植物Tm-1-like基因的起源和进化分析

发布时间：2018-06-10 00:52

本文选题：Tm-1-like(Tm-1L)基因 + 水平基因转移　；参考：《扬州大学》2017年硕士论文

【摘要】：陆生植物的起源是地球生命进化史上的最为重要的事件之一,对现代陆地生态系统的形成具有至关重要的作用。陆生植物起源于水生的绿藻,在由水生到陆生的进化过程中,陆生植物祖先面临着干旱、多变的温度、增强的紫外线辐射等诸多不利因素,此外陆生植物还要面对与水生环境截然不同的微生物环境,因此,植物在登陆陆地的过程中需要进化出新的基因和新表型特征来适应陆地的生存环境。番茄(Solanum lycopersium L.)的Tm-1基因是番茄花叶病毒(Tomatomosaic virus,ToMV)的重要抗性基因,其抗性等位基因来源于野生番茄(S.habrochaite)。Tm-1基因编码的蛋白质序列与已知抗性基因(R gene)具有截然不同的序列特征,该基因编码的蛋白质能特异地结合ToMV的复制蛋白并对RNA复制起到抑制作用,从而表现出对番茄花叶病毒的抗性。对该基因的序列相似性分析发现其在已测序陆生植物基因组中普遍存在同源基因,并表现出高度的序列保守性。该基因在植物中的同源基因编码的蛋白质具有相似的结构域特征,其N-末端均具有UPF0261结构域,而C-末端均具有TBST结构域。尽管该基因在番茄中的抗病作用已经明确,但其起源和进化模式还不清楚,尤其是其在其他植物中的功能尚有待进一步挖掘。本文基于生物信息学方法,采用序列相似性和系统进化树相结合的方法揭示植物Tm-1-like(Tm-1L)基因的起源机制;进一步在玉米中通过RT-PCR方法分析该基因的组织器官和非生物逆境表达模式。研究结果将为揭示植物Tm-1L基因的起源和进化模式,并为在其他植物物种中对该基因开展功能鉴定提供借鉴。主要研究内容和结果包括:(1)序列相似性分析发现已测序的链形植物(包括陆生植物和轮藻)中均具有Tm-1L基因,并且序列具有高度保守的特征,而在链形植物的祖先物种绿藻和红藻中却没有同源基因。(2)植物Tm-1L基因编码的蛋白质序列中具有2个高度保守的结构域:N-末端为UPF0261 结构域,C-末端是TIM-barrel-like signal transduction(TBST)结构域。进一步分析发现同时编码这2个结构域的基因仅在链形植物中出现,而其他物种中的同源基因仅仅编码其中1个结构域的蛋白质序列。(3)分别以包含UPF0261和TBST结构域的代表性蛋白质序列构建了系统进化树,结果发现植物编码UPF0261结构域的基因和编码TBST结构域的基因是通过2次不同的水平基因转移(horizontal gene transfer,HGT)事件起源的,其中UPF0261基因的假定供体是细菌,而TBST基因的假定供体是真菌或原核生物。植物中具有UPF061和TBST结构域的蛋白质序列被同一基因编码,可能是这2个基因之间的一次基因融合(gene fusion)的结果。(4)对UPF0261和TBST蛋白质序列进行了共进化(co-evolution)分析,结果发现在真菌、细菌和古菌中UPF0261和TBST蛋白质之间均存在明显的共进化特征,表明UPF0261和TBST基因之间可能具有功能的互补性,并存在交互作用。(5)基于对植物Tm-1L基因的起源和进化分析,本文提出了一种新的基因起源机制,即:存在交互作用的多个基因可以通过多次独立的水平基因转移事件进入受体基因组,进一步在受体基因组中通过基因融合形成一个基因,并行使功能。(6)为初步揭示该基因在玉米中的潜在功能,本研究分别在苗期和抽雄期对该基因的组织表达模式进行了分析,结果发现苗期该基因在幼茎中表达量最高,而抽雄期则在雌穗中表达量最高。(7)进一步分析了玉米Tm-1L基因在非生物逆境条件下的表达模式,结果发现该基因在干旱、低温、高温和高盐等非生物逆境胁迫下,表达量显著增强。此外,该基因的表达还受到ABA的诱导。研究结果表明该基因可能参与植物对非生物逆境胁迫的响应。
[Abstract]:The origin of terrestrial plants is one of the most important events in the history of life evolution of the earth. It plays a vital role in the formation of modern terrestrial ecosystems. The terrestrial plants originated from aquatic green algae. In the process of evolution from aquatic to terrestrial, the ancestors of terrestrial plants faced drought, variable temperature, enhanced ultraviolet radiation and so on. In addition, the terrestrial plants need to face a different microbial environment which is completely different from the aquatic environment. Therefore, the plants need to evolve new genes and new phenotypic characteristics to adapt to the terrestrial environment in the process of landing land. The Tm-1 gene of Solanum lycopersium L. is Tomatomosaic virus, ToMV The genes encoded by the wild tomato (S.habrochaite).Tm-1 gene and the known resistance gene (R gene) have distinct sequence characteristics. The protein encoded by this gene can specifically bind the replicating egg white of ToMV and inhibit the replication of RNA, thus showing the opposite effect. Resistance of eggplant mosaic virus. The sequence similarity analysis of the gene found that the homologous genes existed in the genome of the sequenced terrestrial plants and showed a high sequence conservatism. The gene encoded by homologous genes in the plant had similar domain characteristics, and the N- end of the gene had a UPF0261 domain, and the end of C- was the end of the gene. All of them have TBST domain. Although the resistance of the gene is clear in tomato, its origin and evolution model is not clear, especially its function in other plants