Paying the Rent: How Endophytic Microorganisms Help Plant Hosts Obtain Nutrients

Johnston-Monje, D.; Castillo-Avila, D.K.; Raizada, M.N. & Becerra Lopez-Lavalle, L.A. (2019). Paying the Rent: How Endophytic Microorganisms Help Plant Hosts Obtain Nutrients. In: Moo-Young, Murray (edit). 2019. Comprehensive Biotechnology. 3rd Edition. Pergamon. Elsevier. (pp. 770-788)

Since plants first colonized land, endophytic bacteria and fungi have been inside them, contributing to their hosts' survival and evolution. Endophyte ecology is an active field of study seeking to understand principles of host strain selection and microbial provenance; although most plants were believed to take up endophytes from soil, transmission through seed or vegetative propagation are also important. This review discusses endophyte contributions to plant nutrient use efficiency (NUE) and their existing or potential applications to agriculture. Endophyte mechanisms to improve plant NUE include formation of extra-root hyphae for nutrient absorption; stimulating root growth; altering plant metabolism to promote nutrient uptake; fixing nitrogen; altering root exudates; colonizing rhizospheres and modifying soil chemistry directly, or even being digested by the root. Although many endophytic strains have been discovered, commercial endophytic inoculants are still mostly limited to arbuscular mycorrhizae, rhizobia, Azospirillum, Pseudomonas and Clavicipitaceous fungi sold in the form of infected grass seed. Wider adoption of endophyte products has been prevented by cheap fertilizer alternatives, unpredictable inoculant responses to host genotype or environmental conditions, competition from endogenous microbes, and poor inoculant establishment and persistence; technical difficulties that new plant microbiome ventures will have to overcome if they are to succeed. There is significant potential to improve agriculture if new strains continue to be discovered, mechanistic understanding of plant-microbe interactions increases, both endophytes and their hosts are genetically enhanced, relevant lab and greenhouse screens can be developed, and methods of effective formulation and deployment are engineered. Novel genes and metabolites from endophytes represent an additional largely untapped resource for future agricultural biotechnologies.