SAP54AY 效應蛋白質誘導花器葉化之電顯觀察

Abstract

中文摘要 翠菊黃萎病植物菌質體(Aster yellows witches'-broom, AYWB)是一種由昆蟲傳播的植物病原，罹病植株表現簇葉、花器綠化及花器葉化等病徵。翠菊黃萎病植物菌質體的分泌蛋白中，辨識出56條AY-WB 蛋白 (SAPs)，並建立穩定的轉基因阿拉伯芥品系。其中SAP54效應蛋白會調控SAP54轉基因阿拉伯芥表現出花器葉化。SAP54轉基因阿拉伯芥的花器分為三型；第一型為花器部分葉化，但仍保有白色花瓣。第二型表現出花器葉化、綠化，並有數個葉化花芽。第三型花器明顯葉化、綠化，其萼片擴大、形似葉片。本研究利用掃描式電子顯微鏡觀察SAP54轉基因阿拉伯芥。第一型花器產生了額外的花序及毛狀體，細胞大致排列緊密，但形狀不規則。第二型花器從原本主花的雌蕊處產生了許多簇生花亦產生了毛狀體。細胞形狀變得更不規則，且有部分細胞融合。第三型花器的花瓣及萼片變的極似葉片也都在表面產生了毛狀體。細胞呈現大、形狀不規則，且表面光滑；同一片花瓣從邊緣到中心部，葉化趨勢漸趨明顯，花瓣邊緣的細胞小、葉化較不明顯，靠近花瓣中心的細胞較大且葉化。上述結果表示SAP54影響阿拉伯芥花器發育的基因表現。

Abstract Aster yellows witches’-broom (AYWB) phytoplasma is an insect-transmitted plant pathogen that induces various symptoms, including witches’-broom, virescene and phyllody (leafy flower) in the infected plants. Bai et al. (2009) identified 56 secreted AY-WB proteins (SAPs) and created stable transgenic Arabidopsis lines. In addition, MacLean et al. (2011) identified SAP54 effector, which mediates leafy flower in Arabidopsis SAP54 plants. The floral morphology of SAP54 plants were classified into three Types. Type 1 showed partial phyllody with white petals. Type 2 showed phyllody and virescence with multiple leafy flower buds. Type 3 showed phyllody, virescence, and enlarged leaf-like sepals. In this study, we observed the leafy flower phenotypes on SAP54 plants by scanning electron microscopy (SEM). Results showed that the Type 1 flower produced additional inflorescences and trichomes, cells were arranged approximately in an order with less regular shape. Type 2 leafy flower had multiple flower appeared from the position of pistal in the primary flower and trichomes were seen. Cells became more irregular in shape and some cells seem to be merging. Type 3 flower’s sepals and petals became very leaf-like and both appeared trichomes on their surface. Cells showed irregular cells with large size and smooth surface. Moreover, the conversion of regular cells to leafy flower cells proceeded progressively from the central portion towards the edge portion, resulting elongated cells in the central part and small cells near the edge. These results suggest that SAP54 alters the gene expression on floral organ development.