| Summary: | 博士 === 國立中興大學 === 昆蟲學系所 === 96 === Investigations on taxonomic position and phylogeny of the yeast-like symbiote (YLS) in Delphacidae (Insecta: Hemiptera) were carried out using paraffin sectioning and analyses of uricase gene sequences in the brown planthopper, Nilaparvata lugens. Uricase gene was known to be present in the YLS of the planthoppers (Hemiptera: Delphacidae). Based on uricase gene sequences, the YLS of Delphacidae belongs to Ascomycota in Fungi, and forms a monophylic group. By phylogenetic analysis, coevolutionary relationship between YLS and Delphacidae hosts was suggested, whereas the relationship among the symbiotes of their host insects from the same host plant was placed the same clade. By in situ hybridization, except compound eye and muscle, uricase gene was found in most body cavity, especially abundant in fat body syncytia and also in ovaries and oviposotional tubes. Real-time PCR analyses of the YLS uricase DNA levels and mRNA transcriptions in different developmental stages of N. lugens showed that the uricese DNA was more abundant in adult females than in adult males and the mRNA was declined in the older nymphal stages. After heat treatment at 35oC, the transcription of uricase mRNA was lower in the heat-treated insects than those incubated at room temperature for 24 h. However, the mRNA was restored to the normal level after heat treatment for 48 and 72 h. These results indicated that heat treatment could reduce the activity of YLS uricase gene. The YLS had coevolutionary relationship with Delphicidae hosts based on uricase gene sequence analyses. The DNA and mRNA transcriptions of uricase gene were age dependent, and reduced by heat treatment at 35oC.
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