The 3′ untranslated region of a rice α-amylase gene functions as a sugar-dependent mRNA stability determinant

Abstract

In plants, sugar feedback regulation provides a mechanism for control of carbohydrate allocation and utilization among tissues and organs. The sugar repression of ␣-amylase gene expression in rice provides an ideal model for studying the mechanism of sugar feedback regulation. We have shown previously that sugar repression of ␣-amylase gene expression in rice suspension cells involves control of both transcription rate and mRNA stability. The ␣-amylase mRNA is significantly more stable in sucrose-starved cells than in sucrose-provided cells. To elucidate the mechanism of sugar-dependent mRNA turnover, we have examined the effect of ␣Amy3 3 untranslated region (UTR) on mRNA stability by functional analyses in transformed rice suspension cells. We found that the entire ␣Amy3 3 UTR and two of its subdomains can independently mediate sugar-dependent repression of reporter mRNA accumulation. Analysis of reporter mRNA half-lives demonstrated that the entire ␣Amy3 3 UTR and the two subdomains each functioned as a sugar-dependent destabilizing determinant in the turnover of mRNA. Nuclear run-on transcription analysis further confirmed that the ␣Amy3 3 UTR and the two subdomains did not affect the transcription rate of promoter. The identification of sequence elements in the ␣-amylase mRNA that dictate the differential stability has very important implications for the study of sugar-dependent mRNA decay mechanisms.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. Expression of enzymes involved in carbohydrate metabolism often is feedback-regulated by excess sugar metabolites. In multicellular plants, feedback repression of gene expression 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 (1-3). Sugar depletion has been shown to enhance expression of a wide variety of genes involved in photosynthesis, reserve mobilization, and carbohydrate-export processes in plants (4); however, the molecular mechanism of sugar repression remains largely unknown.The sugar-dependent repression of ␣-amylase gene expression provides an ideal model for studying the mechanism of sugar feedback regulation in plants. ␣-Amylases are endoamylolytic enzymes that catalyze the hydrolysis of ␣-1,4-linked glucose polymers and play an important role in degradation of starch in higher plants. In rice germinating embryos and cultured suspension cells, expression of ␣-amylase genes is activated by sugar depletion and repressed by sugar provision (3,5,6). An increase in both the transcription rate and mRNA half-life under sucrose depletion contributes to the increase in the steady-state level of ␣-amylase mRNA (7,8). Studies in transgenic rice confirmed that the ␣-amylase gene promoters control sugar-dependent repression of reporter gene expression (9-11).Most studies of sugar...

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Arabidopsis Sucrose Transporter AtSUC9. High-Affinity Transport Activity, Intragenic Control of Expression, and Early Flowering Mutant Phenotype

“…The results confirm AtSUC9 expression in flowers and siliques, suggesting that there are additional regulatory elements outside the 5# region. Regulatory elements outside the 5# region are well documented (Taylor, 1997); for example, AGAMOUS (Deyholos and Sieburth, 2000), rice (Oryza sativa) a-amylase (Chan and Yu, 1998), and a-fetoprotein (Scohy et al, 2000) are plant genes with intragenic regulatory elements. Additionally, AtSUC1 also shows differential expression patterns when comparing whole-geneTGUS to promoterTGUS.…”

The Arabidopsis Tandem Zinc Finger Protein AtTZF1 Traffics between the Nucleus and Cytoplasmic Foci and Binds Both DNA and RNA

“…A plausible mechanism for AtTZF1 to control gene expression is via posttranscriptional regulation, an area that has not been addressed widely in plant sugar signaling. For example, the mRNA halflife of rice a-amylase gene is affected by sugar via destabilization signal sequences at the 3# UTR (Chan and Yu, 1998). Furthermore, the 3# UTR of the maize cell wall invertase gene Incw1 is likely to affect sugardependent mRNA metabolism and translation (Cheng et al, 1999).…”