Abstract
The biological function of the plant-microbiome system is the result of contributions from the host plant and microbiome members. The Populus root microbiome is a diverse community that has high abundance of β- and γ-Proteobacteria, both classes which include multiple plant-growth promoting representatives. To understand the contribution of individual microbiome members in a community, we studied the function of a simplified community consisting of Pseudomonas and Burkholderia bacterial strains isolated from Populus hosts and inoculated on axenic Populus cutting in controlled laboratory conditions. Both strains increased lateral root formation and root hair production in Arabidopsis plate assays and are predicted to encode for different functions related to growth and plant growth promotion in Populus hosts. Inoculation individually, with either bacterial isolate, increased root growth relative to uninoculated controls, and while root area was increased in mixed inoculation, the interaction term was insignificant indicating additive effects of root phenotype. Complementary data including photosynthetic efficiency, whole-transcriptome gene expression and GC-MS metabolite expression data in individual and mixed inoculated treatments indicate that the effects of these bacterial strains are unique and additive. These results suggest that the function of a microbiome community may be predicted from the additive functions of the individual members.
Highlights
Plants are associated with a diverse microbiota composed of thousands of interacting organisms that must be considered when studying plant function (Vandenkoornhuyse et al, 2015)
We chose two bacterial strains based on diverse taxonomy and abundant representation in the Populus microbiome (Gottel et al, 2011; Shakya et al, 2013) to study individual and cooperative effects on host plant growth (Table 1)
The data presented here supports the hypothesis that the bacterial strains in this study occupy different niches and have unique mechanisms to interact with the host that are independent of the alternate strain, indicating that the community phenotype in this 3-member system is predictable based on contributions of individual bacterial strains
Summary
Plants are associated with a diverse microbiota composed of thousands of interacting organisms that must be considered when studying plant function (Vandenkoornhuyse et al, 2015). The plant microbiome can modify nutrient acquisition (Jeong and Guerinot, 2009; Behie et al, 2012; Rousk et al, 2013; Oteino et al, 2015), pathogen resistance (Berendsen et al, 2012; Weston et al, 2012) and host ability to tolerate stress (Fernandez et al, 2012; Lau and Lennon, 2012) These functionalities are often realized through interactions with an exceedingly complex metagenome, consisting of millions of bacterial genes often with unknown host consequences. Numerous other reports (Hardoim et al, 2008; Bulgarelli et al, 2013; Coleman-Derr and Tringe, 2014; Guttman et al, 2014; Laksmanan et al, 2014; Lebeis, 2014) have outlined the diverse set of mechanisms through which individual bacteria can promote the growth of their host plants
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