Transcriptome analysis reveals underlying immune response mechanism of fungal (Penicillium oxalicum) disease in Gastrodia elata Bl. f. glauca S. chow (Orchidaceae)

Abstract

Background: Gastrodia elata Bl. f. glauca S. Chow is a medicinal plant. G. elata f. glauca is unavoidably infected by pathogens in their growth process. In previous work, we have successfully isolated and identified Penicillium oxalicum from fungal diseased tubers of G. elata f. glauca. As a widespread epidemic, this fungal disease seriously affected the yield and quality of G. elata f. glauca. We speculate that the healthy G. elata F. glauca might carry resistance genes, which can resist against fungal disease. In this study, healthy and fungal diseased mature tubers of G. elata f. glauca from Changbai Mountain area were used as experimental materials to help us find potential resistance genes against the fungal disease.

Results: A total of 7540 differentially expressed Unigenes (DEGs) were identified (FDR < 0.01, log2FC > 2). The current study screened 10 potential resistance genes. They were attached to transcription factors (TFs) in plant hormone signal transduction pathway and plant pathogen interaction pathway, including WRKY22, GH3, TIFY/JAZ, ERF1, WRKY33, TGA. In addition, four of these genes were closely related to jasmonic acid signaling pathway.

Conclusions: The immune response mechanism of fungal disease in G. elata f. glauca is a complex biological process, involving plant hormones such as ethylene, jasmonic acid, salicylic acid and disease-resistant transcription factors such as WRKY, TGA.

Keywords: Changbai Mountain area; Fungal disease; immune response; Gastrodia elata Bl. f. glauca S. chow; Orchidaceae; Transcription factors; Transcriptome.

Fig. 1

DEGs functional annotation information. a DEGs number annotated into KEGG, GO, KOG, Swiss-Prot, Pfam, eggNOG, nr and total number of annotated DEGs. b Venn diagram of DEGs number annotated into KEGG, GO, Pfam, nr. c Functional classification of DEGs annotated into eggNOG. d Functional classification of DEGs annotated into KOG. Capital letters A ~ Z represent different functional categories

Fig. 2

Unigenes function enrichment analysis. a Top 30 GO enriched function categories with the largest number of annotated Unigenes. b Statistics of KEGG pathway enrichment. Each circle represents a KEGG pathway. c Top 50 KEGG enriched function categories with the largest number of annotated Unigenes

Fig. 3

Differential expression analysis. Each dot represents a gene. Green represents down-regulation; red represents up-regulation; black represents non-differentially expression. a Volcano map of DEGs. X-axis represents the log2(FC) value. The greater the absolute value of log2(FC), the greater the difference of gene expression level between the two groups. Y-axis represents the negative log10(FDR) value. The larger the value, the more significant the difference, as well the more reliable the DEGs. b MA plot of DEGs. MA plot displays the normalized gene distribution. X-axis represents the log2(FPKM) value, and Y-axis represents the log2(FC) value

Fig. 4

Transcription factor prediction. X-axis represents the names of transcription factor family, and Y-axis represents the number of DEGs

Fig. 5

Plant-pathogen interaction map. Positive regulation is highlighted in red; negative regulation is highlighted in green

Fig. 6

Plant hormone signal transduction map. Positive regulation is highlighted in red; negative regulation is highlighted in green; mixed regulation is highlighted in blue

Fig. 7

Brassinosteroid biosynthesis map. Positive regulation is highlighted in red; negative regulation is highlighted in green; mixed regulation is highlighted in blue

Fig. 8

Cluster heatmap of immune response genes of fungal disease. Red indicates positive regulation and green indicates negative regulation. The gene expression levels are indicated by log2FPKM values and displayed in shades of color. The darker the color, the greater the log2FPKM value, and the higher the gene expression level

Fig. 9

Relative expression levels of nine potential immune response genes by qRT-PCR assays. The relative expression levels are displayed with the 2^-ΔΔCt values. All genes but c32310 show significant differential expression between HGe and DGe groups (p < 0.05)

Fig. 10

Phylogenetic tree of TIFY10 in Orchidaceae plants. Branch length represents the credibility of homology. The shorter the branch, the higher the credibility of homology. Different species are displayed with different symbols. ▲(solid triangle): G. elata Bl. f. glauca; △(hollow triangle): Dendrobium catenatum; ○(circle): Phalaenopsis equestris; □(square): Apostasia shenzhenica