Secondary Metabolites Mediated Reproductive Tolerance Under Heat Stress in Plants

Supra-optimal temperature adversely affects plant growth and development. Among different growth phases, the reproductive stage of plants is highly sensitive to high temperature stress. The heat tolerance of plants is reliant on a complex interplay of various factors, including the activation of heat stress responses, downstream signaling pathways, and biosynthesis of plant hormones. This intricate network of mechanisms results in the production of several secondary metabolites, which play a crucial role in enhancing the plant's ability to cope with high temperature stress. Many of these secondary metabolites are crucial for the reproductive performance of plants, as they are involved in the attraction of pollinators, pollen germination, pollen tube growth, pollen viability, pollen fertility, and fertilization. Reproductive tissues of plants are highly vulnerable to heat stress, but increased biosynthesis of secondary metabolites (flavonoids, polyamines, glutathione, etc.) induces reproductive thermotolerance through reactive oxygen species homeostasis, protecting the cellular membranes, improving pollen fertility, reducing anther abortion, regulating cellular signaling and activation of genes/transcription factors associated with metabolic pathway network. The identification and engineering of some genes controlling the secondary metabolic pathways network have proved effective in inducing terminal heat stress tolerance in transgenic plants. This review highlights the effect of heat stress on plant secondary metabolism and the role of different plant secondary metabolites in contributing to heat stress tolerance in reproductive tissues. The engineering of genes involved in plant secondary metabolic pathway and their effect on heat stress tolerance has also been discussed.