長葉木薑子蟲癭轉錄體之研究

Abstract

蟲癭（insect gall）是植物經過造癭昆蟲刺激後產生不正常增生組織。至今蟲癭的形成機制仍不明瞭。先前研究著重於分類學、動物學、生態學等，隨著次世代定序發展，使得探討基因表現等轉錄體研究也越快捷。本論文研究長葉木薑子（Litsea acuminata）蟲癭之轉錄體，以了解蟲癭的形成發育機制。研究蟲癭與其宿主葉基因表現差異，一共發現1,452個差異表現基因，其中包含細胞壁、植物激素代謝、植物逆境、光合作用、二次代謝、四吡咯生合成等類群。資料顯示蟲癭組織光合作用相關基因表現量降低，推測蟲癭組織無法提供足夠養分構築蟲癭結構或是提供造癭昆蟲，營養則可能由宿主葉而來，進而顯示植物組織從葉片轉變成蟲癭組織是一種營養流的改變，即從供源（source）轉變成積儲（sink）。本研究還發細胞壁相關基因表現上升，以及植物激素如油菜素類固醇、生長素與吉貝素相關基因表現上升，並推測上述幾種植物激素在蟲癭形成中可能扮演重要角色。造癭昆蟲不但誘導蟲癭構形還啟動植物防禦系統，如致病過程相關蛋白質（pathogenesis-related proteins, PR protein）基因表現上升，此可能誘發植物系統性誘導抗病機制（systemic acquired resistance）以阻礙病原侵入。Insect galls are the abnormal growth of plant tissue induced by herbivore, bite or egg laying from insects. To date, the mechanisms of gall formation are still undetermined. Previous researches used taxonomical, zoological and ecological approaches to study insect galls. In this study the insect galls were investigated with the view of transcriptome. We collected cup-shaped galls on host leaves of Litsea acuminata, and characterized the differential gene expression between galls and its host leaves by using next generation sequencing and transcriptomic approaches. A total of 1,452 differentially expressed genes (DEGs) were found between insect gall and it host leaf. These DEGs are classified into functional category of cell wall, hormone metabolism, abiotic or biotic stress, photosynthesis, secondary metabolism, tetrapyrrole synthesis and so on. The data showed that the gall shift from a source (host leaves) to a sink (gall tissues) with decreased gene expression of photosynthetic-related genes. I also analyzed the cell wall synthesis and plant hormone like brassinosteroids, auxin and gibberellin. These hormones may play important role in gall development. Insects not only induce the structure of galls but also stimulate plant defense system. For example that increased expression of genes related to pathogenesis-related proteins (PR protein). They are induced as part of systemic acquired resistance (SAR) to resist disease.