remains to be further excavated. Based on the bioinformatics method, the combination of sequence similarity and phylogenetic tree is used to reveal plant Tm-1-like (T). M-1L) the mechanism of gene origin; further analysis of the gene organ and abiotic stress expression pattern in Maize by RT-PCR method. The results will reveal the origin and evolution pattern of the plant Tm-1L gene and provide reference for the functional identification of the gene in other plant species. The main contents and results include the main contents and results. (1) sequence similarity analysis found that the sequenced chain plants (including terrestrial plants and algae) have Tm-1L gene, and the sequence is highly conserved, but there are no homologous genes in the ancestral species of the chain plant green algae and red algae. (2) the protein sequences encoded by the plant Tm-1L gene have 2 highly conserved structures. Domain: the N- end is the UPF0261 domain, and the end of the C- is the TIM-barrel-like signal transduction (TBST) domain. Further analysis shows that the genes encoding the 2 domains are found only in the chain plants, and the homologous genes in other species only encode the protein sequences of the 1 domains. (3) include UPF0261 and TBST nodes, respectively. The representative protein sequence of the domain constructs the phylogenetic tree. The results show that the gene and the gene encoding the TBST domain of the UPF0261 domain are derived from the 2 different horizontal gene transfer (horizontal gene transfer, HGT), in which the UPF0261 gene assumes that the donor is a bacterium, and the presumed donor of the TBST gene is the donor. Fungi or prokaryotes. Protein sequences with UPF061 and TBST domains in plants are encoded by the same gene, which may be the result of one gene fusion (gene fusion) between the 2 genes. (4) the sequence of UPF0261 and TBST proteins was coevolved (co-evolution), and the results were found in fungi, bacteria and paleo bacteria in UPF0261 and TBST. There are obvious coevolution characteristics between proteins, indicating that the UPF0261 and TBST genes may have functional complementarity and interaction. (5) based on the analysis of the origin and evolution of plant Tm-1L genes, this paper proposes a new gene origin mechanism, that is, multiple genes stored in interaction can be independent by many times. The horizontal gene transfer event enters the receptor genome, further forms a gene through gene fusion in the receptor genome, and exercises its function. (6) the potential function of the gene in maize is preliminarily revealed. This study analyzed the pattern of the gene in the seedling stage and the male stage, and the results were found at the seedling stage. The expression of the young stem was the highest, while the male stage was the highest in the female ear. (7) the expression pattern of the maize Tm-1L gene under abiotic stress was further analyzed. The results showed that the gene was significantly increased under the abiotic stress of drought, low temperature, high temperature and high salt. In addition, the expression of the gene was also induced by ABA. The results suggest that the gene may be involved in the response of plants to abiotic stress.
【学位授予单位】：扬州大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：Q943.2

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