Protease Inhibitors and Stress Tolerance

Plant protease inhibitors (PIs) are extensively studied for their role in defense against pests and pathogens due to their ability to inhibit specific proteases of the intruder. All classes of PIs were found to play important roles in innate host defense mechanisms and are used to develop transgenic plants resistant to pests and pathogens. Recent reports suggest that they have a role in modulating abiotic stress tolerance also. The induction of PIs was observed in response to not only biotic but also abiotic cues suggesting their possible role in abiotic stress responses and in modulating tolerance to various stresses. During biotic stress, pathogen invasion or damage due to herbivory, induces SA/JA-mediated signalling pathways to combat the attack. Abiotic stress induces injury and different conditions like osmotic stress, oxidative stress etc. as long as the causative factor exists in the milieu. Unlike in the biotic stresses, the causative agent in abiotic stress cannot be countered by the plant. Hence, the abiotic stress has to be tolerated by the plant nullifying all its related damages mostly by adjustment through ABA-dependent, and sometimes through an independent pathway. The overexpression of PIs has been shown to enhance abiotic stress tolerance in the transgenic plants suggesting that their role is multidimensional. In this review, we focus on the possible role of PIs in plant growth, and biotic and abiotic stress tolerance. _____________________________________________________________________________________________________________