Grün Sebastian, Frey Monika, Gierl Alfons
Institute for Biochemical Plant Pathology, GSF-National Research Center for Environment and Health, Ingolstädter Landstrasse 1, D-85746 Neuherberg, Germany.
Phytochemistry. 2005 Jun;66(11):1264-72. doi: 10.1016/j.phytochem.2005.01.024.
Two indole alkaloids with defense related functions are synthesized in the genus Hordeum of the Triticeae. Gramine (3(dimethyl-amino-methyl)-indole) is found in H. spontaneum and in some varieties of H. vulgare, the benzoxazinoid 2,4-dihydroxy-2H-1,4-benzoxazin-3(4H)-one (DIBOA) is detected in H. roshevitzii, H. brachyantherum, H. flexuosum, H. lechleri. Biosynthesis of DIBOA and of gramine was found to be mutually exclusive in wild Hordeum species, indicating that there was selection against simultaneous expression of both pathways during evolution. The full set of genes required for DIBOA biosynthesis in H.lechleri was isolated and the respective enzyme functions were analyzed by heterologous expression. The cytochrome P450 genes Bx2-Bx5 demonstrate a monophyletic origin for H. lechleri, Triticum aestivum and Zea mays. HlBx2-HlBx5 share highest homology to the orthologous genes of T. aestivum. In contrast, the branch point enzyme of the DIBOA pathway, the indole-3-glycerol phosphate lyase BX1, might have evolved independently in H. lechleri. In all Hordeum species that synthesize DIBOA, DNA sequences homologous to Bx genes are found. In contrast, these sequences are not detectable in the genomes of H. vulgare and H. spontaneum that do not synthesize benzoxazinoids.
小麦族大麦属中合成了两种具有防御相关功能的吲哚生物碱。在野生大麦和一些栽培大麦品种中发现了禾草碱（3 - （二甲基 - 氨基甲基） - 吲哚），在罗氏大麦、短花药大麦、弯曲大麦、糙稃大麦中检测到苯并恶嗪类化合物2,4 - 二羟基 - 2H - 1,4 - 苯并恶嗪 - 3(4H) - 酮（DIBOA）。在野生大麦物种中，发现DIBOA和禾草碱的生物合成相互排斥，这表明在进化过程中存在对两条途径同时表达的选择抑制。分离出了糙稃大麦中DIBOA生物合成所需的全套基因，并通过异源表达分析了各自的酶功能。细胞色素P450基因Bx2 - Bx5显示出糙稃大麦、普通小麦和玉米具有单系起源。HlBx2 - HlBx5与普通小麦的直系同源基因具有最高的同源性。相比之下，DIBOA途径的分支点酶吲哚 - 3 - 甘油磷酸裂解酶BX1可能在糙稃大麦中独立进化。在所有合成DIBOA的大麦物种中，都发现了与Bx基因同源的DNA序列。相反，在不合成苯并恶嗪类化合物的栽培大麦和野生大麦基因组中未检测到这些序列。
