Roles of cell-wall invertases and monosaccharide transporters in the growth and development of Arabidopsis
Sherson, SM and Alford, HL and Forbes, SM and Wallace, G and Smith, SM, Roles of cell-wall invertases and monosaccharide transporters in the growth and development of Arabidopsis, Journal of Experimental Botany, 54, (382) pp. 525-531. ISSN 0022-0957 (2003) [Refereed Article]
The hydrolysis of sucrose by cell‐wall invertases (cwINV) and the subsequent import of hexoses into target cells appears to
be crucial for appropriate metabolism, growth and differentiation in plants. Hexose uptake from the apoplast is catalysed
by monosaccharide/H+ symporters (Sugar Transport Proteins or STPs), which have the potential to sense sugars. Import of extracellular hexoses
may generate signals to orchestrate cellular activities, or simply feed metabolic pathways distinct from those fed by sucrose.
It is predicted that Arabidopsis has six cwINV genes and at least 14 STP genes. These genes show different spatial and temporal patterns of expression, and several knock‐out mutants have been isolated
for analysis. AtSTP1 transports glucose, galactose, xylose, and mannose, but not fructose. It accounts for the majority of
the AtSTP activity in vegetative tissues and its activity is markedly repressed by treatment with exogenous sugars. These
observations are consistent with a role in the retrieval of cell‐wall‐derived sugars, for example, during carbohydrate limitation
or cell expansion. The AtSTP1 gene is also expressed in developing seeds, where it might be responsible for the uptake of glucose derived from imported
sucrose. The large number of AtcwINV and AtSTP genes, together with complex patterns of expression for each, and the possibility that each protein may have more than one
physiological function, provides the plant with the potential for a multiplicity of patterns of monosaccharide utilization
to direct growth and differentiation or to respond flexibly to changing environmental conditions.