P-378 - Root bacteria and Arabidopsis actively cooperate to promote phosphorus nutrition and growth

Plants interact dynamically with root-associated bacteria during phosphate malnutrition. Whether and how plants can actively engage bacteria for phosphorus acquisition and growth remain unknown. We show that ~20% root-associated bacteria can alleviate the phosphate starvation response (PSR) of Arabidopsis seedlings and promote plant growth by utilizing an insoluble inorganic phosphate. A close examination of a growth-promoting Acinetobacter guillouiae showed that Pi-deprived roots actively recruit this bacterium via malate, and this is essential for plant growth promotion and PSR alleviation. Pi-starved roots additionally stimulate bacterial phosphate homeostasis-related genes. Active Pi solubilization and Pi transport processes of the A. guillouiae bacterium are also required for promoting plant growth and alleviating PSR. A. guillouiae further cooperates with other root bacteria in a synthetic community to promote plant phosphorus nutrition and growth. Our findings suggest that active cooperation between Arabidopsis plants and root commensal bacterial members enable plants to utilize otherwise inaccessible phosphate.