印度梨型孢真菌促進小白菜生長的分子機制與生理研究

Abstract

印度梨型孢真菌（Piriformospora indica, P. indica）是一種新的根部內共生性真菌（root endophytic fungus），其屬於擔子菌門（Basidiomycota）中，蕈菌綱（Hymenomycetes）、絲核菌屬（Rhizoctonia）的真菌。根據前人報告，已知其對植物的生長發育有促進的作用，可使植物的生物量（biomass）增加，亦可使宿主植物對病原菌具抗性、抗氧化能力增强及讓植株有較高的耐旱、耐鹽性。本實驗以小白菜（Brassica campestris subsp. chinensis L.）為模式植物接種P. indica真菌，於感染7天後，植物側根、根毛發育較對照組旺盛；進而將植株栽種於盆中觀察，發現無論是地上部或是地下部組織，植物的鮮重皆明顯大於對照組。於分子層面研究中，從我們所建立的扣減式cDNA基因庫裡篩選到一群與植物生長素（auxin）相關的基因：分別是與促使細胞壁酸化（wall acidification）、與細胞間植物生長素運輸（auxin transport）及植物生長素訊息傳遞（auxin-signal transduction）相關的基因群。這些基因於被P. indica真菌感染的植株根部中，其相對表現量均有明顯提昇的情形；且於測量植物根部的植物生長素（auxin）含量，亦發現於實驗組樣品中植物生長素（auxin）濃度顯著的增加。將植物生長素輸入攜帶者（auxin influx carrier）－AUX1基因大量表現於阿拉伯芥植株中，初步觀察轉殖株植物之外表型發現，轉殖株有較龐大的根系組織，整株植物亦較野生對照組植株壯碩。綜合以上實驗結果，我們認為P. indica真菌感染宿主植物後，促進宿主植物生長發育，可能與促進植物體內植物生長素的新陳代謝（auxin metabolism）相關。

Piriformospora indica (P. indica) is a new root endophytic fungus. It belonged to the Hymenomycetes of the Basidiomycota. P. indica interacts with the roots of various mono- and dicotyledonous plants, showing a positive effect on biomass production. In addition to this growth promoting effect, P. indica also has the potential to induce resistance to fungal disease and to increase the antioxidative activities of plants. Further more, after the infection of P. indica, plant becomes more tolerance to salt and drought. In this study, we used a model plant, Chinese mustard (Brassica campestris subsp. chinensis L.), for infection with P. indica. After inoculation for 7 days, Chinese mustard increased the amounts of lateral roots and root hairs. The fresh weight of plants, including above ground and under ground parts, were raised and the biomass of whole plants also became bigger. Screening with a subtractive cDNA library, we obtained a group of auxin-related genes. They can be classified into three parts: The first is related to cell wall acidification; the second is about auxin transport and the third is about auxin-signal transduction. These genes were in large up-regulated in the infected plant root. Moreover, the accumulated concentration of auxin in infected plant roots was higher than that in control plants. A transgenic Arabidopsis plant which has AUX1 gene-over expression was created. The transgenic plants have highly branched root systems and greater biomass than the wild type plants. We propose that the growth-promoting effect caused by P. indica is correlated with auxin metabolism.