TOLs, modulators during abiotic stress responses

Climate change and its impact on the adaptive capacity of plants is a highly topical area of research. Plants, as sessile organisms, cannot simply move away from an unfavorable environment and have therefore evolved intricate mechanisms to rapidly and precisely respond and adapt to their environment. This project addresses the cellular response of higher plants to drought stress, which is coordinated by the hormone abscisic acid (ABA). To modulate and fine-tune the ABA signaling pathway, key proteins are down-regulated by degradation. We intend to functionally characterize the involvement of the TOL (TOM1-like) protein family in the degradation of these key components, as a tol mutant plant line is more drought resistant than a wild-type plant line of the same ecotype it resembles under standard conditions. TOL proteins initiate the transport of plasma membrane-associated proteins, which are marked for degradation by ubiquitination, to the vacuole. Thus, in this project, a strong focus is placed on E3 ligases that catalyze the transfer of the protein ubiquitin to another protein. In addition, to link the function of TOL genes to the regulation of ABA responses, the genetic interaction of TOLs with ABA biosynthesis and signaling mutants will be investigated. Furthermore, subunits of the transport complex involved in ABA receptor degradation will be examined for interaction with TOLs to reveal functional linkages. ABA transporters and receptors as well as TOL reporter lines will be investigated with respect to their localization and abundance in different tol mutant backgrounds under drought stress. Thus, this project will elucidate how TOL proteins function in modulating the ABA pathway in plants. In summary, this project will contribute to the understanding of how TOLs, in addition to their general role in the endosomal degradation pathway, play a more differentiated role in the ABA signaling pathway that regulates drought stress. Fine-tuning of signaling pathways allows plants to adapt to their environment to respond resilliently to a changing environment.

How plants fine-tune their drought response As climate change increases the frequency and severity of droughts, understanding how plants cope with water scarcity has become more important than ever. Plants rely on a natural stress hormone called abscisic acid (ABA) to survive dry conditions by regulating water use and closing pores in their leaves to prevent water loss. For this system to work properly, ABA signaling must be tightly balanced, with signals turned on when needed and switched off again at the right moment. Our research uncovers a key mechanism that plants use to fine-tune this drought response. We show that a group of proteins known as TOM1-LIKE (TOL) proteins play a central role in regulating the stability and turnover of crucial ABA signaling and transport components. These TOL proteins act as part of the cell's internal recycling system, guiding specific ABA-related proteins to a cellular waste compartment where they are broken down once they are no longer needed. By studying plants lacking several TOL proteins, we discovered that these plants are unusually sensitive to ABA and significantly more tolerant to drought, yet they grow and develop normally under standard conditions. This makes the TOL proteins especially interesting targets for improving crop performance, as manipulating them could enhance drought tolerance without negative side effects on plant growth. Overall, this work reveals how plants use targeted protein degradation to precisely control stress hormone signaling. Understanding these processes brings us a step closer to developing crops that are better equipped to withstand the challenges of a changing climate.