Abstract
Wheat yield is greatly reduced because of the occurrence of leaf spot diseases. Bipolaris sorokiniana is the main pathogenic fungus in leaf spot disease. In this study, B. sorokiniana from wheat leaf (W-B. sorokiniana) showed much stronger pathogenicity toward wheat than endophytic B. sorokiniana from Pogostemon cablin (P-B. sorokiniana). The transcriptomes and metabolomics of the two B. sorokiniana strains and transcriptomes of B. sorokiniana-infected wheat leaves were comparatively analyzed. In addition, the expression levels of unigenes related to pathogenicity, toxicity, and cell wall degradation were predicted and validated by quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis. Results indicated that pathogenicity-related genes, especially the gene encoding loss-of-pathogenicity B (LopB) protein, cell wall-degrading enzymes (particularly glycosyl hydrolase-related genes), and killer and Ptr necrosis toxin-producing related unigenes in the W-B. sorokiniana played important roles in the pathogenicity of W-B. sorokiniana toward wheat. The down-regulation of cell wall protein, photosystem peptide, and rubisco protein suggested impairment of the phytosynthetic system and cell wall of B. sorokiniana-infected wheat. The up-regulation of hydrolase inhibitor, NAC (including NAM, ATAF1 and CUC2) transcriptional factor, and peroxidase in infected wheat tissues suggests their important roles in the defensive response of wheat to W-B. sorokiniana. This is the first report providing a comparison of the transcriptome and metabolome between the pathogenic and endophytic B. sorokiniana strains, thus providing a molecular clue for the pathogenic mechanism of W-B. sorokiniana toward wheat and wheat’s defensive response mechanism to W-B. sorokiniana. Our study could offer molecular clues for controlling the hazard of leaf spot and root rot diseases in wheat, thus improving wheat yield in the future.
Highlights
Wheat is an important global economic crop, and is the most widely cultivated plant worldwide
Most enzymes involved in the aflatoxin biosynthesis in P-B. sorokiniana were down-regulated compared with W-B. sorokiniana according to the Kyoto Encyclopedia of Genes and Genomes (KEGG) annotation of the two B. sorokiniana strains (Figure S5), which was in accordance with the quantitative reverse transcription polymerase chain reaction (qRT-polymerase chain reaction (PCR)) results (Figure 7).The fmk1 gene encoding a mitogen-activated protein kinase (MAPK) of Fusarium oxysporum was reported to be essential for root penetration and pathogenesis toward tomatoes [37]
This study is the first report on a comparative transcriptome combined with metabolome analysis between the two B. sorokiniana strains derived from P. cablin and wheat leaves, respectively, and the comparative transcriptomes of the two B. sorokiniana strain-infected wheat leaves were firstly investigated
Summary
Wheat is an important global economic crop, and is the most widely cultivated plant worldwide. The expression levels of unigenes related to the spore formation, the pathogenic protein, the degradation of cell wall, and the toxin-production in the two B. sorokiniana strains were predicted and validated by quantitative reverse transcription polymerase chain reaction (qRT-PCR). The endophytic strain P-B. sorokiniana was cultivated on potato dextrose agar (PDA) medium at 28 ◦C for three days (samples A3-1 and A3-2) and seven days (samples A7-1 and A7-2), respectively, and the pathogenic W-B. sorokiniana isolated from infected leaf tissues was cultivated on PDA medium at 28 ◦C for seven days (samples B7-1 and B7-2) These samples were collected and transcriptome sequenced. More unigenes related to pathogenicity and spore formation showed higher expression levels in the A7 group than in the A3 group. TMhoerreeosvueltrs, inaldlictahteed1t6hautntihgeepnaetshoegnecnoidciintyg-redliasteeadsep-rroetseisintaanncde spproorteeifnormshaotiwoned-reslaigtendifipcraontteliyn hhaigvheear celxopserersesliaotniolnesvheilps iwnitthhethWeBpagtrhoougpenaisccitoymopf aBr.esdortookitnhieanCaK. and PB groups (Figure 5C)
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