The molecular characterization of a set of cDNAs differentially expressed during Douglas‐fir germination and early seedling development

We constructed a cDNA library with mRNA pooled from 4‐ to 6‐day‐old Douglas‐fir (Pseudotsuga menziesii [Mirb.] Franco) seedlings. To identify genes with increased expression during germination and early seedling development, the library was screened differentially with cDNA probes synthesized using mRNA isolated from mature seeds and 6‐day‐old seedlings. Partial DNA sequence analysis and predicted amino acid sequences revealed cDNA clones with homology to several plant proteins including: a chaperonin 60β (cpn60β), a low molecular weight heat shock protein (LMW HSP), a luminal binding protein (BiP), a type II chlorophyll a/b‐binding protein (CAB) and a cysteine protease. In mature seeds, transcripts corresponding to each cDNA clone were detected and their levels increased after 2 days of exposure to the germination conditions. The clone that shares identity with the cysteine protease (DF3‐3) and DF6‐7 had peak transcript levels during the germination phase, whereas the cpn60β (DF3), a LMW HSP (DF4‐5), BiP (DF5‐1) and CAB (DF6‐3) showed peaks during the post‐germination phase. All the transcripts were present at lower levels in 10‐week‐old needles except for CAB. As a comparison, an additional clone which was present at similar levels in both mature seeds and in 6‐day‐old seedlings was isolated and found to be homologous to a NADPH‐cytochrome P450 reductase (CPR) (EC 1.6.2.4). The expression of CPR changed little during germination and early seedling development with lower transcript levels in 10‐week‐old needles. The significance of the individual genes, their expression, and possible roles during germination is discussed.