High expression level of a gene coding for a chloroplastic amino acid selective channel protein is correlated to cold acclimation in cereals

A cold-regulated gene (cor tmc-ap3) coding for a putative chloroplastic ami no acid selective channel protein was isolated from cold-treated barley lea ves combining the differential display and the 5'-RACE techniques. Cor tmc- ap3 is expressed at low level under normal growing temperature, and its exp ression is strongly enhanced after cold treatment. A positive correlation b etween the expression of cor tmc-ap3 and frost tolerance was found both amo ng barley cultivars and among cereal species. The COR TMC-AP3 protein was e xpressed in vitro, purified and used to raise a polyclonal antibody. Wester n analysis showed that the cor tmc-ap3 gene product is localized to the chl oroplastic outer envelope fraction, supporting its putative function. The f rost-resistant winter cultivar Onice accumulated COR TMC-AP3 more rapidly a nd at a higher level than the frost-susceptible spring cultivar Gitane. Aft er 28 days of cold acclimation the winter cultivar had about 2-fold more pr otein than the spring genotype. All these results suggest that an increased amount of a chloroplastic amino acid selective channel protein could be re quired for cold acclimation in cereals. Hypotheses about the role of COR TM C-AP3 during the hardening process are discussed.