石斛小菇促进天麻种子萌发的转录组研究

RNA-Seq analysis of Gastrodia elata seed germination infected with Mycena dendrobii

天麻Gastrodia elata种子细小而无胚乳,自然条件下需要石斛小菇Mycena dendrobii等真菌共生来完成种子萌发和生长。为了探讨天麻种子接菌萌发过程中的基因表达变化,本研究利用高通量RNA测序技术,对共生真菌石斛小菇、天麻成熟种子以及接菌萌发后的天麻原球茎进行比较分析,共获得42 263条注释unigenes,并筛选到5 409条差异表达基因。GO分析表明,差异表达基因主要参与代谢、离子结合等生物学通路中。KEGG功能富集分析结果表明,差异基因参与了植物激素信号传导、碳代谢、苯丙素生物合成、淀粉与蔗糖代谢以及氨基酸生物合成中。真菌和植物细胞壁多糖经降解产生的寡糖激发子,可以诱导宿主产生多种防御反应,参与到宿主与真菌互作中。在共生萌发过程中,真菌细胞壁降解相关基因的表达显著提高,如几丁质酶和β‐1,3‐葡聚糖酶基因表达甚至上调了20倍之多。此外,植物细胞壁木聚糖酶和果胶酶基因表达显著升高。这类基因表达可释放寡糖激发子,在天麻种子对石斛小菇的防御过程中起到重要的作用。本文全面分析天麻种子接菌萌发前后基因表达变化,为进一步研究天麻重要功能基因的功能鉴定提供基础。

In nature, orchid seeds possess no endosperm and therefore are devoid of nutrient supply. Mycorrhizal fungi （e.g., Mycena dendrobii） can provide the orchid seeds with signals and nutrients for germination. The mature seeds and protocorms of Gastrodia elata, and the hyphae of M. dendrobii were sequenced by using RNA-seq platform to elucidate the changes of gene expression in G. elata. All unigenes were searched against seven public databases and 42 263 unigenes were annotated in at least one database. We analyzed 5 409 differentially expressed unigenes through clustering and functional enrichment. Based on GO analysis, most genes were classified as the functors involving metabolism, signal transduction, and binding. KEGG analysis results indicated that the differentially expressed genes participated in translation, carbohydrate metabolism, signal transduction, plant hormone signal transduction, carbon metabolism, phenylpropanoid biosynthesis, starch and sucrose metabolism, and phenylalanine metabolism. The hydrolase genes that act on the cell walls of fungi or plants, such as chitinase, β-glucanase, xylanase and pectinase, showed higher expression in protocorms than in mature seeds. The oligosaccharide elicitors were released from cell walls. Our results indicated that the accumulation of elicitors may play important roles in the defense mechanism when the seeds infected by symbiotic fungi.