促生解淀粉芽胞杆菌SQR9定殖对黄瓜根系基因表达的转录组学研究

Transcriptomic analysis of colonization by plant growth-promoting rhizobacterium Bacillus amyloliquefaciens SQR9 on gene expression of cucumber roots

[目的]本文旨在阐明黄瓜植株接种促生解淀粉芽胞杆菌SQR9后其根系基因的表达谱变化特征,从植物响应微生物的角度揭示植物根际促生细菌(plant growth-promoting rhizobacteria,PGPR)的作用机制。[方法]利用Illumina高通量测序技术研究接种菌株SQR9对黄瓜根系基因表达谱影响的转录组特征,对显著差异表达基因进行GO功能和KEGG富集分析。[结果]与未接种的对照黄瓜植株比较,菌株SQR9接种72 h后黄瓜根系有484个基因的表达发生显著变化,包括300个上调基因和184个下调基因。Real-time PCR验证表明基因表达差异趋势与转录组测序结果一致,证明测序结果可信。黄瓜根系响应菌株SQR9的差异基因主要参与碳水化合物代谢、氨基酸代谢、次级化合物代谢和信号转导途径等。在植物促生方面,氨基酸代谢途径中ASP1基因(编码天冬氨酸转氨酶)表达上调约4倍;糖酵解途径中PDC基因(编码丙酮酸脱羧酶)和卡尔文循环中FBA6基因(编码果糖二磷酸醛缩酶)表达均上调3~5倍;生长素响应途径中编码生长素抑制子的IAA8基因表达显著下调,而编码响应蛋白的基因SAUR77和SAUR21表达均上调3倍左右,表明菌株SQR9产生的外源吲哚乙酸(indole-3-acetic acid,IAA)激活了植物内源的IAA信号途径。在植物免疫方面,免疫信号途径转录因子的编码基因WRKY29和ERF1B表达上调,激活植物系统抗性并有助于提高抗病能力;编码抗胁迫因子的C_(4)H和ADH1基因表达也显著上调,提高植物抗逆能力。[结论]菌株SQR9可通过调控黄瓜根系代谢相关基因表达和激活免疫途径相关基因的方式促进黄瓜植株生长并提高其抗病能力。

[Objectives]The objective of this study was to illustrate the plant growth-promoting mechanisms in terms of the response of plants to rhizosphere beneficial microbes,based on the transcriptional profiling of cucumber root genes responsive to the inoculation of plant growth-promoting rhizobacterium Bacillus amyloliquefaciens SQR9.[Methods]The transcriptional response of cucumber root genes to B.amyloliquefaciens SQR9 was analyzed by Illumina high-throughput transcriptome sequencing;the significant differentially expressed genes were further examined by gene ontology(GO)and Kyoto encyclopedia of genes and genomes(KEGG)analysis.[Results]As compared with the non-inoculated control,484 genes were detected to be significantly differentially expressed after the inoculation of strain SQR9,including 300 up-regulated genes and 184 down-regulated genes.Real-time PCR validation showed that the expression patterns of the selected genes were in accordance with the results of transcriptional profiling analysis,suggesting that the transcriptome data were reliable.The differentially expressed genes in response to strain SQR9 were mainly involved in carbohydrate metabolism,amino acid metabolism,biosynthesis of other secondary metabolites,and signal transduction.With regards to the genes related to plant growth-promotion,ASP1 that encodes for an aspartate transaminase was activated by strain SQR9 and was up-regulated by approximately 4 times;the expression of PDC encoding for pyruvate decarboxylase in glycolysis(EMP pathway),as well as FBA6 encoding for fructose-bisphosphate aldolase in Calvin cycle,were both up-regulated by 3-5 times in the inoculated treatment as compared with the control;in the IAA-responsive pathway,IAA8 that encodes for a repressor,was down-regulated by strain SQR9,while SAUR77 and SAUR21 encoding the responsive proteins,were up-regulated by approximately 3 times,suggesting that the exogenous indole-3-acetic acid(IAA)stimulated the endogenesis IAA-pathway in plants.In regard to plant immunity,the inoculation of strain SQR9 increased the expression of WRKY29 and ERF1B encoding for transcription factors involved in immune signaling pathway,which could induce the host systemic resistance and enhance the disease resistance;moreover,genes encodes for stress resistance factor C_(4)H and ADH1,were significantly activated by inoculation.[Conclusions]PGPR strain SQR9 promotes cucumber plants growth and enhances disease resistance through activation of genes involved in metabolism and immune pathway.