Thermal Acclimation in Plants: HSF-Mediated Mechanisms of Thermotolerance in Tomato

• Applicant: Sotirios Fragkostefanakis, Ph.D.
• Subject Area: Plant Genetics and Genomics ; Plant Physiology
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 572267620

Plants are sensitive to temperature elevations, particular those that cause heat stress. Survival and recovery from heat requires the activation of a suite of mechanisms that are dependent on the synthesis of proteins with protective functions for cellular and protein homeostasis, such as heat shock proteins (HSPs). Heat shock factors (HSFs) are the core regulators of heat stress response. In tomato, the master regulator HsfA1a initiates this response, but long-term protection, also known as acquired thermotolerance (ATT) and thermomemory, relies on complex interactions among multiple HSFs, including HsfA2 and HsfA7. This project explores how HSFB2b, a class B HSF, functions as a central regulator of thermomemory and stress adaptation in tomato. Preliminary work using CRISPR mutants and overexpression lines showed that HSFB2b has a dual role: acting as a co-activator with HsfA1b and HsfA9, while repressing HsfA1a-, HsfA2-, and HsfA7-dependent transcription. Intriguingly, HSFB2b affects the expression of key memory genes like APX3 and Hsa32, suggesting it fine-tunes the balance between stress response activation and recovery. The research aims to: Elucidate how HSFB2b controls acquired thermotolerance and thermomemory; Identify new HSF complexes that modulate heat stress response and memory; Investigate gene regulatory networks, chromatin modifications (e.g., H3K4me3, H3K27me3), and protein–protein interactions linked to HSFB2b activity; Determine tissue-specific roles, particularly in reproductive development, to understand how memory contributes to fruit yield protection. The project is expected to deliver critical insights into how plants “remember” heat stress, and how HSFs act as molecular switches to orchestrate stress responses at both transcriptional and chromatin levels. Understanding these mechanisms in tomato, a major crop, will provide critical insights and novel tools and strategies to engineer or breed heat-resilient varieties, ensuring productivity under global warming scenarios.

• DFG Programme: Research Grants