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。紫花苜蓿是一种耐寒耐旱的豆科植物，具有较高的营养水平和消化率，具有独特的结构成分与非结构成分的比例。苜蓿的一个主要缺点是其瘤胃蛋白质消化的初始速度过快。这会导致严重的消化系统紊乱，如泡沫性腹胀和蛋白质效率低，从而使反刍动物将高达25%的苜蓿氮释放到环境中。豆科饲料中含有原花青素（PA）。这一特性降低了蛋白质降解的初始速率。pa -蛋白复合物在瘤胃内形成，减少蛋白质降解，从而增加瘤胃逃逸蛋白，降低泡沫稳定性。由于pH值低，皱胃中的pa蛋白键断裂，导致小肠中氨基酸消化增加。PA还被发现可以减少甲烷的产生。因此，生产适量牧草PA的苜蓿对反刍家畜养殖者极为有益。“Lc”是玉米花青素调控基因，形成ß-Helix-Loop-Helix （bHLH）蛋白。bHLH蛋白通常与MYB蛋白和WD-40蛋白结合形成一个复合物，刺激花青素和原花青素生物合成基因的转录。今年（2009年），新的基因修饰的“C1-Lc苜蓿”基因型表达C1和Lc基因成为可能。这两个基因在“C1-Lc紫花苜蓿”草料中的组合，其花青素和原花青素的含量要比“lc -苜蓿”（单基因）高得多。“ULIMYC-Alfalfa”是紫花苜蓿的第二个新基因型，它含有一个与原花青素相关的bHLH基因，该基因来自一种牧草豆科植物，大三叶草，而不是来自更近的谷物，玉米。未来5年的研究目标是全面了解反刍家畜系统中影响紫花苜蓿内在分子结构、氮代谢、微生物氮积累和氮利用效率的单基因和双基因转化（基因组合）。

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.