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

紫花苜蓿是世界上最重要的牧草之一。紫花苜蓿是一种耐寒性和耐旱性较强的豆科牧草，寿命长，营养水平高，消化率高，结构成分与非结构成分的比例独特。紫花苜蓿的一个主要缺点是其瘤胃蛋白质的初始消化速度过快。这会导致严重的消化障碍，如泡沫肿胀和蛋白质效率低下，从而导致高达25%的紫花苜蓿氮从反刍动物释放到环境中。典型的无胀豆科牧草含有原花青素(PA)。这一特性降低了蛋白质的初始降解速度。PA-蛋白质复合体在瘤胃中形成，减少蛋白质的降解，从而增加瘤胃逃逸蛋白，降低泡沫稳定性。由于低pH值，皱胃中的PA蛋白键断裂，导致小肠中氨基酸的消化增加。PA还被发现可以减少甲烷的产生。因此，生产适量饲料PA的紫花苜蓿对反刍动物畜牧业生产者非常有利。“LC”是一个玉米花青素调节基因，它形成了一种？螺旋-环-螺旋(BHLH)蛋白。BHLH蛋白通常将MYB蛋白和WD-40蛋白结合在一起，形成一个复合体，刺激花青素和原花青素生物合成基因的转录。今年(2009)，新的表达C1和LC基因的转基因“C1-LC紫花苜蓿”基因型问世。将这两个基因结合在一起，可使花青素和原花青素的含量大大高于单一基因的花青素和原花青素。“ULIMYC-紫花苜蓿”是紫花苜蓿的第二个新基因型，它包含一个与原花青素相关的bHLH基因，该基因来自饲用豆科植物大三叶草，而不是来自更远缘关系的谷物玉米。未来五年的研究目标是全面了解单基因和双基因转化(基因组合)对紫花苜蓿内在结构、氮素代谢、微生物氮素积累和反刍动物系统氮素利用效率的影响。

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.