Improved forage digestibility of tall fescue (Festuca arundinacea) by transgenic down‐regulation of cinnamyl alcohol dehydrogenase

Abstract

SummaryLignification of cell walls during plant development has been identified as the major factor limiting forage digestibility and concomitantly animal productivity. cDNA sequences encoding a key lignin biosynthetic enzyme, cinnamyl alcohol dehydrogenase (CAD), were cloned from the widely grown monocotyledonous forage species tall fescue ( Festuca arundinacea Schreb.). Recombinant tall fescue CAD expressed in E. coli exhibited the highest V max / K m values when coniferaldehyde and sinapaldehyde were used as substrates.Transgenic tall fescue plants carrying either sense or antisense CAD gene constructs were obtained by microprojectile bombardment of single genotype-derived embryogenic suspension cells. Severely reduced levels of mRNA transcripts and significantly reduced CAD enzymatic activities were found in two transgenic plants carrying sense and antisense CAD transgenes, respectively. These CAD down-regulated transgenic lines had significantly decreased lignin content and altered ratios of syringyl (S) to guaiacyl (G), G to p -hydroxyphenyl (H) and S to H units. No significant changes in cellulose, hemicellulose, neutral sugar composition, p -coumaric acid and ferulic acid levels were observed in the transgenic plants. Increases of in vitro dry matter digestibility of 7.2 -9.5% were achieved in the CAD down-regulated lines, thus providing a novel germplasm to be used for the development of grass cultivars with improved forage quality.

Targeted down-regulation of cytochrome P450 enzymes for forage quality improvement in alfalfa ( Medicago sativa L.)

“…Improvements in alfalfa forage digestibility by downregulation of the ''late'' pathway enzymes COMT and CAD (28)(29)(30) are considerably less than achieved here with C3H or C4H down-regulation. For development of agronomically viable lines, it may be necessary to further fine-tune the level of C3H or C4H expression to eliminate the possibility of reduced growth.…”

“…1 have been identified, and many of the enzymatic steps have been down-regulated in transgenic plants. The results of these studies (24)(25)(26)(27)(28)(29)(30) have generally confirmed the pathway in Fig. 1 and supported increasing S͞G ratio as a means of improving paper pulping in trees.…”

Monolignol Biosynthesis and its Genetic Manipulation: The Good, the Bad, and the Ugly

“…but not H units, and decreased S/G ratio (Chen et al, 2003). The in vitro dry matter digestibility is increased by 7.2-9.5% compared to controls (Chen et al, 2003).…”

“…Coniferaldehyde and sinapaldehyde are preferred substrates for CAD in tall fescue (Chen et al, 2003).…”

“…The in vitro dry matter digestibility is increased by 7.2-9.5% compared to controls (Chen et al, 2003). Similarly, CAD down-regulation in switchgrass results in a 27 14-22% reduction in lignin content and decreased S/G ratio, no changes in wall-bound phenolics, an increase in soluble chlorogenic acid content, and up to 20% increased digestibility and 15-35% increased saccharification efficiency (Fu et al, 2011).…”