叶极性基因ARF4的进化

Exploring the evolution of genes related to development possibly makes us further understand the origin of morphological diversity. People have recovered the association between leaf origin and HD-ZIPIII,a leaf polarity gene which specifies the morpholgy of adaxial domain of leaf blades. The Arabidopsis leaf polarity gene ARF4 determines the morphology of abaxial domain of leaf blades, and locates itself at unique signaling pathway. ARF4 possibly emerges after the landing of green plants, and bryophytes possess extremely similar sequences. Thus, it is distinctive and practicable to study the evolution of ARF4 in order to deepen the insight into leaf origin. This project would as possible clone ARF4 orthologs and paralogs from each major group of land plants in order to obtain complete and solid ARF4 phylogeny, then first and foremost in representative species establish for these genes the expression pattern in leaf primordia - - - not expressing in adaxial domain of leaves but doing in their abaxial domains or other pattern, supplemented with studying gene duplication and natural selection, and ultimately resolve to certain extent the scientific complex of the relationship between ARF4 and leaf origin. This research would at the first time prove the multiple origin of ferns leaves and the co-evolution between leaf polarity genes, simultaneously further prove other judgements such as the enation theory on the nature of lycophytes leaves and the theory of the common origin of seed plants leaves, and strengthen the research of leaf evodevotics.

研究发育相关基因的进化也许能使我们进一步了解形态多样性的起源。人们已发现了决定叶片上部分形态的叶极性基因HD-ZIPIII与叶起源的联系。拟南芥的叶极性基因ARF4决定叶片的下部分形态，并处于独特的信号通路。ARF4可能产生于绿色植物登陆之后，苔藓植物有与其非常相似的序列。因此，研究ARF4的进化以加深对叶起源的认识是有特色和可操作的。本项目拟从各个陆地植物大类群尽可能地克隆ARF4的直系和旁系同源基因以获得全面和可靠的ARF4系统发育关系，然后重点明确代表性物种中ARF4同源基因在叶原基中的表达模式- - 在叶的上部分不表达而在其下部分表达或其它模式，辅以研究基因重复和自然选择，最终在一定程度上解决ARF4与叶起源的关系这个科学问题。该研究有可能首次证明蕨类植物叶的多次起源以及叶极性基因的共进化，同时进一步证明石松类植物叶本质的突出学说和种子植物叶的共同起源学说，并强化叶进化发育遗传学研究。

鉴于叶的多次起源假说的功能基因方面的证据较少，本项目研究了叶极性基因ARF4的进化。首先，本项目针对蕨类植物的叶发育，对粗梗水蕨的两个样品、贵州贯众和中日金星蕨各一个样品进行了转录组测序，分别产生了11.6、12.3、13.3和13.3 Gb的干净数据，并结合RT-PCR获得了这三个物种的ARF4基因的完整编码区。ARF家族的三个分支ARF5/6、ARF10和ARF2/4可能都参与了蕨类植物的叶发育。蕨类植物中已分化出ARF2和ARF4亚支，并且前者为多拷贝而后者为单拷贝。ARF4在种子植物的共同祖先以及被子植物的共同祖先里都发生了一次基因重复。蕨类植物的ARF4基因可能拥有一个tasiR-ARF结合位点，而裸子植物的ARF4有的有两个有的只有一个这样的位点，同时被子植物的ARF4均有两个这样的位点。蕨类植物与种子植物一样拥有两类产生tasiR-ARF的TAS3基因。对粗梗水蕨的两个样品的小RNA测序发现了284个已知类型的miRNA和173个全新的miRNA，特别是找到了加工TAS3的miR390以及匹配tasiR-ARF的小RNA。粗梗水蕨的ARF2基因可能受到了tasiR-ARF的切割，但tasiR-ARF是否切割ARF4尚不明确。粗梗水蕨的ARF4在叶背部的孢子囊部位表达。所以，蕨类植物ARF4基因的序列和表达模式倾向于石松类植物小型叶、蕨类植物的叶以及种子植物叶均为独立起源的观点。