Producing biomass that is tailored toward energy production, but that does not negatively impact food supply is one of the critical social-economical issues of the proposed US biofuel program. Poplar is considered as the model tree species for bioenergy feedstock production. Plants, however, live in close association with symbiotic microorganisms. We showed that specific strains of endophytic bacteria had a beneficial effect on the development and growth of poplar on marginal soils, resulting in a 30% increase in biomass production. To better understand the complex interactions between endophytes and poplar, including production of phytohormones, antibiotics to inhibit the growth of pathogens or ACC de-aminase activity to counteract the plant’s stress-ethylene response, the genomes of four plant growth promoting endophytic bacteria were sequenced. Genome annotation, analysis of metabolic properties, and comparisons with closely related non-endophytic bacteria resulted in the identification of several unique pathways by which endophytic bacteria can promote plant growth and health. Using directed mutagenesis we are presently examining the role of these pathways in plants growth and development.
In addition, the sequenced genome of Populus trichocarpa provides us with the unprecedented tools to study the interactions between poplar and its endophytic partners on the “omics” level, and to combine these data with results on plant growth, physiology, and biomass composition. This should result in a better understanding of the synergistic interactions between poplar and its growth promoting endophytes, which can be exploited to improve plant establishment and sustainable bioenergy feedstock production on marginal, non-agricultural land.