Analysis of expressed sequence tags from Cryptomeria japonica pollen reveals novel pollen-specific transcripts

Cryptomeriajaponica D. Don is one of the most important forest trees in Japan, but more than 10% of the Japanese population is allergic to its pollen. We constructed a cDNA library derived from pollen grains of C japonica and performed an analysis of expressed sequence tags (ESTs). We obtained partial sequences from 1929 clones, which represented 1365 unique transcripts. Among the unique transcripts, 984 (72%) encoded proteins that were similar to Arabidopsis proteins with E-values of < 10(-5). Analysis of funtional composition of the pollen ESTs revealed the overrepresentation of mRNAs for proteins involved in protein synthesis and post-translational modification. The most abundant transcripts were derived from novel genes (CjMP1-related genes) and encoded proteins that were not homologous to any proteins in current databases. The CjMP1-related genes formed a multi-gene family and were expressed specifically in the pollen grains of C.japonica. An analysis of homologies between ESTs from C. japonica pollen and proteins in the Structural Database of Allergenic Proteins revealed that products of 48 of the clones (2.5%) exhibited significant homology to known plant allergens. Our results provide new information about pollen-specific genes and potential allergens in C. japonica pollen.