最新Nature公布两大基因组测序结果

　　生物通报道：6月11日的Nature杂志公布了两项重要的基因组测序结果：巨桉树基因组，以及栉水母“太平洋侧腕水母”的基因组，这些遗传信息的解析将有助于我们更深入的了解生物功能基因变异，以及相关经济产物的作用机理。

来自佛罗里达大学的研究人员发表了栉水母“太平洋侧腕水母”(Pleurobrachia bachei)的基因组草图以及另外其他十种栉水母的转录组。从中研究人员发现这种生物基因组序列省略了在所有其他动物中都有的基因种类，包括有关免疫、发育和神经功能的正常基因。针对这种情况，研究人员认为栉水母进化出了一个独立的神经系统。

栉水母一直令分类学家们头疼不已。它们和水母看起来很相似，曾经被视为刺胞动物（包括水母）的姐妹群(Sister group)。也有人将栉水母放在缺乏神经系统的扁盘动物和海绵之后，因为栉水母具有能够检测光、感知猎物和移动肌肉组织的神经系统。

在这项研究中，研究人员发现这些基因组的神经、免疫和发育基因含量与其他动物基因组显著不同，比如说没有HOX基因和标准的微RNA机制，免疫基因补充也减少了。而且很多双侧神经元特定基因和“经典”神经传输物通道的基因在神经元中不存在或没有表达。由此研究人员提出，栉水母的神经系统(还可能包括肌肉分化)是独立于其他动物的方式演化的。

神经系统在不同动物分支中演化两次，不过这项研究并不认同Moroz等人给栉水母安排的进化位置，而是认为所有动物的共同祖先可能与栉水母没什么关系。

另外一项研究（The genome of Eucalyptus grandis），由南非比勒陀利亚大学领导的一个研究组公布了首个双子叶植物纲桃金娘目巨桉树参考基因组。这一基因组大小为640兆碱基，从中研究人员预测了36,376个蛋白质编码基因，其中三分之一存在串联重复。

“这是迄今为止在植物基因组中发现的最大比例的串联重复”，研究人员在文中写道。研究人员还发现了一些特殊代谢产物的基因，这些代谢产物在巨桉树的防御功能中扮演了重要角色，并且也参与了目前被用于多个不同行业的精油的生成过程。

“未来功能基因变异方面的研究将能进一步解析桉树进化过程中漂移和选择的相对影响，同时也有助于揭示这种植物物种形成和适应性分支（adaptive divergence,生物通译）的机制，”来自比勒陀利亚大学的Zander Myburg表示，“这些新知也能促进我们对桉树如何对环境变化作出应对的理解。”

（生物通：万纹）

原文摘要：

The genome of Eucalyptus grandis

Eucalypts are the world’s most widely planted hardwood trees. Their outstanding diversity, adaptability and growth have made them a global renewable resource of fibre and energy. We sequenced and assembled >94% of the 640-megabase genome of Eucalyptus grandis. Of 36,376 predicted protein-coding genes, 34% occur in tandem duplications, the largest proportion thus far in plant genomes. Eucalyptus also shows the highest diversity of genes for specialized metabolites such as terpenes that act as chemical defence and provide unique pharmaceutical oils. Genome sequencing of the E. grandis sister species E. globulus and a set of inbred E. grandis tree genomes reveals dynamic genome evolution and hotspots of inbreeding depression. The E. grandis genome is the first reference for the eudicot order Myrtales and is placed here sister to the eurosids. This resource expands our understanding of the unique biology of large woody perennials and provides a powerful tool to accelerate comparative biology, breeding and biotechnology.

The ctenophore genome and the evolutionary origins of neural systems

The origins of neural systems remain unresolved. In contrast to other basal metazoans, ctenophores (comb jellies) have both complex nervous and mesoderm-derived muscular systems. These holoplanktonic predators also have sophisticated ciliated locomotion, behaviour and distinct development. Here we present the draft genome of Pleurobrachia bachei, Pacific sea gooseberry, together with ten other ctenophore transcriptomes, and show that they are remarkably distinct from other animal genomes in their content of neurogenic, immune and developmental genes. Our integrative analyses place Ctenophora as the earliest lineage within Metazoa. This hypothesis is supported by comparative analysis of multiple gene families, including the apparent absence of HOX genes, canonical microRNA machinery, and reduced immune complement in ctenophores. Although two distinct nervous systems are well recognized in ctenophores, many bilaterian neuron-specific genes and genes of ‘classical’ neurotransmitter pathways either are absent or, if present, are not expressed in neurons. Our metabolomic and physiological data are consistent with the hypothesis that ctenophore neural systems, and possibly muscle specification, evolved independently from those in other animals.