Abstract: Basal angiosperms contain a wide diversity of floral and growth forms and gave rise to the largest recent angiosperm lineages. As none of the basal angiosperm genomes has been sequenced, examining large bacterial artificial chromosome (BAC) inserts remains the main approach to providing a first glimpse of the structure and organization of their genomes. In this study, we sequenced a 126.9-kbp BAC contig harboring a cinnamyl alcohol dehydrogenase gene (LtuCAD1) in a basal angiosperm species, Liriodendron tulipifera L., an important timber tree species with significant ecological and economic values. A key enzyme in lignin biosynthesis, CAD catalyzes the final step in the synthesis of monolignols. We carried out phylogenetic analyses of seven full-length CAD family genes (LtuCAD1–7) obtained from a comprehensive Liriodendron expressed sequence tag dataset. The phylogenetic tree suggests that LtuCAD1 is the primary CAD gene involved in lignifications as it is the only Liriodendron CAD grouped with the bona fide CADs class. As well as the LtuCAD1, the BAC contig contained fragmented sequences for one integrase, eight hypothetical proteins, two gag-pol polyproteins, one RNase H family protein, and one chromatin binding protein. Comparative analysis with other angiosperm species suggests that the genomic segment in this BAC has undergone frequent arrangement. This study is our initial step in identifying and understanding lignin biosynthesis genes from basal angiosperm species. Such knowledge can help bridge the information gap between hardwood (angiosperm) and softwood (gymnosperm) species and benefit potential breeding and biotechnology application for enhanced production of biomass and digestibility in L. tulipifera.

Key words: BAC contig, cinnamyl alcohol dehydrogenase (CAD), gene order, lignin biosynthesis, synteny.