Three genomes differentially contribute to the biosynthesis of benzoxazinones in hexaploid wheat
Three genomes differentially contribute to the biosynthesis of benzoxazinones in hexaploid wheat
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DOI：
10.1073/pnas.0505156102
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发表时间：
2005-11-08
影响因子：
11.1
通讯作者：
Iwamura, H
中科院分区：
文献类型：
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作者：
Nomura, T;Ishihara, A;Iwamura, H
六倍体小麦（Triticum aestivum）积累苯并恶嗪酮（Bxs）作为防御化合物。在此之前，我们发现五个Bx生物合成基因TaBx 1-TaBx 5分别位于六倍体小麦的三个基因组（A、B和D）上。在这项研究中，我们分离了每个TaBx基因的三个同源同源cDNA，以估计单个同源TaBx基因对六倍体小麦Bxs生物合成的贡献。我们分析了他们的转录水平同源或基因组特异性定量RTPCR和动力学分析，使用重组TaBX酶的翻译产物的催化性能。这三种同源同源物的转录有差异，并且个体同源物转录物与总同源物转录物的比率也随组织而变化，即，芽或根，以及发育阶段。此外，三个同源物的翻译产物具有不同的催化性质。一些TaBx同源基因被高效转录，但翻译产物仅显示出弱的酶活性，这推断它们对Bx生物合成的贡献较弱。综合考虑转录水平和催化特性，我们得出结论，B基因组上的同源物通常对六倍体小麦中Bx的生物合成贡献最大，特别是在芽中。在四倍体小麦和六倍体小麦的三个二倍体祖先中，TaBx同源物的各自转录水平与在六倍体小麦中观察到的比例相似。这一结果表明，在六倍体小麦中TaBx基因转录的基因组偏好起源于
Hexaploid wheat (Triticum aestivum) accumulates benzoxazinones (Bxs) as defensive compounds. Previously, we found that five Bx biosynthetic genes, TaBx1-TaBx5, are located on each of the three genomes (A, B, and D) of hexaploid wheat. In this study, we isolated three homoeologous cDNAs of each TaBx gene to estimate the contribution of individual homoeologous TaBx genes to the biosynthesis of Bxs in hexaploid wheat. We analyzed their transcript levels by homoeolog- or genome-specific quantitative RTPCR and the catalytic properties of their translation products by kinetic analyses using recombinant TaBX enzymes. The three homoeologs were transcribed differentially, and the ratio of the individual homoeologous transcripts to total homoeologous transcripts also varied with the tissue, i.e., shoots or roots, as well as with the developmental stage. Moreover, the translation products of the three homoeologs had different catalytic properties. Some TaBx homoeologs were efficiently transcribed, but the translation products showed only weak enzymatic activities, which inferred their weak contribution to Bx biosynthesis. Considering the transcript levels and the catalytic properties collectively, we concluded that the homoeologs on the B genome generally contributed the most to the Bx biosynthesis in hexaploid wheat, especially in shoots. In tetraploid wheat and the three diploid progenitors of hexaploid wheat, the respective transcript levels of the TaBx homoeologs were similar in ratio to those observed in hexaploid wheat. This result indicates that the genomic bias in the transcription of the TaBx genes in hexaploid wheat originated