Proteolysis activities in creeping bentgrass leaves subjected to heat stress

Enhanced protein degradation, typically conducted by the coordinated action of proteases and the ubiquitin-proteasome system (UPS), is a common response to heat stress. It works by removing nonfunctional or damaged proteins to maintain normal cell function and to allow for the remobilization of nutrients, enabling plants to respond rapidly to environmental perturbation. Despite its crucial role, there has been limited research addressing proteolysis activities from both proteases and the UPS in grasses exposed to heat stress. This project aims to quantify activities of proteases and the UPS in different lines of creeping bentgrass (Agrostis stolonifera L.), a cool-season turfgrass that's prized for its functional and aesthetic qualities, and detect changes in expression levels of known proteases and the UPS genes. Previously identified heat-tolerant and -sensitive creeping bentgrass lines were selected for this study. They were exposed to either control (20/15°C day/night) or heat stress (38/33°C day/night) treatments for 35 d. Protein degradation was enhanced under heat as demonstrated by significant increases in protease activity and the UPS activity over time. A more heat-tolerant line, S11 729-10, maintained lower activities of both protease and the UPS, contributing to its higher protein contents, and thereby greater thermotolerance. Additionally, gene expression was variable across lines, with heat sensitive Crenshaw having lower expression levels as heat stress progressed. This is the first time that the roles of protease activity and the UPS activity in heat stress were simultaneously analyzed in a perennial grass species. Such information will broaden the understanding of how protein degradation is regulated in response to heat stress, providing a deeper insight into thermotolerance mechanisms in creeping bentgrass.