Cold induced expression of plant defensin and lipid transfer protein transcripts in winter wheat

In winter wheat, low temperature hardening induces a non-specific resistance to snow moulds and other fungi. In a suppressive subtractive hybridization cDNA library between winter wheat unhardened and hardened at 2degreesC, 17% of 186 sequenced cDNA clones were homologous to the small plant defence related proteins, gamma-thionin, gamma-purothionin or non-specific lipid transfer proteins (LTPs), based on their nucleotide sequences or deduced from amino acid sequences. Several partial- and full-length cDNA clones homologous to two defensin proteins (gamma-thionin, subfamily B-2, gamma-purothionin, subfamily I), and non-specific LTPs were isolated. Regulation of defensin transcripts was clearly different from that of the LTPs under controlled environments in the field. The gamma-thionin and gamma-purothionin transcripts were not expressed in unhardened plants grown at 20degreesC, strongly upregulated after 1-3 days hardening at 2degreesC, remained upregulated for 28 days hardening, and disappeared following 1 day of exposure to dehardening conditions at 20degreesC. The LTPs transcripts were constitutively expressed in plants growing at 20degreesC, gradually increased to maximum levels following 14-28 days at hardening, and remained upregulated following 1 and 7 days dehardening. In the field, the gamma-thionin and gamma-purothionin transcripts rapidly increased to maximum levels by mid-November and decreased gradually during the winter until mid-March LTP transcripts were highly expressed in the early autumn, further increased during December-January, then decreased during late winter and early spring. Differences in the pattern and level of expression of these transcripts were evident among cultivars; gamma-thionin expression was associated with freezing resistance among the genotypes tested under both controlled environment and field conditions.