Role of plant growth-promoting bacteria (PGPB) in enhancing phenolic compounds biosynthesis and its relevance to abiotic stress tolerance in plants: a review

Biofortification of plants using Plant Growth-Promoting Bacteria (PGPB) represents a promising strategy in sustainable agriculture. This paper discusses the PGPB action in the context of their impact on phenolic compounds biosynthesis and the prospects for their application in agriculture. So far, no review article has summarized the significance of PGPB in increasing phenolic compounds in plants. PGPB, such as Pseudomonas, Bacillus, and Azospirillum, promote plant growth by producing phytohormones, enhancing nutrient availability, and stimulating the biosynthesis of secondary metabolites through the activation of Induced Systemic Resistance (ISR). The activation of ISR (Induced Systemic Resistance) by PGPB stimulates the phenylpropanoid pathway, which is the primary biosynthetic route for polyphenolic compounds, including phenolic acids and flavonoids, in plants. Studies indicate that PGPB may increase phenolic compounds content from 9% to over 200%, while simultaneously improving antioxidant activity. Through the secretion of phenolic compounds, PGPB also can mitigate abiotic stresses such as drought, salinity and heavy metal contamination. Among the phenolic compounds whose production in various plant parts can be stimulated by PGPB are flavonoids, such as quercetin, procyanidin B1, EGCG, and catechin, and phenolic acids, including caffeic acid, ferulic acid, and chlorogenic acid. Advancements in omics research will enable a more precise investigation of the impact of PGPB, including endophytic bacteria, on the biosynthetic pathways of phenolic compounds. In the future, this will translate into improved efficiency in stimulating the production of these compounds. Nevertheless, even now, the use of PGPB offers a sustainable alternative to genetic engineering, reducing reliance on chemical inputs in agriculture.