive association between communities of both pines and insect gut. This study represents the baseline into the knowledge of the endophytic bacterial communities of two of the major hosts affected by D. rhizophagus.
Highlights
Symbiosis has been recognized as a “key driver” force in the species evolutionary process
A biological replicate corresponding to the bark of Arizona pine was discarded given that it presented an insufficient number of reads
A total of seven phyla, 14 classes, 26 orders, 43 families, and 51 bacterial genera were identified in roots, phloem, and bark of Arizona and Durango pines samples
Summary
Symbiosis has been recognized as a “key driver” force in the species evolutionary process. Endophytic microorganisms of the endosphere, i.e., those that reside within the inner tissues of plants without causing any symptoms of disease (Hallmann et al, 1997), have enhanced plant tolerance to different biotic and abiotic factors and mediated the interaction with parasites (Reinhold-Hurek and Hurek, 2011; Hardoim et al, 2015; Hashem et al, 2016). Most of these studies have been carried out using culturedependent methods and traditional molecular techniques (e.g., molecular cloning, fingerprinting). Given that these approaches are limited in their statistical coverage, they can lead to biases in diversity characterization by the low number of sequences recovered. The application of generation sequencing (NGS) technologies overcomes these limitations and allows a better taxonomic and functional characterization of endophytic communities in conifers (Carrell and Frank, 2014, 2015; Carrell et al, 2016; Kaul et al, 2016; Rúa et al, 2016)
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