LongSAGE analysis of the early response to cold stress in Arabidopsis leaf

The initial events involved in signal transduction generated by cold exposure are poorly known in plants. We were interested in the characterization of early response to cold stress in Arabidopsis leaves. So we examined plants exposed to 0 degrees C for 1 h. Using LongSAGE at the level of transcription, a total of 27,612 tags, including 11,089 unique tags were sequenced and analyzed. By adopting LongSAGE methods, the ambiguity of tag identification was reduced by about 10%. Only 46% of identified tags in the 1-h cold-stressed plants matched existing Arabidopsis UniGene entries. A comparison of the tags derived from the cold-treated leaves with those identified in the non-treated leaves revealed 315 differentially expressed genes (P < 0.01). Functional classification of expressed genes during the early cold response indicated that genes were involved in light harvesting, the Calvin cycle, and photorespiration were expressed at relatively low levels compared to their presence in non-cold-stressed plants. On other hand, genes involved in mitochondrial electron transport and ATP synthesis showed an increased expression. Some orphan LongSAGE tags uniquely matched pri-miRNA, suggesting the existence of miRNA in our SAGE library. These findings suggest that diverse protection strategies appear in the early response of leaves exposed to cold stress. First of all, several genes included in signal transduction through calcium mediated signal sensing, and cascades of several kinases, and transcription factors, were distinguished in the early cold response. Furthermore, genes affecting the synthesis of salicylic acid, nitrate assimilation, ammonia assimilation, the gluconeogenesis pathway, and glucosinolate biosynthesis were newly detected in relationship with cold stress. Finally, our results in the present work provide new insights into the molecular mechanisms involved in transcriptional regulation in response to cold exposure in plants.