Overexpression of a ItICE1 gene from Isatis tinctoria enhances cold tolerance in rice

ItICE1, a ICE1-like gene, was isolated from a cDNA library from cold-treated woad (Isatis tinctoria L.) tissues. Expression analysis revealed that the ItICE1 gene was expressed constitutively and was predominant in the leaves of woad seedlings and that its mRNA accumulation was altered by salt stress and abscisic acid application, but not by dehydration and cold stresses. The transgenic rice lines overexpressing ItICE1 showed no growth retardation under normal growth conditions as well as enhanced tolerance to cold stress. Physiological assays showed that ItICE1 not only increased the accumulation of free proline and chlorophyll in transgenic rice lines under cold stress, but also reduced malondialdehyde content and electrolyte leakage. The analysis of gene expression in transgenic rice lines indicated that the maize ubiquitin promoter could respond to cold stress and upregulate ItICE1 gene expression level under its control. Under cold stress conditions, transgenic lines had a remarkably increased expression of OsDREB1A, J013078A14, 001-125-G03, 001-023-B08 and J023042N13 compared to wild-type plants (P < 0.05), implying that ItICE1 functions in the CBF/DREB1 cold-response pathway. These results demonstrate that ItICE1 plays an important regulatory role in the improvement of tolerance to cold stress in rice and is potentially useful for improving the cold tolerance of other plants.