[Show abstract][Hide abstract] ABSTRACT: Cinnamyl alcohol dehydrogenase (CAD: EC 220.127.116.11) catalyzes the conversion of p-hydroxycinnamaldehydes to the corresponding alcohols and is considered the last step in the synthesis of the monomeric precursors of lignin (a phenolic polymer found in vascular plant cell walls). However, lignin synthesis is still poorly understood, and the comparison between the different CADs is difficult because more than 100 protein sequences have been assigned as CADs, in spite of a low degree of identity between them and a lack of demonstration of biochemical function for most of them. The objective of this work was to analyze the evolution and diversity of this group of proteins, since analyses on the evolution of this group of enzymes are lacking, and such analysis might help to define either the different subfamilies that constitute the CAD family, as the individual proteins belonging to each subfamily.
The obtained results showed that the CAD family comprises three different protein subfamilies with at least 36% of identity: (1) CAD subfamily, contains the enzymes most efficient to reduce cinnamaldehydes and correspond to the bona fide CADs; they are present in both angiosperms and gymnosperms. (2) ELI3 subfamily, corresponds to enzymes found only in angiosperms; they are described as elicitor-inducible defense-related plant proteins, with cinnamyl alcohol dehydrogenase, benzyl alcohol dehydrogenase or mannitol dehydrogenase activity. (3) CAD-related subfamily, which contains enzymes not involved in lignin biosynthesis, and probably constitutes a group comprised by several paralogous related proteins with high identity among them; they exist in bacteria and fungi.
Enzymology and Molecular Biology of Carbonyl Metabolism—12, Edited by Henry Weiner, Bryce Plapp, Ronald Lindahl, Edmund Maser, 01/2006: chapter Evolution of Cinnamyl Alcohol Dehydrogenase Family: pages 142-153; Purdue University Press. West Lafayette, Indiana., ISBN: 978-1-55753-384-5
[Show abstract][Hide abstract] ABSTRACT: Cells associated with veins of petioles of C3 tobacco possess high activities of the decarboxylase enzymes required in C4 photosynthesis. It is not clear whether this is the case in other C3 species, nor whether these enzymes provide precursors for specific biosynthetic pathways. Here, we investigate the activity of C4 acid decarboxylases in the mid-vein of Arabidopsis, identify regulatory regions sufficient for this activity, and determine the impact of removing individual isoforms of each protein on mid-vein metabolite profiles. This showed that radiolabelled malate and bicarbonate fed to the xylem stream were incorporated into soluble and insoluble material in the mid-vein of Arabidopsis leaves. Compared with the leaf lamina, mid-veins possessed high activities of NADP-dependent malic enzyme (NADP-ME), NAD-dependent malic enzyme (NAD-ME) and phosphoenolpyruvate carboxykinase (PEPCK). Transcripts derived from both NAD-ME, one PCK and two of the four NADP-ME genes were detectable in these veinal cells. The promoters of each decarboxylase gene were sufficient for expression in mid-veins. Analysis of insertional mutants revealed that cytosolic NADP-ME2 is responsible for 80% of NADP-ME activity in mid-veins. Removing individual decarboxylases affected the abundance of amino acids derived from pyruvate and phosphoenolpyruvate. Reducing cytosolic NADP-ME activity preferentially affected the sugar content, whereas abolishing NAD-ME affected both the amino acid and the glucosamine content of mid-veins.
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