Activation tagging of a gene for a protein with novel class of CCT-domain activates expression of a subset of sugar-inducible genes in Arabidopsis thaliana

Abstract

In the current studies, we examined sugar-inducible gene expression using the Arabidopsis thaliana line sGsL, which carries luciferase (LUC) and β-glucuronidase (GUS) reporter genes under the control of a 210-bp promoter derived from the sweet potato sporamin gene (Spomin). We isolated an enhancer activation-tagged mutant of this line that showed high-level expression of LUC and GUS under non-inducing low-sugar conditions. The Activator of Spomin::LUC2 (ASML2) gene located close to the enhancer encodes a protein belonging to a previously uncharacterized class of CCT (CONSTANS, CONSTANS-like, TOC1) domain proteins. Overexpression of ASML2 cDNA in the sGsL line resulted in enhanced expression of not only LUC and GUS reporters but also several endogenous sugar-inducible genes, including Atβ-Amy, ApL3, and VSP2. Transient co-expression of 35S::ASML2 with the Spomin::LUC or Atβ-Amy.:LUC reporter in protoplasts resulted in an approximately 2.4 or 5.6-fold transactivation of LUC expression, respectively. Expression of ASML2 was high in reproductive organs, and expression in seedlings was slightly enhanced by sugars, but not by abscisic acid. These results suggest that ASML2 functions as a transcriptional activator and regulates the expression of at least a subset of sugar-inducible genes. © 2005 Blackwell Publishing Ltd.