Sugar Response Sequence in the Promoter of a Rice α-Amylase Gene Serves as a Transcriptional Enhancer

Abstract

Expression of ␣-amylase genes in both rice suspension cells and germinating embryos is repressed by sugars and the mechanism involves transcriptional regulation. The promoter of a rice ␣-amylase gene ␣Amy3 was analyzed by both loss-and gain-of-function studies and the major sugar response sequence (SRS) was located between 186 and 82 base pairs upstream of the transcription start site. The SRS conferred sugar responsiveness to a minimal promoter in an orientation-independent manner. It also converted a sugar-insensitive rice actin gene promoter into a sugar-sensitive promoter in a dosedependent manner. Linker-scan mutation studies identified three essential motifs: the GC box, the G box, and the TATCCA element, within the SRS. Sequences containing either the GC box plus G box or the TATCCA element each mediated sugar response, however, they acted synergistically to give a high level glucose starvation-induced expression. Nuclear proteins from rice suspension cells binding to the TATCCA element in a sequence-specific and sugar-dependent manner were identified. The TATCCA element is also an important component of the gibberellin response complex of the ␣-amylase genes in germinating cereal grains, suggesting that the regulation of ␣-amylase gene expression by sugar and hormone signals may share common regulatory machinery.Sugar repression of gene expression is a fundamental and ubiquitous regulatory system for adjusting to changes in nutrient availability in both prokaryotic and eukaryotic cells. In microorganisms, glucose or other rapidly metabolizable carbon sources repress the expression of genes that code for enzymes related to the metabolism of other carbon sources. Our understanding of the mechanisms of sugar repression has been based largely on studies of microorganisms. In the case of Escherichia coli, a model to explain at the molecular level, the mechanism of sugar repression has been determined (1, 2). The mechanism of glucose repression in yeast is more complicated and is less understood than it is in E. coli (3-5). Studies using Saccharomyces cerevisiae mutants have revealed many of the components involved in the response to carbon catabolite repression (5), but it is still unclear how all of these components interact to regulate transcription. A universal signaling pathway which leads to the regulation of all glucose-repressible genes has yet to be determined.As in microorganisms, sugar repression of gene expression also allows plant cells to cope effectively with changes in the carbon sources present in their environment. However, in multicellular plants, feedback repression by excess sugars provides an additional mechanism for maintaining an economical balance between supply (source) and demand (sink) for carbohydrate allocation and utilization among tissues and organs (6 -8). Despite the fact that sugar repression of gene expression is likely a central control mechanism mediating energy homeostasis and carbohydrate distribution in plants, the molecular mechanism of sugar feedback regulation remain...

Sugar Coordinately and Differentially Regulates Growth- and Stress-Related Gene Expression via a Complex Signal Transduction Network and Multiple Control Mechanisms

“…Specific cis-regulatory elements in the promoters or mRNAs are probably shared by these sugar-regulated genes. The SRC of ␣Amy3 promoter contains a TATCCA element that has been shown to serve as an enhancer for sugar starvation-induced expression (Lu et al, 1998). The TATCCA element along with its variants are present at a proximity upstream of the transcription start sites of 18 ␣-amylase genes isolated from various plant species (Yu, 1999b) and other sugar-repressible genes, e.g.…”

“…Most studies on the mechanisms of sugar activation and sugar repression in plants have emphasized regulation at the transcriptional level (Sheen, 1990;Chan et al, 1994;Graham et al, 1994;Lu et al, 1998). However, sugar repression of ␣-amylase gene expression involves control of both transcription and mRNA stability (Sheu et al, 1994(Sheu et al, , 1996.…”

“…A sugar response complex (SRC) in the promoter region of a Suc deprivation highly inducible rice ␣-amylase gene, ␣Amy3, has been identified. This SRC contains three essential motifs for a high level of sugar starvationinduced gene expression in rice cells (Lu et al, 1998). Studies on ␣Amy3 mRNA have also identified essential sequences in its 3Ј-untranslated region (3Ј-UTR) that control sugar-dependent mRNA stability Yu, 1998a, 1998b).…”

Tomato RAV Transcription Factor Is a Pivotal Modulator Involved in the AP2/EREBP-Mediated Defense Pathway

“…The transfected cells were incubated for 20 h at 22°C under light, harvested by centrifugation at 100g for 2 min, and then lysed in lysis buffer (Promega). Luciferase activity was measured by use of a luciferase assay kit (Promega) according to the manufacturer's instructions, and GUS activity was determined (Lu et al, 1998).…”

The SnRK1A Protein Kinase Plays a Key Role in Sugar Signaling during Germination and Seedling Growth of Rice

“…aAmy3 and aAmy8 constitute two major rice a-amylases expressed under sugar-depleted conditions and are important for the catabolism of starch as a carbon source when sugar levels become too low to sustain respiration and growth in rice suspension cells and germinating embryos Yu, 1999;Chen et al, 2006). Sugar repression of a-amylase gene expression involves the control of transcription rate and mRNA stability (Chan et al, 1994;Sheu et al, 1994Sheu et al, , 1996Yu, 1998a, 1998b), and common regulatory elements in aAmy3 and aAmy8 sugar response complexes (SRCs) have been identified (Hwang et al, 1998;Lu et al, 1998;Toyofuku et al, 1998;Chen et al, 2006). The 100-bp aAmy3 SRC contains three essential motifs, the GC box, the G box, and the TA box, for high-level promoter activity under sugar-depleted conditions (Lu et al, 1998).…”