Nomura Taiji, Ishizuka Akihiro, Kishida Kazunori, Islam A K M Rafiqul, Endo Takashi R, Iwamura Hajime, Ishihara Atsushi
Division of Applied Biosciences, Graduate School of Agriculture, Kyoto University, Japan.
Genes Genet Syst. 2007 Dec;82(6):455-64. doi: 10.1266/ggs.82.455.
Hordatines A and B, the strong antifungal compounds in barley (Hordeum vulgare), are biosynthesized from p-coumaroyl- and feruloyl-CoA and agmatine by two successive reactions catalyzed by agmatine coumaroyltransferase (ACT) and peroxidase. ACT catalyzes the formation of agmatine conjugates (p-coumaroylagmatine and feruloylagmatine) from precursor CoAs and agmatine, and peroxidase catalyzes the oxidative coupling of agmatine conjugates to form hordatines. Our previous study demonstrated that the short arm of barley chromosome 2H (2HS) is responsible for the biosynthesis of hordatines. In the present study, however, barley genes encoding the ACT (HvACT) and a peroxidase (HvPrx7) were found to be located on the long arm of 2H (2HL). The amounts of hordatines and precursor agmatine conjugates were analyzed in wheat (Triticum aestivum) and wheat lines carrying a whole 2H chromosome, 2HS or 2HL. The addition of 2H and 2HL elevated the levels of agmatine conjugates in wheat. This could be attributed to the HvACT on 2HL. However, the content of agmatine conjugates increased also in the 2HS addition line, suggesting the presence of another unidentified ACT gene on 2HS. Hordatines were detected in wheat, but their content was by far lower than those in barley. The 2H and 2HS addition lines accumulated substantial amounts of hordatines, while the 2HL addition line accumulated them as little as wheat did in spite of the substantial transcription of the HvPrx7 gene on 2HL and of the increased accumulation of the precursor agmatine conjugates. These facts suggest that the HvPrx7 gene on 2HL is not involved in the hordatine biosynthesis and that unidentified peroxidase gene responsible for the hordatine biosynthesis is located on 2HS in barley.
大麦（Hordeum vulgare）中的强抗真菌化合物大麦碱A和B，是由对香豆酰辅酶A、阿魏酰辅酶A和胍丁胺通过胍丁胺香豆酰转移酶（ACT）和过氧化物酶催化的两个连续反应生物合成的。ACT催化前体辅酶A和胍丁胺形成胍丁胺共轭物（对香豆酰胍丁胺和阿魏酰胍丁胺），过氧化物酶催化胍丁胺共轭物的氧化偶联形成大麦碱。我们之前的研究表明，大麦2H染色体的短臂（2HS）负责大麦碱的生物合成。然而，在本研究中，发现编码ACT（HvACT）和一种过氧化物酶（HvPrx7）的大麦基因位于2H的长臂（2HL）上。分析了携带完整2H染色体、2HS或2HL的小麦（Triticum aestivum）和小麦品系中大麦碱和前体胍丁胺共轭物的含量。添加2H和2HL提高了小麦中胍丁胺共轭物的水平。这可能归因于2HL上的HvACT。然而，在添加2HS的品系中，胍丁胺共轭物的含量也增加了，这表明2HS上存在另一个未鉴定的ACT基因。在小麦中检测到了大麦碱，但其含量远低于大麦中的含量。添加2H和2HS的品系积累了大量的大麦碱，而添加2HL的品系尽管2HL上的HvPrx7基因大量转录且前体胍丁胺共轭物积累增加，但积累的大麦碱与小麦一样少。这些事实表明，2HL上的HvPrx7基因不参与大麦碱的生物合成，而负责大麦碱生物合成的未鉴定过氧化物酶基因位于大麦的2HS上。
