Plant gene responses to changing carbohydrate status can vary markedly
. Some genes are induced, some are repressed, and others are minimally
affected. As in microorganisms, sugar-sensitive plant genes are part
of an ancient system of cellular adjustment to critical nutrient avail
ability. However, in multicellular plants, sugar-regulated expression
also provides a mechanism for control of resource distribution among t
issues and organs. Carbohydrate depletion upregulates genes for photos
ynthesis, remobilization, and export, while decreasing mRNAs for stora
ge and utilization. Abundant sugar levels exert opposite effects throu
gh a combination of gene repression and induction. Long-term changes i
n metabolic activity, resource partitioning, and plant form result. Se
nsitivity of carbohydrate-responsive gene expression to environmental
and developmental signals further enhances its potential to aid acclim
ation. The review addresses the above from molecular to whole-plant le
vels and considers emerging models for sensing and transducing carbohy
drate signals to responsive genes.