Novel biotechnological strategies to combat biotic stresses: polygalacturonase inhibitor (PGIP) proteins as a promising comprehensive option

Global climate change and combinatorial environmental stresses pose grave challenges to food security and agricultural sustainability. This calls for diverse and futuristic approaches for the development of crops with increased resilience to natural vagaries. Though innumerable strategies involving diverse genes/pathways are being deciphered in plants to aid stress mitigation, the hunt is still on. Furthermore, strategies that work to alleviate a combination of stresses are always pertinent. In this review, we discuss polygalacturonase inhibitor (PGIP) proteins as a plausible option to mitigate multiple biotic stresses. These are ubiquitous cell wall proteins that inhibit the pectin-depolymerizing activity of cell wall loosening enzymes, polygalacturonases (PGs). While plant PGs are those responsible for developmental activities like fruit ripening, pollen tube elongation, etc., PGs from various biotic stress factors like insects, fungal and bacterial pathogens aid in invasion by reducing the plant cell wall rigidity. To counteract, plants secrete PGIPs, which inhibit the pectin hydrolyzing activity of PGs from the attacking pests and pathogens. Multiple approaches in diverse crop species have demonstrated PGIP-based protection against pathogens and insect pests. Additionally, effectual interaction between PGs-PGIP is an important aspect for successful utilization of this approach. Molecular strategies leading to improved PG-PGIPs interaction is a highlight to demonstrate the use of PGIPs as an amenable stress mitigation approach. The review focuses on a comprehensive update on phylogeny of PGIPs, natural variation of resistance as well as their emerging translational utility towards mitigation of various biotic stresses.