Genotypic differences in water soluble carbohydrate metabolism in stem

Water soluble carbohydrates (WSC, composed of mainly fructans, sucrose, glucose and fructose) deposited in wheat stems are important carbon sources for grain filling. Variation in stem WSC concentrations among wheat genotypes is one of the genetic factors influencing grain weight and yield under water-limited environments. Here, we describe the molecular dissection of carbohydrate metabolism in stems, at the WSC accumulation phase, of recombinant inbred SB (Seri/Babax) lines of Triticum aestivum differing in stem WSC concentrations. Affymetrix GeneChip analysis of carbohydrate metabolic enzymes revealed that the mRNA levels of two fructan synthetic enzyme families (sucrose:sucrose 1-fructosyltransferase and sucrose:fructan 6-fructosyltransferase) in the stem were positively correlated with stem WSC and fructan concentrations, while the mRNA levels of enzyme families involved in sucrose hydrolysis (sucrose synthase and soluble acid invertase) were inversely correlated with WSC concentrations. Differential regulation of the mRNA levels of these sucrose hydrolytic enzymes in SB lines resulted in genotypic differences in these enzyme activities. Down-regulation of sucrose synthase and soluble acid invertase in high WSC lines was accompanied by significant decreases in the mRNA levels of enzyme families related to sugar catabolic pathways (fructokinase and mitochondrion pyruvate dehydrogenase complex) and enzyme families involved in diverting UDP-glucose to cell wall synthesis (UDP-glucose 6-dehydrogenase, UDP-glucuronate decarboxylase and cellulose synthase), resulting in a reduction in cell wall polysaccharide contents (mainly hemicellulose) in the stem of high WSC lines. These data suggest that differential carbon partitioning in the wheat stem is one mechanism that contributes to genotypic variation in WSC accumulation.

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Xue GP, McIntyre CL, Jenkins CL, Glassop D, van Herwaarden AF, Shorter R