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Abstract Detail


Secondary Metabolism

Jackson, Lisa A. [1], Chen, Fang [2], Nakashima, Jin [2], Shadle, Gail L. [2], Dixon, Richard [2].

Cinnamoyl CoA reductase down-regulation and its impact on forage quality in alfalfa (Medicago sativa).

Lignin gives mechanical strength to the cell wall and plays a key role in allowing efficient conductance of water through the vascular tissue in plant stems. Lignin is composed of building blocks called monolignols. The primary units of lignin are guaiacyl (G), syringyl (S) and p-hydroxyphenyl (H). Lignin is recalcitrant to digestion by most cell wall degrading enzymes, and physically prevents digestion of plant cell wall polysaccharides, thereby reducing forage quality. For this reason, there is great interest in modifying lignin content/composition in forage legumes such as alfalfa. We are studying the effects of down-regulating the individual genes in the monolignol biosynthesis pathway in transgenic alfalfa. The cinnamoyl CoA reductase (CCR) gene (TC106830) from M. truncatula was used to down-regulate the corresponding CCR gene in alfalfa through expression of an antisense construct. An increased S/G ratio has been observed in other plant species that are down-regulated in CCR. It has been proposed that this is due to a decrease in extractable G units. However, a reduction in S units has also been reported, consistent with the targeted CCR gene being involved in the synthesis of both G and S lignin. We have obtained 60 independent transgenic alfalfa lines harboring a CCR antisense transgene. As shown by RT-PCR and Northern analysis, fifteen of these lines are down-regulated in CCR expression, but to varying degrees. Enzyme assays show a decrease in percent relative activity for all down-regulated lines. Many of the CCR down-regulated plant lines show an increase in percent digestibility. Lignin content for the most of the transgenic alfalfa lines is very similar to the controls. Lignin composition results will also be presented in the poster.


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1 - Samuel Roberts Noble Foundation, Plant Biology Division, 2510 Sam Noble Pkwy, Ardmore, Ok, 73401, USA
2 - Samuel Roberts Noble Foundation, Plant Biology Division

Keywords:
lignin
digestibility
alfalfa
CCR.

Presentation Type: Plant Biology Abstract
Session: P
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM
Number: P20031
Abstract ID:989


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