Transgenic tobacco plants expressing PicW gene from Picea wilsonii exhibit enhanced freezing tolerance

A cold-induced gene of 669 bp in length without introns, PicW, was cloned from Picea. wilsonii, a cold tolerant conifer species. Sequence analysis showed that it was a member of the dehydrin family because of its conserved amino acid constitution and protein secondary structure. The protein was rich in hydrophilic amino acids such as alanine, lysine, glutamic acid, glutamine and threonine, but devoid of two hydrophobic amino acids, cysteine and tryptophan. The PicW gene contained five repeated motifs homologous to the core K-segment in dehydrins. Protein secondary structure prediction showed that PicW comprised 29 % alpha-helix, mostly in the K-homologous segment, and random coils. The PicW gene was cloned into the expression vector PEZR(K)-LC under the 35S promoter and transformed into tobacco plants. After treatment at -5 A degrees C for 3 h, all of the tobacco plants were wilting. However, the transgenic plants showed better growth performance than wild-type plants. Further tests of physiological indexes including relative electrolyte leakage and malondialdehyde content, proline and soluble sugar content also revealed significant differences between the wild-type and transgenic tobacco plants. It was concluded that the PicW gene could be an important gene resource for freezing-tolerant plant breeding.