Abstract
Pears (Pyrus sp.) are widely cultivated in China, and their yield accounts for more than 60% of global pear production. The fungal pathogen Valsa pyri is a major causal agent of pear canker disease, which results in enormous losses of pear production in northern China. In this study, we characterized a Zn2Cys6 transcription factor that contains one GAL4 domain and a fungal-trans domain, which are present in VpxlnR. The vpxlnR gene expression was upregulated in the invasion stage of V. pyri. To investigate its functions, we constructed gene deletion mutants and complementary strains. We observed that the growth of the vpxlnR mutants was reduced on potato dextrose agar (PDA), Czapek plus glucose or sucrose compared with that of the wild-type strain. Additionally, vpxlnR mutants exhibited loss of function in fruiting body formation. Moreover, vpxlnR mutants were more susceptible to hydrogen peroxide (H2O2) and salicylic acid (SA) and were reduced in their virulence at the early infection stage. According to a previous study, VpxlnR-interacting motifs containing NRHKGNCCGM were searched in the V. pyri genome, and we obtained 354 target genes, of which 148 genes had Clusters of Orthologous Groups (COG) terms. PHI-BLAST was used to identify virulence-related genes, and we found 28 hits. Furthermore, eight genes from the 28 PHI-BLAST hits were further assessed by yeast one-hybrid (Y1H) assays, and five target genes, salicylate hydroxylase (VP1G_09520), serine/threonine-protein kinase (VP1G_03128), alpha-xylosidase (VP1G_06369), G-protein beta subunit (VP1G_02856), and acid phosphatase (VP1G_03782), could interact with VpxlnR in vivo. Their transcript levels were reduced in one or two vpxlnR mutants. Taken together, these findings imply that VpxlnR is a key regulator of growth, development, stress, and virulence through controlling genes involved in signaling pathways and extracellular enzyme activities in V. pyri. The motifs interacting with VpxlnR also provide new insights into the molecular mechanism of xlnR proteins.
Highlights
Pear is the third most highly produced fruit in China
We found that many genes in V. pyri were annotated as xlnR homologues through RNA-Seq analysis (He et al, 2018), and its unigene (c14467) was reidentified through de novo assembly using transcriptome data
We found that the gene contains four introns; the genome assembly was missing a 12-bp sequence, which might cause the prediction using genomics and transcriptomics to vary (Supplementary Figure S1)
Summary
Valsa canker disease is one of the most destructive diseases in most orchards of northern China. The disease is caused by the fungal pathogen Valsa pyri, which belongs to Ascomycetes in the Valsaceae family (Sordariomycetes, Diaporthales; Yin et al, 2015). This fungus can infect pear trees from natural wound sites on the bark and form cankers, which result in great yield loss or tree death [3, 4]. Valsa pyri is a necrotrophic pathogen that can penetrate the phloem and xylem (Yin et al, 2015). It was shown that transcription factors (TFs), cell wall-degrading enzymes, and genes involved in nitrogen metabolism might be important for the virulence and growth of V. pyri strains (He et al, 2018; Xu et al, 2018). Very few studies have been conducted to investigate the roles of TFs in the pathogenesis of V. pyri
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
