Molecular basis of structural studies, phytochemical characterization and nutritional evaluation of new modified alfalfa in ruminant livestock systems

苜蓿是世界上最重要的牧草之一。苜蓿是一种相对耐寒的哈代和耐旱的豆科植物，具有良好的寿命，具有高营养水平和消化率以及结构与非结构组分的独特比例。苜蓿的一个主要缺点是其过快的瘤胃蛋白质消化的初始速率。这导致严重的消化障碍，如起泡膨胀和低蛋白质效率，从而将高达25%的苜蓿氮从反刍动物释放到环境中。典型的无膨胀豆类饲料含有原花青素（PA）。该特征降低了蛋白质降解的初始速率。PA-蛋白质复合物在瘤胃中形成，减少蛋白质降解，从而增加瘤胃逃逸蛋白并降低泡沫稳定性。由于低pH值，皱胃中的PA-蛋白质键被破坏，这导致小肠中氨基酸消化增加。还发现PA减少甲烷的产生。因此，苜蓿产生适量的饲料PA将是非常有益的反刍家畜生产者。“Lc”是玉米花色素苷调节基因，其形成β-螺旋-环-抑制（bHLH）蛋白。bHLH蛋白通常将MYB蛋白和WD-40蛋白结合在一起以形成刺激花色素和原花色素生物合成基因转录的复合物。今年（2009年），表达C1和Lc基因的新基因修饰的“C1-Lc Alcohol”基因型变得可用。在“C1-Lc苜蓿”牧草中，两个基因的组合应导致比“Lc-苜蓿”（具有单个基因）可能的更高的花青素和原花青素滴度。“ULIMYC-Alcohol”是苜蓿的第二个新基因型，包含来自饲料豆科植物大三叶草的原花青素相关bHLH基因，而不是来自更远的相关谷物玉米。未来五年的研究目标是全面了解影响苜蓿内在结构的单基因和双基因转化（基因组合）的分子基础、氮代谢、微生物氮积累和反刍家畜系统中氮利用效率。

Alfalfa is one of the most important forages in the world. Alfalfa is a relatively winter hardy and drought tolerant legume with good longevity, has high nutrient levels and digestibility and a unique ratio of structural to non-structural components. A major disadvantage of alfalfa is its excessively rapid initial rate of ruminal protein digestion. This results in serious digestive disorders such as frothy bloat and low protein efficiency with consequent release of upto 25% of alfalfa N from the ruminant into the environment. Characteristic bloat-free legume forage has proanthocyanidins (PA). This feature decreases the initial rate of protein degradation. PA-protein complexes are formed in the rumen, reducing protein degradation and consequently increasing ruminal escape protein and reducing foam stability. PA-protein bonds are broken in the abomasum due to low pH, which results in increased amino acid digestion in the small intestine. PA are also found to reduce the production of methane. Therefore, alfalfa that produces moderate amounts of forage PA would be extremely beneficial for ruminant livestock producers. "Lc" is a maize anthocyanin regulatory gene which forms a ß-Helix-Loop-Helix (bHLH) protein. bHLH proteins normally bind together a MYB protein and a WD-40 protein to form a complex that stimulates the transcription of anthocyanidin and proanthocyanidin biosynthetic genes. This year (2009), new gene-modified "C1-Lc Alfalfa" genotypes expressing C1 and Lc genes became available. The combination of the two genes in "C1-Lc alfalfa" forage should result in much higher titres of anthocyanidins and proanthocyanidins than possible with "Lc-Alfalfa" (with single gene). "ULIMYC-Alfalfa" is a 2nd new genotype of alfalfa and contains a proanthocyanidin-related bHLH gene from a forage legume, big trefoil, rather than from more distantly related cereal, maize. The objective of the research in the next five years is to attain a comprehensive understanding of the single and dual gene transformation (gene combination) that influences alfalfa's intrinsic structure on a molecular basis, N metabolism, microbial N accumulation and the efficiency of N utilization in ruminant livestock systems.