Modulation in phenolic root exudate profile of Abelmoschus esculentus expressing activation of defense pathway.

Phenolics play a key role in communication between plants and microbes in the rhizosphere. In this study, shikimic, gallic, fumaric, ferulic, vanillic acid and quercetin in root exudates of Abelmoschus esculentus act as chemoattractants of endophytic Alcaligenes faecalis strains, BHU 12, BHU 16 and BHU M7. In vitro chemotaxis assay showed that BHU 12 expressed highest chemotactic movement (CFU ∼50×1012) towards A.esculentus root exudates followed by BHU 16 and BHU M7 (CFU∼ 9×1012), thereby confirming their ability to colonize the host rhizoplane region. However, BHU 16 expressed highest biofilm formation ability followed by BHU 12 and BHU M7. Assessment of chemotactic and biofilm formation potential towards individual phenolic acids revealed BHU 12 to be maximally attracted towards 1μM shikimic acid (2×1015) while BHU 16 towards 1mM vanillic acid (6.5×1012) and BHU M7 towards 1mM ferulic acid (3.5×1012), thereby confirming the phenolic acid components responsible for particularly attracting the endophytic isolates. Upon colonization, the endophytic isolates modified the phenolic profiles of root exudates in planta in a manner so as to plausibly attract more of the beneficial rhizospheric microbiota as well as self-fortification against pathogenic microbes. This hypothesis was verified by monitoring the changes in phenolic components of A. esculentus root exudate owing to S. rolfsii infection, a disastrous soil-borne pathogen. Thus, on the whole, the work provides intricate details of plant-endophyte interactions for biotic stress management through careful manipulation of root exudates, thereby aiding in sustainable agriculture.