Molecular mechanism and gene mining of passion fruit（Passiflora edulis） in response to infection of Phytophthora nicotianae

【Objective】The objective of this study was to analyze the expression patterns of passion fruit in response to the infection of Phytophthora nicotianae at the transcriptional level and identify the resistance-related genes and their mechanism， which provided a foundation for the screening of disease-resistance traits and breeding of disease-resistance varieties of passion fruit by molecular means. 【Method】The main cultivar of passion fruit Qinguo No. 9 was as the test material， and the tissue phenotype observation and physiological index determination of Qinguo No. 9 infected by P. nicotianae at 12， 24， 48， 72 and 96 hpi were carried out. The transcriptome of Qinguo No. 9 in response to P. nicotianae infection was constructed by transcriptome sequencing RNA-Seq. DESeq software was used to analyze the differences in gene expression， and differentially expressed genes（DEGs） were screened with the criteria of significant difference P<0.005， false discovery rate （FDR）≤0.001 and |log₂ Ratio|≥1. GO functional annotation analysis and KEGG signaling pathway enrichment analysis of DEGs were carried out by BLAST2GO and KOBAS2 to clarify the main pathways and metabolism pathways of Qinguo No. 9 in response to P. nicotianae infection. The DEGs of metabolism pathways related to plant disease resistance were screened out and the gene expression patterns were analyzed with MeV software to construct the heat maps， and the dynamic change trend of DEGs in the process of P. nicotianae infecting Qinguo 9 was analyzed. The difference in gene expression was verified by real-time fluorescence quantitative PCR to be consistent with the transcriptome data. 【Result】There were no obvious symptoms in the early stage of infection in the leaves of Qinguo No. 9 by P. nicotianae， but the leaves appeared chlorotic at 48 hpi. The lesions became darker and expanded to obvious brown wilt spots accompany with infection time. The superoxide dismutase （SOD） activity in all treatments groups of Qinguo No. 9 were significantly higher than that of in control groups from 12 hpi（P<0.05）， and SOD activity reached the peak at 24 hpi. This indicated that P. nicotianae had begun to invade the leaves of Qinguo No. 9 from the wound at the early stage of infection. A total of 7163 DEGs were screened by transcriptome analysis. KEGG signaling pathway enrichment analysis showed that DEGs were mainly enriched in pathways of plant hormone signaling transduction， plant-pathogen interaction， phenylpropanoid biosynthesis， MAPK signaling pathway and flavonoid biosynthesis， which were related to plant disease resistance， indicating that these pathways may be the main metabolism pathways of passion fruit in response to P. nicotianae infection at transcriptional level. Genes of PR1， CERK1， RPM1， CDPK， CML in the plant-pathogen interaction pathway， genes of JAR1， JAZ2， ERF1， EBF1 and ERS in the jasmonic acid （JA）/ethylene （ET） signaling pathway， and secondary metabolism-related genes of CAD6， 4CL， POD， CHS， and LDOX were significantly up-regulated in Qinguo No. 9 infected with P. nicotianae. This suggested that these genes might be involved in the resistance of passion fruit to P. nicotianae. Real-time fluorescence quantitative PCR results verified the reliability of RNA-Seq data. 【Conclusion 】Plant hormone signaling transduction， plant-pathogen interaction， phenylpropanoid biosynthesis， MAPK signaling pathway and flavonoid biosynthesis are the main signaling and metabolism pathways of passion fruit against P. nicotianae infection. The key genes in different metabolism pathways are involved in resistance of passion fruit to P. nicotianae in complex ways.