2010 Volume 60 Issue 4 Pages 314-323
Lignin, one of the major components of plant cell walls, has negative impacts on forage digestibility and bioethanol production through fermentation. Understanding the regulatory mechanism of lignin biosynthesis is essential to developing plants with altered lignin contents. The sorghum (Sorghum bicolor [L.] Moench) brown-midrib-6 mutant (bmr-6) has reduced levels of several key enzymes in the lignin biosynthesis pathway. Among the genes encoding these enzymes, the gene for cinnamyl alcohol dehydrogenase (CAD; EC 1.1.1.195) contains a nonsense mutation (responsible for bmr-6) that results in reduced CAD gene transcript levels. We found that the CAD coding region was 4225 bp and consisted of four exons separated by three introns. Bioinformatic analysis of the 5′-flanking region identified several putative binding sites for transcription factors. Moreover, a cross-species comparison of CAD genomic DNA sequences revealed evolutionary and structural variation among plant taxa. The expression level of the CAD gene was much lower in bmr-6 than in normal isoline (N-6) in root, stem, leaf, and midrib. Expression levels of other lignin biosynthesis genes were comparable in bmr-6 and N-6. These results suggest that the depression of CAD enzymatic activity in bmr-6 could affect enzymatic activity and post-translational regulation of other enzymes related to lignin biosynthesis.
