© 2007 Heron Publishing—Victoria, Canada
Expressed sequence tags from Cryptomeria japonica sapwood during the drying process
Kazumasa Yoshida (1, 2), Mitsuru Nishiguchi (1), Norihiro Futamura (1) and Tokihiko Nanjo (1)
1. Department of Molecular and Cell Biology, Forestry and Forest Products Research Institute, Tsukuba, Ibaraki 305-8687, Japan / 2. Corresponding author (ykazu@ffpri.affrc.go.jp) / Received October 24, 2005; accepted April 1, 2006; published online October 2, 2006
Summary
Secondary metabolites called norlignans are produced in the xylem of Cryptomeria japonica D. Don. Several norlignans have roles in the defense of sapwood against microbial invasion and in the coloration of heartwood.
The biosynthetic pathway of norlignans is largely unknown. Norlignans have been reported to accumulate in the sapwood during
the drying of C. japonica logs. To search for genes encoding enzymes that catalyze the synthesis of norlignans, we carried out suppression subtractive
hybridization using the fresh sapwood of a felled log and the drying sapwood in which a norlignan, agatharesinol, accumulated.
A total of 1050 expressed sequence tags were obtained from the subtracted cDNA library, and these were assembled into 146
contigs and 361 singletons. Of these 507 unique sequences, 263 were functionally classified into 12 categories. “Metabolism”
was the largest category, with 23% (61) of classified sequences. Twenty-six sequences that encode 16 enzymes were assigned
to “secondary metabolism.” Expression analysis of 15 genes related to “secondary metabolism” revealed that 12 of these genes
had transcripts that were induced during the sapwood drying process. Of the 12 genes, 10 encoded enzymes that use aromatic
compounds as substrates. In addition, 58 sequences representing 22 defense-related proteins were found. Our subtraction library
should be a useful source for isolating genes encoding proteins involved in secondary metabolism including norlignan biosynthesis
and defense in C. japonica xylem.
Keywords:
EST, RT-PCR, suppression subtractive hybridization.
