Identification of genes that are up‐regulated in concert during sugar depletion in Arabidopsis

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Abstract
In order to identify sugar‐responsive genes, Arabidopsis cDNA macro‐arrays were hybridized with probes prepared from seedlings cultured in the presence or absence of sucrose. Initial screening identified 36 cDNAs that were affected, among which 11 were finally selected as being up‐regulated under sugar‐depleted conditions. Eight of them were novel in terms of known sugar responses. Based on the properties of encoded proteins, they were classified into three groups involved in amino acid metabolism, carbohydrate metabolism and unidentified nature. Subsequently, correlations between their expression profiles and sugar levels were analysed using intact plants. When detached leaves were subjected to sucrose depletion for 12 h, a marked decrease in glucose and sucrose occurred, and concomitantly all 11 genes were up‐regulated. However, their transcripts rapidly diminished within 7 h when samples were re‐supplied with sucrose. A similar pattern of up‐ and down‐regulation was observed upon dark treatment of whole plants but not during natural senescence of mature leaves. Inhibition analyses with glucose analogues indicated that eight of these genes might be associated with the hexokinase signalling pathway. The present observations suggest that plants activate a set of genes involved in recycling of materials during sugar depletion, and that these genes are simultaneously and concertedly regulated despite functional diversity.