Trehalose Metabolism 1(OPEN)

to low carbon supply by massive reprogramming of the transcriptome and metabolome. We show here that the carbon starvation-induced ½AU : 6� NAC transcription factor ½AU : 7� ATAF1 from Arabidopsis (Arabidopsis thaliana) plays an important role in this physiological process. We identified TREHALASE1, the only trehalase-encoding gene in Arabidopsis, as a direct downstream target of ATAF1. Overexpression of ATAF1 activates TREHALASE1 expression and leads to reduced trehalose6-phosphate levels and a sugar starvation metabolome. In accordance with changes in expression of starch biosynthesis- and breakdown-related genes, starch levels are generally reduced in ATAF1 overexpressors but elevated in ataf1 knockout plants. At the global transcriptome level, genes affected by ATAF1 are broadly associated with energy and carbon starvation responses. Furthermore, transcriptional responses triggered by ATAF1 largely overlap with expression patterns observed in plants starved for carbon or energy supply. Collectively, our data highlight the existence of a positively acting feedforward loop between ATAF1 expression, which is induced by carbon starvation, and the depletion of cellular carbon/energy pools that is triggered by the transcriptional regulation of downstream gene regulatory networks by ATAF1. Trehalose is a nonreducing disaccharide formed by an a,a-1,1-glucoside bond between two a-Glc units, and it is found in a wide range of organisms (Avonce et al., 2006). Trehalose biosynthesis involves trehalose