The roles of endophytes in modulating crop plant development

Endophytes are the microorganisms which mutually live inside healthy plant tissues, playing important roles in promoting plant growth and providing adaptation toward various environments. Bacteria and fungi are the two major groups that have been recognized as endophytes. Endophytes have been reported to promote plant growth by improving nutrient uptake and solubilization of phosphate, potassium, nitrogen, and iron. Endophytes also biologically fix nitrogen and make it available to host plants. Endophytes produce growth-promoting phytohormones, including auxins, cytokinins, and gibberellins, and modulate the level of the growth-inhibiting hormone, ethylene, by producing 1-aminocyclopropane-1-carboxylate deaminase activity. Many endophytes also share antifungal activity and have been reported to protect plants from pathogenic microorganisms. Endophytic species of Bacillus are known to produce antifungal lipopeptides; species of Pseudomonas and Burkholderia produce a variety of antifungal secondary metabolites and HCN and protect plants from fungal infection. Thus the endophytes are natural inhabitants of plants that can be exploited as biofertilizers and biocontrol agents for sustainable cultivation of crop plants.