Soil is a major source of bacterial symbionts in plants. Select bacteria colonize the rhizosphere and subsequently the endosphere, where they can infect the entire host and reside asymptomatically as endophytes. The composition of the bacterial endosymbiont community is influenced by the soil microbial community, environmental factors and host biology. Jatropha curcas (Euphorbiaceae) is a drought-tolerant biodiesel crop plant that is native to dry areas of Central America. We investigated how soil factors and local environmental conditions contribute to the endophytic bacterial community assembly in J. curcas seedlings in a field and greenhouse setting. We grew jatropha seedlings in three sites across the Azuero peninsula of Panama as well as in soil from those areas in a greenhouse. We later extracted DNA from the soils and from the roots and leaves of the plants to create 16S libraries of the symbiotic bacterial community. We then created a model to determine the contribution of environmental measures and soil microbial diversity to the endosymbiont community.
Results/Conclusions
Plants assembled unique endophytic communities at different sites in the field within leaf and root tissues, but greenhouse-grown plants using soil from these localities showed a convergence of endophytic communities. Roots hosted more diverse communities in the field than in the greenhouse, but this pattern did not hold true for leaves. We found that the environmental measures and the soil microbial community each explained a significant amount of variation in the root bacterial community structure (24.24% and 11%, respectively). Our model selected K, P, Rainfall, Mg, Ca and Al as significant environmental predictors of root bacterial community. The bacterial microbiome of J. curcas is plastic and the endosymbiont community may vary by the host’s location and stress level. In the field, where the ambient environment was not constant and where environmental stresses are the strongest, we saw divergence in community based on location. However, this divergence was not observed to the same degree in the greenhouse. One interpretation of this is that stress alters bacterial colonization method and success rates. Furthermore, our model selected major plant nutrients and rainfall as significantly explaining endosymbiont community composition. Therefore, different agricultural practices may have predictable effects on a plant’s endosymbiont community.