Sugars modulate an unusual mode of control of the cell-wall invertase gene ( Incw 1) through its 3′ untranslated region in a cell suspension culture of maize

Abstract

We show here that a cell-wall invertase encoded by the Incw1 gene is regulated at both the transcriptional and posttranscriptional levels by sugars in a heterotrophic cell suspension culture of maize. The Incw1 gene encoded two transcripts: Incw1-S (small) and Incw1-L (large); the size variation was attributable to different lengths in the 3 untranslated region. Both metabolizable and nonmetabolizable sugars induced Incw1-L RNA apparently by default. However, only the metabolizable sugars, sucrose and D-glucose, were associated with the increased steady-state abundance of Incw1-S RNA, the concomitant increased levels of INCW1 protein and enzyme activity, and the downstream metabolic repression of the sucrose synthase gene, Sh1. Conversely, nonmetabolizable sugars, including the two glucose analogs 3-O-methylglucose and 2-deoxyglucose, induced greater steady-state levels of the Incw1-L RNA, but this increase did not lead to either an increase in the levels of the INCW1 protein͞enzyme activity or the repression of the Sh1 gene. We conclude that sugar sensing and the induction of the Incw1 gene is independent of the hexokinase pathway. More importantly, our results also suggest that the 3 untranslated region of the Incw1 gene acts as a regulatory sensor of carbon starvation and may constitute a link between sink metabolism and cellular translation in plants.The enzyme invertase (EC 3.2.1.26), also known as ␤-fructofuranosidase, is known to catalyze sucrose (suc) cleavage to its monosaccharide constituents, glucose (glc) and fructose, in an irreversible manner. At least two forms of the enzyme, soluble and particulate, are features common to all invertases, and recent molecular analyses indicate that each belongs to two distinct class of small gene families (ref. 1 and references therein). The physiological role of the invertases is believed to be in suc partitioning between source and sink regions of the plant. In general, the vacuolar invertases are believed to be important in the regulation of hexose levels in certain specific tissues and in the use of stored suc in vacuoles. The cell-wall forms (extracellular or secreted) are associated with rapidly growing tissues and have been implicated in phloem unloading and source͞sink regulation (2).Although the experimental evidence is largely correlative in nature, a lot of insight regarding the roles of invertases is now emerging from studies of transgenic or mutant plants. Among several studies on transgenic plants, the most detailed analyses are reported in potato where yeast invertase has been expressed in both the cytosol and apoplast (3). Tissue-specific elevated expression of invertase in both cellular locations leads to substantial reductions in tuber suc content and a corresponding large increase in glc content. More importantly, the apoplastic and cytosolic increases in enzyme activities are associated with different phenotypic responses: an increased tuber size but reduced tuber number in the former and a reversed pattern in the latter. In contrast, w...

The Maize Transcription Factor Myb-Related Protein-1 Is a Key Regulator of the Differentiation of Transfer Cells

“…In addition, sugar sensing also affects gene expression posttranscriptionally by changing mRNA stability, translation, or protein stability (Chan and Yu, 1998;Rook et al, 1998;Cheng et al, 1999;Yanagisawa et al, 2003;Wiese et al, 2004). Interestingly, the regulation of the maize cell wallbound invertase Incw-1 is included among these examples (Cheng et al, 1999). Incw-1 is expressed in maize TCs, and we reported the association between metabolizable sugars and the increase in the steady state abundance of functional Incw-1 RNA.…”

“…Changes in sugar concentration cause induction or repression of gene transcription, providing a mechanism for interaction between sink and source tissues for carbohydrate metabolism (Koch, 1996). In addition, sugar sensing also affects gene expression posttranscriptionally by changing mRNA stability, translation, or protein stability (Chan and Yu, 1998;Rook et al, 1998;Cheng et al, 1999;Yanagisawa et al, 2003;Wiese et al, 2004). Interestingly, the regulation of the maize cell wallbound invertase Incw-1 is included among these examples (Cheng et al, 1999).…”

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

“…Rice suspension cell culture, which is readily amenable to exogenous metabolic manipulations, was used as a model system for these studies. The usefulness of this type of cell culture in such studies is well documented (Graham et al, 1994;Ehness et al, 1997;Cheng et al, 1999;Yu, 1999a). In the present studies, some growth-and stress-related genes upand down-regulated by Suc, respectively, were identified and found to be differentially and coordinately regulated by Suc, and the regulation involves control of both transcription rate and mRNA stability.…”

“…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). The 3Ј-UTR of a cell wall invertase gene (Incw1) recently was shown to be involved in translational control of Incw1 by sugars in cultured maize suspension cells (Cheng et al, 1999).…”

Influence of sugars and hormones on the genes involved in sucrose metabolism in maize endosperms

“…However, ABA and sucrose increased the transcript levels of Incw1, but the induction of ABA combined with sucrose showed no additive effect on the expression of Incw1 (Figure 1). This may be because the Incw1gene encodes 2 distinct transcripts, Incw1-S (small) and Incw1-L (large), which differ in size because the 3ꞌ untranslated region and 2 transcripts induced by sucrose and glucose differ in length (Cheng et al, 1999). The specific effects of ABA on the 2 transcripts are unknown.…”