Abstract
The rapid developments in the next-generation sequencing methods in the recent years have provided a wealth of information on the community structures and functions of endophytic bacteria. However, the assembly processes of these communities in different plant tissues are still currently poorly understood, especially in wild plants in natural settings. The aim of this study was to compare the composition of endophytic bacterial communities in leaves and roots of arcto-alpine pioneer plant Oxyria digyna, and investigate, how plant tissue (leaf or root) or plant origin affect the community assembly. To address this, we planted micropropagated O. digyna plants with low bacterial load (bait plants) in experimental site with native O. digyna population, in the Low Arctic. The endophytic bacterial community structures in the leaves and roots of the bait plants were analyzed after one growing season and one year in the field, and compared to those of the wild plants growing at the same site. 16S rRNA gene targeted sequencing revealed that endophytic communities in the roots were more diverse than in the leaves, and the diversity in the bait plants increased in the field, and was highest in the wild plants. Both tissue type and plant group had strong impact on the endophytic bacterial community structures. Firmicutes were highly abundant in the leaf communities of both plant types. Proteobacteria and Bacteroidetes were more abundant in the roots, albeit with different relative abundances in different plant groups. The community structures in the bait plants changed in the field over time, and increasingly resembled the wild plant endophytic communities. This was due to the changes in the relative abundances of several bacterial taxa, as well as species acquisition in the field, but with no species turnover. Several OTUs that were acquired by the bait plants in the field and represent phosphate solubilizing and diazotrophic bacterial taxa, suggesting major role in nutrient acquisition of these bacteria for this nonmycorrhizal plant, thriving in the nutrient poor arctic soils.
Highlights
All eukaryotes maintain a close relationship with diverse microorganisms
Plant tissue type was the major determinant of the diversity and community structure of endophytic bacterial communities
This is in agreement with other studies, where the endophytic bacterial communities were shaped by plant tissues and the major endophyte taxa in leaves differed from those in the roots (Bodenhausen et al, 2013; Checcucci et al, 2016; Robinson et al, 2016)
Summary
All eukaryotes maintain a close relationship with diverse microorganisms. Rapidly accumulating data indicates, that plant microbiome is a key determinant of plant health and productivity by providing a plethora of functional capacities (Brader et al, 2014; Hardoim et al, 2015). Abiotic and biotic factors influence the assembly of rhizospheric, phyllospheric, and endophytic bacterial communities Factors such as soil type (Conn and Franco, 2004; Bulgarelli et al, 2012), host plant species (Nissinen et al, 2012; Ding et al, 2013), plant age and genotype (Marques et al, 2014; Wagner et al, 2016), as well as plant developmental stage (Chaparro et al, 2014; Yuan et al, 2015) have all been shown to have a major effect on the endophytic bacterial community composition. The reported endophytic bacterial population densities are higher in roots (105–107 CFU g−1 of fresh weight) than in the leaves (103– 104 CFU g−1), likely reflecting the higher nutrient levels and less stressful conditions in the roots (reviewed by Compant et al, 2010)
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