Elucidating the functional role of trehalose 6-phosphate in thermotolerance in Arabidopsis thaliana

• Applicant: Dr. Daniel Maag
• Subject Area: Plant Physiology
• Term: since 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 416992417

Temperature is a key determinant of plant growth and performance. Accordingly, extreme temperatures can exert detrimental effects on a plant’s reproductive success, or in the case of crop plants, yield. At the cellular level, high temperatures cause a decline in photosynthetic rates that is accompanied by enhanced photorespiration resulting in an overall reduction of carbon assimilation. At the same time, plant heat stress resistance depends on a massive reconfiguration of the proteome as part of the genetically encoded heat shock response (HSR), imposing high energetic and metabolic costs. Therefore, a tight coordination between the HSR and the plant’s energy status is required, especially under the energy-limiting conditions that are associated with long-term heat. In agreement with this, we recently discovered that TREHALOSE-6-PHOSPHATE SYNTHASE 1 (TPS1) affects long-term thermotolerance in Arabidopsis thaliana, likely via the action of its catalytic product trehalose 6-phosphate (T6P) as a proposed low-level regulator of sucrose homeostasis. Accordingly, complementation of the tps1-1 null mutant with functionally distinct TPS1 isoforms differentially affected carbohydrate metabolism under more severe heat stress. While higher TPS1 activity was associated with reduced endogenous sucrose levels during heat stress and a decrease in thermotolerance, disruption of trehalose 6-phosphate signalling resulted in higher accumulation of transitory starch and sucrose and was associated with enhanced heat resistance. In addition, T6P levels declined rapidly in heat-stressed wild-type seedlings. However, it is unclear how T6P impinges on plant thermotolerance exactly. We therefore propose to study the role of T6P in thermotolerance in more detail. Based on our preliminary work we hypothesise that heat-dependent changes in T6P levels generate a rapid signal that triggers the transient remobilisation of transitory starch reserves during heat stress to provide carbon and energy for the onset of the HSR. To test this hypothesis, we will first characterise the kinetics of heat-dependent metabolic changes including T6P, soluble sugars and starch at high temporal resolution. Using available mutant lines, we will then determine the functional relevance of heat-induced enzymatic degradation of T6P and remobilisation of transitory starch for seedling thermotolerance. In parallel, we will generate transgenic lines allowing for the inducible modification of in planta T6P levels. These lines will then be used to assess the transcriptional basis of the observed T6P-dependent differences in thermotolerance. Furthermore, we aim at the identification and initial characterisation of transcriptional regulators that are involved in the mediation of the T6P-dependent response based on the observed transcriptomic changes. Taken together, the proposed project will enhance our understanding of how plants coordinate abiotic stress responses with their prevailing energy status.

• DFG Programme: Research Grants