Involvement of cinnamyl-alcohol dehydrogenase in the control of lignin formation in Sorghum bicolor L. Moench

Abstract

The lignin structure and enzyme activities of normal and brown-midrib (BMR-6) mutant lines of Sorghum bicolor have been compared to identify the enzyme(s) involved in the reduction of the lignin content of the mutant. The results indicate that cinnamyl-alcohol dehydrogenase (CAD) and caffeic acid O-methyltransferase are depressed in the BMR-6 line, whereas the structural modifications correspond only to a reduction of CAD activity. Apparently, the change in the Sorghum lignin content, caused by depression of CAD activity, is accompanied by the incorporation of cinnamaldehydes into the core lignin.

Genetic background impacts soluble and cell wall-bound aromatics in brown midrib mutants of sorghum

“…Lowered CAD activity in bmr-6 plants as compared to WT has been reported earlier (Pillonel et al 1991). In contrast, our data suggest that stem extracts from both the near-isogenic CAD-deWcient bmr-6 and DM plants in the two diVerent sorghum backgrounds tested had no measureable activity against coniferyl alcohol under the assay conditions employed.…”

“…Researchers have previously examined lignin and phenolic signatures in bmr-sorghum plants (Pillonel et al 1991;Lam et al 1996;Suzuki et al 1997;HatWeld et al 1999;Bout and Vermerris 2003). These studies focused on evaluating components of a single bmr mutant in one genetic background or attempted to compare bmr mutants in diVerent genetic backgrounds.…”

“…Finally, changes in lignin content and composition can be expected in tissues that are ligniWed at maturity, such as the xylem, vascular bundle Wber sheaths, and cortical schlerenchyma. Earlier studies using leaf tissues have conWrmed some of these predictions showing that bmr-6 and bmr-12 plants have less lignin, have reduced amounts of cell wall-bound pCA esters, and have altered S-to G-lignin ratios as compared to wild-type plants (Akin et al 1986;Pillonel et al 1991;Bout and Vermerris 2003).…”

“…Pillonel et al (1991) characterized sorghum bmr-6 as a mutation principally aVecting cinnamyl alcohol dehydrogenase (CAD) activity, although a mutation in the CAD gene has not yet been identiWed. Plants carrying this mutation displayed reduced levels of lignin and incorporation of cinnamylaldehydes into the lignin polymer.…”

“…Plants carrying this mutation displayed reduced levels of lignin and incorporation of cinnamylaldehydes into the lignin polymer. Interestingly, these bmr-6 plants also displayed decreased levels of caVeic acid O-methyl transferase (COMT) (Pillonel et al 1991). Bout and Vermerris (2003) identiWed a nonsense mutation in a COMT gene responsible for the bmr-12 phenotype in sorghum plants.…”