Sugars modulate an unusual mode of control of the cell-wall invertase gene(Incw1) through its 3 ' untranslated region in a cell suspension culture of maize

We show here that a cell-wall invertase encoded by the Incw1 gene is regula ted at both the transcriptional and posttranscriptional levels by sugars in a heterotrophic cell suspension culture of maize. The Incw1 gene encoded t wo transcripts: Incw1-S (small) and Incw1-L (large); the size variation was attributable to different lengths in the 3' untranslated region, Both meta bolizable and nonmetabolizable sugars induced Incw1-L RNA apparently by def ault. However, only the metabolizable sugars, sucrose and D-glucose, were a ssociated with the increased steady-state abundance of Incw1-S RNA, the con comitant increased levels of INCW1 protein and enzyme activity, and the dow nstream metabolic repression of the sucrose synthase gene, Sh1, Conversely, nonmetabolizable sugars, including the two glucose analogs 3-O-methylgluco se and 2-deoxy-glucose, 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 protein/enzyme activity or the repression of the Sh1 gene. We con clude 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 o f carbon starvation and may constitute a link between sink metabolism and c ellular translation in plants.