Submitted to: Planta
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/17/2004
Publication Date: 9/25/2004
Citation: Tobias, C.M., Chow, E.K. 2004. Structure of the Cinnamyl-Alcohol Dehydrogenase Gene Family in Rice and Promoter Activity of a Member Associated with Lignification. Planta. 220:678-688. Interpretive Summary: At the present, genes involved in the pathway toward synthesis of monolignols in grasses have been characterized individually with respect to their biochemical activity, expression pattern, and mutant phenotypes. With the advent of the complete genome sequence of rice, a fuller understanding of this metabolic pathway must include a comparative analysis of all gene family members present that may participate in controlling lignin deposition. For this reason we have undertaken analysis of the CAD gene family in rice. Here we describe twelve rice CAD family members that may play significant roles in lignin biosynthesis. One of the gene family members was found to be an apparent orthologue of the CAD gene at the bm1 locus of maize. Its expression pattern was determined through reporter gene analysis.
Technical Abstract: Analysis of lignification in rice has been facilitated by the availability of the recently completed rice genome sequence and rice will serve as an important model for understanding the relationship of grass lignin composition to cell wall digestibility. Cinnamyl alcohol dehydrogenase is an enzyme important in lignin biosynthesis. The genome of rice contains 12 distinct genes with significant similarity to cinnamyl alcohol dehydrogenases (CAD) that are present at nine different loci in the rice genome. The rice gene family is diverse with respect to other angiosperm and gymnosperm CAD genes isolated to date and contains one member (OsCAD6) that is substantially diverged relative to other family members that contains a peroxisomal targeting signal. Four closely related family members (OsCAD8A-D) are present at the same locus and represent the product of a localized gene duplication and inversion. Promoter-reporter gene fusions to OsCAD2, an orthologue of the bm1 (brown midr!ib 1) locus of maize, reveals that in rice expression of this gene is associated with vascular tissue in aerial parts of the plant and is correlated with the onset of lignification. In root tissue expression is primarily in the cortical parenchyma adjacent to the exodermis and in vascular tissue of the root.