Linked gene networks involved in nitrogen and carbon metabolism and levels of water-soluble carbohydrate accumulation in wheat stems

High levels of water-soluble carbohydrates (WSC) provide an important source of stored assimilate for grain filling in wheat. To better understand the interaction between carbohydrate metabolism and other metabolic processes associated with the WSC trait, a genome-wide expression analysis was performed using eight field-grown lines from the high and low phenotypic tails of a wheat population segregating for WSC and the Affymetrix wheat genome array. The 259 differentially expressed probe sets could be assigned to 26 functional category bins, as defined using MapMan software. There were major differences in the categories to which the differentially expressed probe sets were assigned; for example, probe sets upregulated in high relative to low WSC lines were assigned to category bins such as amino acid metabolism, protein degradation and transport and to be involved in starch synthesis-related processes (carbohydrate metabolism bin), whereas downregulated probe sets were assigned to cell wall-related bins, amino acid synthesis and stress and were involved in sucrose breakdown. Using the set of differentially expressed genes as input, chemical-protein network analyses demonstrated a linkage between starch and N metabolism via pyridoxal phosphate. Twelve C and N metabolism-related genes were selected for analysis of their expression response to varying N and water treatments in the field in the four high and four low WSC progeny lines; the two nitrogen/amino acid metabolism genes demonstrated a consistent negative association between their level of expression and level of WSC. Our results suggest that the assimilation of nitrogen into amino acids is an important factor that influences the levels of WSC in the stems of field-grown wheat