Lohtander Katileena, Pasonen Hanna-Leena, Aalto Markku K, Palva Tapio, Pappinen Ari, Rikkinen Jouko
Botanical Museum, P.O. Box 7, 00014 University of Helsinki, Finland.
Environ Biosafety Res. 2008 Oct-Dec;7(4):227-39. doi: 10.1051/ebr:2008019. Epub 2008 Oct 29.
Chitinases are hydrolytic enzymes that have been employed in biotechnology in attempts to increase plants' resistance against fungal pathogens. Genetically modified plants have given rise to concerns of the spreading of transgenes into the environment through vertical or horizontal gene transfer (HGT). In this study, chitinase-like sequences from silver birch (Betula pendula) EST-libraries were identified and their phylogenetic relationships to other chitinases were studied. Phylogenetic analyses were used to estimate the frequency of historical gene transfer events of chitinase genes between plants and other organisms, and the usefulness of phylogenetic analyses as a source of information for the risk assessment of transgenic silver birch carrying a sugar beet chitinase IV gene was evaluated. Thirteen partial chitinase-like sequences, with an approximate length of 600 bp, were obtained from the EST-libraries. The sequences belonged to five chitinase classes. Some bacterial chitinases from Streptomyces and Burkholderia, as well as a chitinase from an oomycete, Phytophthora infestans, grouped together with the class IV chitinases of plants, supporting the hypothesis that some class IV chitinases in bacteria have evolved from eukaryotic chitinases via horizontal gene transfer. According to our analyses, HGT of a chitinase IV gene from eukaryotes to bacteria has presumably occurred only once. Based on this, the likelihood for the HGT of chitinase IV gene from transgenic birch to other organisms is extremely low. However, as risk is a function of both the likelihood and consequences of an event, the effects of rare HGT event(s) will finally determine the level of the risk.
几丁质酶是水解酶，已被应用于生物技术领域，旨在增强植物对真菌病原体的抗性。转基因植物引发了人们对转基因通过垂直或水平基因转移（HGT）扩散到环境中的担忧。在本研究中，从银桦（Betula pendula）EST文库中鉴定出几丁质酶样序列，并研究了它们与其他几丁质酶的系统发育关系。系统发育分析用于估计植物与其他生物之间几丁质酶基因历史基因转移事件的频率，并评估系统发育分析作为携带甜菜几丁质酶IV基因的转基因银桦风险评估信息来源的有用性。从EST文库中获得了13个长度约为600 bp的部分几丁质酶样序列。这些序列属于五个几丁质酶类别。一些来自链霉菌和伯克霍尔德菌的细菌几丁质酶，以及来自卵菌疫霉（Phytophthora infestans）的一种几丁质酶，与植物的IV类几丁质酶聚集在一起，支持了细菌中的一些IV类几丁质酶是通过水平基因转移从真核几丁质酶进化而来的假说。根据我们的分析，几丁质酶IV基因从真核生物到细菌的水平基因转移可能仅发生过一次。基于此，几丁质酶IV基因从转基因桦树转移到其他生物的可能性极低。然而，由于风险是事件可能性和后果的函数，罕见水平基因转移事件的影响最终将决定风险水平。
