IMPROVING REPRODUCTIVE THERMOTOLERANCE THROUGH MAINTENANCE OF ROS HOMEOSTASIS

Plant reproduction is impaired at elevated temperatures, reducing seed and fruit production and leading to devastating crop losses. High temperature stress elevates reactive oxygen species (ROS) to damaging levels in pollen. Little is known about how this temperature-induced ROS is synthesized and how thermotolerant Solanum lycopersicum (tomato) cultivars maintain pollen viability and tube growth. We have found that a tomato mutant with impaired flavonol antioxidant synthesis has elevated ROS and pollen grains and tubes that are hypersensitive to high temperature, while a plant transformed with a transgene leading to overproduction of flavonols is thermotolerant. Thermotolerant cultivars have pollen tube growth and ROS levels that do not change at elevated temperatures. These findings suggest plant defense against high temperature includes synthesis of specialized, antioxidant metabolites that maintain ROS homeostasis.This project will identify the mechanisms by which pollen of thermosensitive varieties have elevated temperature-induced ROS and why thermotolerant cultivars maintain their ROS homeostasis. We will test the hypothesis that pollen of these thermotolerant cultivars have reproductive success at high temperature due to reduced ROS biosynthesis and/or elevated synthesis of flavonols and other antioxidant systems. We will apply the gained knowledge to engineer plants with enhanced thermotolerance, using flavonol antioxidants as a target to be overproduced and the heat-induced ROS synthesizing machinery as targets for deletion in a heat stress- and pollen-specific manner. The proposed experiments will provide insights into the role of ROS homeostasis in tomato reproduction under adverse climate conditions with the goal of engineering plants to produce thermotolerant pollen. This project will explore the mechanisms by which the balance between ROS levels and their mitigation by flavonols (and other antioxidant metabolites and proteins) modulate pollen function at high temperatures in thermosensitive and thermotolerant cultivars. The planned experiments will provide insights into the role of ROS and antioxidants in plant reproduction under adverse climate conditions with the goal of engineering thermotolerant tomato pollen using heat-stress induced and pollen targeted approaches.This project has 3 specific aims:Aim 1: Identify spatiotemporal ROS accumulation in pollen during heat stress and define the biosynthetic machinery that controls high temperature-induced ROS synthesis.Aim 2: Determine if elevated temperature induces biosynthesis of flavonols and/or other antioxidants to maintain ROS homeostasis in tomato pollenAim 3: Perform precision metabolic engineering to improve reproductive thermotolerance in tomato by increasing flavonols in male reproductive structures