线虫转型发育和寄主识别的化学通讯研究进展

Abstract

线虫是一类低等无脊椎动物,在自然界分布很广。因为线虫通常生活在土壤或寄生物中,没有适宜的视觉或听觉系统,接收环境信号的重要途径就是借助于其精细的化学感受系统。研究表明,线虫能够通过识别挥发性物质来引导一系列行为:取食、交配、产卵和驱避有毒物质、避免高种群密度等。目前,对线虫化学感受机制的研究越来越被人们所重视,也取得了一些突破性进展。综合近年来已有的研究成果,从发育调控机制、寄主识别机制、化学感受机理等方面进行了详细系统的总结,并对未来研究和线虫防治进行了展望。;Nematodes are globally distributed invertebrates, which are often found living in soil or as parasites of animals, insects and plants. They lack vision and hearing systems, so the survival of both free-living and parasitic nematodes depends on well developed chemosensation and chemotaxis systems. Nematodes utilize chemical signals in their environment to detect food sources, potential hosts, noxious compounds, reproductive partners and sometimes to enable them to choose between alternative developmental states. Interest in the mechanisms involved in chemosensing and identification of the discrete components of the chemical signals has steadily increased over the past few decades. Here we have summarized and evaluated recent discoveries and advances in this field, involving the mechanism of developmental regulation, the recognition of hosts, the construction and function of the chemoreceptor system, signal transduction, the prospects for related research and the control of harmful nematodes based on chemical ecology. The pheromonal cues that indicate overcrowding, high temperature, or starvation can trigger the nematodes to enter into diapause and enhance longevity by modulating endocrine signaling and gene expression. The genetic and molecular basis of phenotypic plasticity has been studied extensively in <em>Caenorhabditis elegans</em>, and recently, it was discovered that pheromones called ascarosides secreted by <em>C. elegans</em> themselves induce formation of the dauer stage and the four chemoreceptors of the dauer juveniles. Recognition of hosts by nematodes is very specific and the chemical signals from the hosts, as well as the chemoreceptors of the nematodes play key roles in this process. Both free-living and parasitic nematodes can sense chemical signals comprised of water soluble and/or volatile compounds. The chemotaxis of <em>C. elegans </em>has been studied for over 30 years and inducing substances identified thus far include salt ion (Na⁺、Li⁺、Cl^-、OH^-), amino acid, nucleotides, biotin and some volatiles (pyrazine, diacetyl, benzaldehyde, 2,4,5-trimethylthiazole, isoamylalcohol, 2,3-pentanedione). Another example is <em>Bursaphelenchus xylophilus</em>, the pinewood nematode, which is a plant parasitic nematode that is transmitted via <em>Monochamus </em>beetles. The chemical relationships within this system has been under investigation for several years, but no conclusive results regarding the discrete signaling molecules involved and their roles within the system have been obtained to date. Electrophysiological analyses indicated that different responses to chemical signals are due to differences in the chemoreceptors of various species of nematodes, which are composed by amphid and phasmid. Specific chemoreceptors in the neurons recognize particular compounds, and the neurons work collectively to receive chemical signals, and then activate a response through signal transduction. Nematodes, especially plant parasitic nematodes, cause huge economic damages every year, as advances in the study of the chemosenation mechanism are made, more effective strategies based on chemical ecology may be devised, thus replacing traditional control methods utilized today.