Inhibition of SNF1-related protein kinasel activity and regulation of metabolic pathways by trehalose-6-phosphate^1[w][OA]

Trehalose-6-phosphate (T6P) is a proposed signaling molecule in plants, yet how it signals was not clear. Here, we provide evidence that T6P functions as an inhibitor of SNFl-related protein kinasel (SnRK1; AKIN10/AKIN11) of the SNFl-related group of protein kinases. T6P, but not other sugars and sugar phosphates, inhibited SnRKl in Arabidopsis (Arabidopsis thaliana) seedling extracts strongly (50%) at low concentrations (1-20 μM). Inhibition was noncompetitive with respect to ATP. In immunoprecipitation studies using antibodies to AKIN10 and AKIN11, SnRKl catalytic activity and T6P inhibition were physically separable, with T6P inhibition of SnRKl dependent on an intermediary factor. In subsequent analysis, T6P inhibited SnRKl in extracts of all tissues analyzed except those of mature leaves, which did not contain the intermediary factor. To assess the impact of T6P inhibition of SnRKl in vivo, gene expression was determined in seedlings expressing Escherichia coli otsA encoding T6P synthase to elevate T6P or otsB encoding T6P phosphatase to decrease T6P SnRKl target genes showed opposite regulation, consistent with the regulation of SnRKl by T6P in vivo. Analysis of microarray data showed up-regulation by T6P of genes involved in biosynthetic reactions, such as genes for amino acid, protein, and nucleotide synthesis, the tricarboxylic acid cycle, and mitochondrial electron transport, which are normally down-regulated by SnRKl. In contrast, genes involved in photosynthesis and degradation processes, which are normally up-regulated by SnRKl, were down-regulated by T6P These experiments provide strong evidence that T6P inhibits SnRKl to activate biosynthetic processes in growing tissues.