Transcription factors involved in cold response in plants.

Abstract

Studies in Arabidopsis have shown cold stress tolerance can be enhanced by manipulation of the CBF/DREB and ICE transcription factor genes. To date, few studies have investigated CBF and ICE genes in crops species such as barley. Using a C-repeat element as bait, two CBF genes were isolated from a cold-stressed barley cDNA library, HvCBF16 and HvCBF23. HvCBF16 was induced by cold treatment but not by other abiotic stresses. HvCBF23 was constitutively expressed and was not induced by cold treatment. The analysis of transgenic plants expressing these genes will determine their importance in cold tolerance. Transgenic barley plants expressing the barley gene HvCBF2A were found to be more cold tolerant in controlled temperature trials, and hence were assayed to determine the basis of their acquired phenotype. Northern and qRT-PCR analysis showed that four genes known to be involved in cold tolerance were significantly upregulated. Importantly the increased expression was proportional to the level of transgene expression and levels were higher following cold treatment. A homolog of the Arabidopsis ICE transcription factor was isolated from a freezing-tolerant barley variety (Hordeum vulgare L. cv. Haruna Nijo) and transcript analysis of HvICE2 under various abiotic stresses showed that expression of HvICE2 was induced at low temperatures, particularly in floral tissues. HvICE2 was over-expressed using the maize ubiquitin constitutive promoter in transgenic barley. Expression analysis of putative downstream genes, including various COR genes, in the transgenic plants before and during cold treatment did not reveal any alteration in expression. This suggests HvICE2 that the COR genes studied are not targets of HvICE2 or that additional factors or conditions are required for effective function of HvICE2. Transgenic Arabidopsis plants were produced with over- or reduced-expression of the uncharacterised ICE gene, AtICE2. The cold tolerance of the AtICE2 transgenic lines was not significantly different from wild type plants.