Department of Metabolic Biology, John Innes Centre, Colney Lane, Norwich NR4 7UH, UK.
Plant J. 2011 Apr;66(1):66-79. doi: 10.1111/j.1365-313X.2011.04503.x.
Gene clusters for the synthesis of secondary metabolites are a common feature of microbial genomes. Well-known examples include clusters for the synthesis of antibiotics in actinomycetes, and also for the synthesis of antibiotics and toxins in filamentous fungi. Until recently it was thought that genes for plant metabolic pathways were not clustered, and this is certainly true in many cases; however, five plant secondary metabolic gene clusters have now been discovered, all of them implicated in synthesis of defence compounds. An obvious assumption might be that these eukaryotic gene clusters have arisen by horizontal gene transfer from microbes, but there is compelling evidence to indicate that this is not the case. This raises intriguing questions about how widespread such clusters are, what the significance of clustering is, why genes for some metabolic pathways are clustered and those for others are not, and how these clusters form. In answering these questions we may hope to learn more about mechanisms of genome plasticity and adaptive evolution in plants. It is noteworthy that for the five plant secondary metabolic gene clusters reported so far, the enzymes for the first committed steps all appear to have been recruited directly or indirectly from primary metabolic pathways involved in hormone synthesis. This may or may not turn out to be a common feature of plant secondary metabolic gene clusters as new clusters emerge.
基因簇是微生物基因组的一个常见特征，用于合成次生代谢产物。众所周知的例子包括放线菌中抗生素的合成基因簇，以及丝状真菌中抗生素和毒素的合成基因簇。直到最近，人们还认为植物代谢途径的基因没有聚类，而且在许多情况下确实如此；然而，现在已经发现了五个植物次生代谢基因簇，它们都与防御化合物的合成有关。一个显而易见的假设是，这些真核生物基因簇是通过水平基因转移从微生物中获得的，但有令人信服的证据表明事实并非如此。这就提出了一些有趣的问题，例如这些基因簇的广泛程度如何，聚类的意义是什么，为什么一些代谢途径的基因聚类而另一些不聚类，以及这些基因簇是如何形成的。在回答这些问题的过程中，我们可能希望更多地了解植物基因组可塑性和适应性进化的机制。值得注意的是，对于迄今为止报道的五个植物次生代谢基因簇，所有第一个关键步骤的酶似乎都直接或间接地从参与激素合成的初级代谢途径中招募而来。随着新基因簇的出现，这种情况是否会成为植物次生代谢基因簇的一个共同特征还有待观察。
