Three genomes differentially contribute to the biosynthesis of benzoxazinones in hexaploid wheat. Proc Natl Acad Sci USA

Divisions of Applied Biosciences and Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 12/2005; 102(45):16490-5. DOI: 10.1073/pnas.0505156102
Source: PubMed


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 RT-PCR 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 in the diploid progenitors and has been retained through the polyploidization.

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    • "As from the hexaploid wheat ' Chinese Spring ' and the 2BS . 2RL wheat - rye translocation , the expression of some of the transcripts was found to be significantly higher or lower in the hexaploid wheat than in the diploid progenitor . Unequal expression of homoeologous genes and changes in homoeolog bias have been observed in polyploid species ( Nomura et al . , 2005 ; Hovav et al . , 2008 ) . We can speculate that some specific genome pref - erential transcripts exhibit expression changes in hexaploid wheat including chromosome translocation lines . The target genomic region for over two thousand tran - scripts that were identified as preferentially hybridizing either ' Chinese Spring ' or 2BS . 2R"
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    ABSTRACT: Wheat-rye translocations are widely used in wheat breeding to confer resistance against abiotic and biotic stress. Studying gene expression in wheat-rye translocations is complicated due to the presence of homoeologous genes in hexaploid wheat and high levels of synteny between wheat and rye chromatin. To distinguish transcripts expressed from each of the three wheat genomes and those from rye chromatin, genomic probes generated from diploid progenitors of wheat and rye were synthesized on a custom array. A total of 407 transcripts showed homoeologous genome (‘A’, ‘B’ or ‘D’ genome)- or rye genome (‘R’)-specific differential expression, based on unequal values of probe hybridization. In a 2BS.2RL wheat-rye translocation, thirteen of the 407 transcripts showed preferential expressions from rye chromatin. As well as quantifying variation in homoeologous transcript in wheat-rye translocations, this study also provides a potential aid to examine the contribution of the subgenomes to complex allohexapolyploids.
    Genes & Genetic Systems 02/2015; 89(4):159-168. DOI:10.1266/ggs.89.159 · 0.93 Impact Factor
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    • "As common wheat is hexaploid (2n = 42) that contains three subgenomes, namely A, B, and D; and seven pairs of homoeologous chromosomes per subgenome, each gene has three copies. Previous studies have shown that the genomic contributions to the total expression of a target gene vary with tissues and developmental stages (Nomura et al., 2005; Deol et al., 2013). Therefore, identifying and characterizing the homoeologs of a candidate gene from each of the three genomes, and elucidating the degree of their contributions to the total expression of a target gene are important for detailed dissection of the underlying molecular mechanisms regulating seed dormancy. "
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    Frontiers in Plant Science 09/2014; 5:458. DOI:10.3389/fpls.2014.00458 · 3.95 Impact Factor
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    • "Several studies on the differential expression of homoeoloci in wheat have focussed on the expression of a relatively small number of genes [46-48,61,71]. Subsequent genome-wide assessments have so far used microarrays, which are difficult to interpret for the expression of closely related genes [42-45]. "
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