Improving Saccharification Efficiency of Alfalfa Stems Through Modification of the Terminal Stages of Monolignol Biosynthesis
Improving Saccharification Efficiency of Alfalfa Stems Through Modification of the Terminal Stages of Monolignol Biosynthesis
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DOI：
10.1007/s12155-008-9020-z
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发表时间：
2008-12-01
影响因子：
3.6
通讯作者：
Dixon, Richard A.
中科院分区：
文献类型：
--
作者：
Jackson, Lisa A.;Shadle, Gail L.;Dixon, Richard A.
建立了一系列的紫花苜蓿转基因株系，其中肉桂酰辅酶A还原酶(CCR)和肉桂醇脱氢酶(CAD)这两种可能的末端酶被反义转基因表达下调。CCR酶活性水平降低到对照水平的10%到65%，CAD活性水平类似地降低到对照水平的5%到40%。在这两个转基因最强下调的品系中，生物量产量降低，但许多品系的木质素水平降低，但生物量和开花时间正常。与对照相比，大多数转基因品系的干物质体外消化率都有所提高。糖化效率是通过直接测量细胞壁糖的释放来确定的，或者通过硫酸预处理和纤维素酶和纤维二糖酶的混合物消化后的糖化效率来确定。与木质素含量相近的CCR品系相比，几个Ccr下调的品系在处理前后的糖化效率显著提高，而CAD下调对糖分释放的影响较小。一个糖化效率提高50%-60%的CCR品系表现出正常的生物量生产，这表明通过对单羟甲基途径进行遗传改造，有可能生产高产的、用于生产生物乙醇的改良原料。
A series of transgenic lines of alfalfa (Medicago sativa) were generated in which either one of the two potentially terminal enzymes of the monolignol pathway, cinnamoyl CoA reductase (CCR) or cinnamyl alcohol dehydrogenase (CAD) was down-regulated by expression of antisense transgenes. Levels of CCR enzymatic activity were reduced to between 10% to 65% of the control level, and levels of CAD activity were similarly reduced to between 5% to 40% of the control. Biomass yields were reduced in the most strongly down-regulated lines for both transgenes, but many of the lines exhibited reduced lignin levels but normal biomass and flowering time. In vitro dry matter digestibility was increased for most transgenic lines compared to controls. Saccharification efficiency was determined by measuring the release of sugars from cell walls directly, or after sulfuric acid pre-treatment and subsequent digestion with a mixture of cellulase and cellobiase. Several CCR down-regulated lines had significantly enhanced saccharification efficiency with both pre-treated and untreated tissues, whereas CAD down-regulation had less impact on sugar release when compared to that from CCR lines with similar lignin contents. One CCR line with a 50-60% improvement in saccharification efficiency exhibited normal biomass production, indicating the potential for producing high yielding, improved feedstocks for bioethanol production through genetic modification of the monolignol pathway.