Osmotin

Osmotin is a plant protein belonging to the pathogenesis-related PR-5 family, closely related to thaumatin-like proteins. It was first described in Nicotiana tabacum (tobacco) and is widely studied for its roles in osmotic stress responses and plant defense.

Biochemical properties: Osmotin is a secreted glycoprotein of about 27 to 32 kilodaltons in its mature form and contains multiple disulfide bonds typical of PR-5 proteins, contributing to stability in the extracellular space. The protein is secreted into the apoplast, where it can accumulate in response to environmental cues. Osmotin-like proteins are found across many plant species, including tomato, potato, and various fruit crops.

Function and regulation: Osmotin expression is induced by osmotic stress from high salinity and drought, as well as by cold, abscisic acid, and pathogen attack. In plants, osmotin is associated with osmotic protection and cellular defense under stress and has antifungal activity in vitro, with proposed mechanisms involving interaction with fungal membrane components such as sphingolipids and disruption of membrane integrity. In transgenic studies, overexpression of osmotin or osmotin-like proteins often improves tolerance to salt, drought, or cold, and can enhance resistance to certain pathogens.

Applications and taxonomy: Osmotin is part of the PR-5 protein family, which also includes thaumatin-like proteins. It is studied as a model for plant abiotic and biotic stress responses and has potential applications in biotechnology to increase crop resilience through genetic approaches.