ACTIVATOR of Spomin::LUC1/WRINKLED1 of Arabidopsis thaliana Transactivates Sugar-inducible Promoters

Abstract

We isolated an enhancer activation-tagged mutant of Arabidopsis thaliana line sGsL carrying the luciferase (LUC) gene under control of a short sugar-inducible promoter derived from a sweet potato sporamin gene (Spomin) that showed high level expression of LUC under non-inducing conditions. The activator of Spomin::LUC1 (ASML1) gene located downstream of the enhancer encoded an APETALA2 (AP2)-type AP2 domain protein, and this gene was shown recently to be responsible for the wrinkled1 mutation which causes defective accumulation of seed storage oil. Overexpression of ASML1 cDNA in sGsL plants resulted in enhanced expression of not only the LUC reporter but also endogenous sugar-inducible genes including Atbeta-Amy encoding beta-amylase. Transient co-expression of 35S::ASML1 with Spomin::LUC or Atbeta-Amy::LUC reporters in protoplasts resulted in an approximately 10-fold transactivation of LUC expression. This transactivation was lost when the C-terminal acidic region of ASML1 was deleted. Expression of ASML1 was high in reproductive organs, and ASML1 mRNA showed transient accumulation in leaves after treatment with 6% sucrose, whereas it did not respond to abscisic acid. These results suggest that ASML1/WRI1 is a transcriptional activator involved in the activation of a subset of sugar-responsive genes and the control of carbon flow from sucrose import to oil accumulation in developing seeds.

The SUGAR-DEPENDENT1 Lipase Limits Triacylglycerol Accumulation in Vegetative Tissues of Arabidopsis

“…Increased sugar concentration triggers wide-scale changes in gene expression and enzyme activities in Arabidopsis, many of which are associated with primary metabolism (Bläsing et al, 2005;Osuna et al, 2007). For example, there is evidence that both WRI1 and DGAT1 are induced by sugar (Lu et al, 2003;Masaki et al, 2005).…”

“…Importantly, we observed that SDP1 disruption does boost TAG accumulation in leaves when exogenous sugar is applied or when DGAT1 and WRI1 are overexpressed. In both cases, TAG synthesis is artificially stimulated (Bouvier-Navé et al, 2000;Lu et al, 2003;Cernac and Benning, 2004;Masaki et al, 2005); therefore, SDP1-mediated TAG turnover must become more active under these nonphysiological conditions. Lipid metabolism in Arabidopsis roots and stems has received rather less attention than in leaves (LiBeisson et al, 2013).…”

Deciphering gene regulatory networks that control seed development and maturation in Arabidopsis

“…At the transcriptional level, LEC1 may participate in regulation of WRI1 expression (Casson and Lindsey, 2006). Likewise, sucrose may play a role in triggering the induction of WRI1, as well as of LEC2, FUS3 and ABI3 (Masaki et al, 2005;Tsukagoshi et al, 2007).…”

Transcription factors for sugar-inducible genes

“…The Cterminal part of ASML1 is enriched with acidic amino acids, and co-expression of ASML1-DC with deletions in the C-terminal acidic region failed to show activation of Spo min ::LUC. These results suggest that ASML1 probably acts directly to Spo min and Atb-Amy promoters as a transcriptional activator and the C-terminal acidic region of ASML1 acts as an activation domain (Masaki et al 2005a). The DNA-binding properties and the binding site sequence-specificity of ASML1 are currently under analysis.…”

“…In this mutant, the enhancer T-DNA was inserted in the lower arm of chromosome 3 near APETALA3, and a gene designated ASML1 for Activator of Spo min ::LUC1 located between the enhancer and APETALA3 was significantly elevated compared to the sGsL plants (Masaki et al 2005a). The sGsL plants that overexpress ASML1 cDNA under the CaMV 35S promoter mimicked phenotypes of the original mutant.…”