The molecular biology of plant acclimation to low temperature

In many temperate plant species, a period of exposure to a low positive temperature will acclimate the plants to withstand a subsequent freezing stress. A number of plant genes, which are up-regulated at steady-state mRNA levels by an acclimation treatment, have been isolated from both monocotyledon and dicotyledon species. Most of these genes are also responsive to a drought treatment and/or abscisic acid. The acclimation of plants to freezing stress is a complex process and although genetic studies in some species have identified genes with a major effect, in general, the inheritance of frost tolerance is multigenic. In view of this, it is not surprising that a range of different genes have been cloned. The precise function of the proteins encoded by these genes is unknown. However, analysis of predicted protein products and studies of recombinant proteins, together with detailed expression studies, are beginning to provide information about some of the genes. Both transcriptional and post-transcriptional controls have been shown to be involved in the expression of these genes. Although studies of RNA stabilizing systems are still in their early stages, a number of low temperature responsive promoters have been studied using reporter gene constructs. Other approaches to the molecular analysis of cold acclimation include the isolation of non-acclimating mutants and the production of transgenic plants.