De Novo assembly and characterization of the transcriptome of susceptible and resistant rose species in response to powdery mildew

Abstract Powdery mildew caused by Podosphera pannosa was a major disease in cut and potted roses. There were some rose species represent resistance to powdery mildew, others have susceptibility. However, the unclear resistance/susceptibility mechanism of wild Rosa to powdery mildew and the lack of related resistant genes have been limiting the utilization of wild Rosa in the genetic improvement of modern rose cultivars. In this study, we sequenced and assembled the transcriptome of the susceptible Rosa gigantea and the resistant Rosa longicuspis using de novo sequence assembly. Aims of the study were to preliminarily revealed their PM resistance/susceptibility mechanisms and find several genes which play important roles in Rosa-powdery mildew pathogen interactions. Our results indicating that: (1) the active response to P. pannosa infection in R. gigantea (susceptible wild species) occurred later than that in R. longicuspis (highly resistant wild species), and their responses also differed; (2) the regulatory network of R. gigantea in response to P. pannosa infection was more complex and diverse than that of R. longicuspis; (3) find two MLO members RgMLO6 and RlMLO7 which likely play important roles in interaction of Rosa-powdery mildew pathogen. These results will provide us data support for the functional evolution of disease resistance/susceptibility genes. Furthermore, they will provide us new ideas and gene pool for breeding new varieties of powdery mildew resistant rose.

摘要 由蔷薇单囊壳菌（Podosphera pannosa）引起的白粉病是切花玫瑰和盆栽玫瑰的主要病害。有些蔷薇属植物表现出对白粉病的抗性，而有些则易感。然而，野生蔷薇对白粉病的抗性/易感机制不明确以及相关抗性基因的缺乏一直限制着野生蔷薇在现代月季品种遗传改良中的应用。在本研究中，我们利用从头测序组装技术对易感的大花香水月季（Rosa gigantea）和抗病的长尖叶蔷薇（Rosa longicuspis）的转录组进行了测序和组装。本研究的目的是初步揭示它们对白粉病的抗性/易感机制，并找到在蔷薇 - 白粉病病原菌相互作用中起重要作用的几个基因。我们的研究结果表明：（1）大花香水月季（易感野生种）对蔷薇单囊壳菌感染的积极响应比长尖叶蔷薇（高抗野生种）发生得晚，且它们的响应也不同；（2）大花香水月季应对蔷薇单囊壳菌感染的调控网络比长尖叶蔷薇更复杂多样；（3）发现了两个MLO成员RgMLO6和RlMLO7，它们可能在蔷薇 - 白粉病病原菌的相互作用中起重要作用。这些结果将为抗病/易感基因的功能进化提供数据支持。此外，它们将为培育抗白粉病月季新品种提供新思路和基因库。