Use of expression analysis to dissect alterations in carbohydrate metabolism in wheat leaves during drought stress

Water deficit in plants causes a reduction in photosynthesis and high demands for osmolyte synthesis. To elucidate regulation of carbohydrate metabolic genes in wheat (Triticum aestivum) leaves during drought stress, we performed a systematic expression study using quantitative RT-PCR and cDNA microarray. These analyses revealed that expression levels of most genes encoding chloroplast enzymes involved in carbon fixation (Calvin cycle) were reduced in the leaves during prolonged drought stress. Transcript levels of highly expressed isoenzymes of hexokinase and fructokinase also decreased. Conversely, genes encoding cytoplasmic and vacuolar enzymes in the pathways leading to glucose, fructose and fructan production were up-regulated in the stressed leaves. Systematic expression analysis of an almost complete set of genes involved in conversion of triose phosphates to hexoses and hexose phosphorylation showed that isoenzymes of many enzymes were differentially regulated during drought stress. Correlation analysis indicated that the drought down-regulated Calvin cycle genes were coordinately regulated. This coordinated down-regulation extended to genes encoding major isoenzymes of chloroplast triosephosphate/phosphate translocator, cytoplasmic fructose-1,6-bisphosphate aldolase and fructose bisphosphatase. Highly correlated expression was also observed between drought up-regulated genes involved in sucrose synthesis and hydrolysis or fructan synthesis. These data dissect coordination in regulation of key enzyme genes involved in carbon fixation and accumulation of hexoses and fructans and provide an insight into molecular mechanisms at the transcript level underlying changes in carbohydrate metabolism in wheat adaptation to drought stress.