Trehalose or Not-Trehalose: The Question of Direct vs. Indirect Transcriptional Responses to the sugar trehalose-6-phosphate

In terrestrial ecosystems, plants act as primary producers by sequestering carbon from CO2 and 10 incorporating it into the soluble sugar form.These sugars are transported out of the leaves, 11 usually in the form of sucrose, and into sink organs such as roots and fruits.The distribution of 12 sugars within the plant at any given time is non-uniform, and plants must continually monitor 13 their sugar levels to control carbohydrate homeostasis and other signaling processes.In addition 14 to directly sensing the primary soluble sugar, it has been proposed that plants can also perceive 15 trehalose-6-phosphate (Tre6P) as a signal of sugar availability.Tre6P is the intermediate 16 molecule in the synthesis of the sugar trehalose.Trehalose metabolism is facilitated by two 17 enzymes: trehalose-6-phosphate synthase (TPS) and trehalose-phosphate phosphatase (TPP).In 18 the first step, TPS catalyzes the synthesis of Tre6P from uridine diphosphate (UDP)-glucose and 19 glucose-6-phosphate.TPP then dephosphorylates Tre6P to produce trehalose (Figure 1).20 In addition to its role in sugar sensing, Tre6P controls developmental processes such as 21 flowering time, inflorescence architecture, and shoot branching (Wahl et al., 2013, Satoh-22 Nagasawa et al., 2006, Fichtner et al., 2021, reviewed in Fichtner and Lunn, 2021).While it is 23 understood that Tre6P can rapidly induce changes in gene expression, the mechanisms of Tre6P 24 perception and downstream signaling are still elusive.25 In this study, Avidan et al., (2024) used an inducible TPS enzyme to identify the direct gene-26 expression targets of Tre6P.The authors used an ethanol-inducible version 27 of the TPS enzyme from E. coli (iTPS) transformed into Arabidopsis to analyze the short-term (4-6 hours) 28 transcriptional responses to Tre6P.Previous studies have been limited by genetic interventions 29 that altered TPS and TPP expression causing constitutive changes in both Tre6P and sucrose