Ectopic expression of ABI3 gene enhances freezing tolerance in response toabscisic acid and low temperature in Arabidopsis thaliana

The plant hormone abscisic acid (ABA) regulates several physiological and d evelopmental processes in plants, including stress adaptation and seed matu ration. ABA-mediated processes appear to be central in plant cold acclimati on and expression of cold acclimation-related genes. Ectopic expression of ABI3 encoding a seed-specific transcriptional activator confers on Arabidop sis vegetative tissues the ability to accumulate seed-specific transcripts in response to ABA, and also influences some ABA-mediated vegetative respon ses. In the present study we characterized the effect of ectopic expression of ABI3 on cold acclimation and development of freezing tolerance in Arabi dopsis. We first determined the effect of ABI3 on ABA-induced expression of cold acclimation-related genes. Expression of ABI3 increased the ABA-induc ed accumulation of transcripts for several ABA/cold/drought-responsive gene s such as RAB18 and LTI78. Enhanced expression of these genes was evident e ven after transient application of ABA, and the enhanced expression was cor related with increased freezing tolerance in ABI3 transgenic plants. Ectopi c expression of ABI3 also appeared to modulate low temperature-induced free zing tolerance. The ABI3 transgenic plants acclimated faster than the wild- type plants, and the maximum tolerance obtained was significantly higher. T hese data showed that lower levels of ABA were needed to trigger the expres sion of the genes and to maintain the freezing-tolerant state in the ABI3 t ransgenic plants, and indicate that ectopic expression of ABI3 leads to enh anced responsiveness to ABA. The ectopic expression of ABI3 could provide a new strategy for engineering plant stress tolerance.