Transcriptome analysis of a powdery mildew pathogen (Podosphaera pannosa) infecting Eucalyptus urophylla: De novo assembly, expression profiling and secretome prediction

Abstract

AbstractPodosphaera pannosa is the causal agent of powdery mildew on eucalypt in Brazil. This powdery mildew disease is important in nurseries causing leaf and shoot distortion, shoot discoloration and reduction in growth, which decreases mini‐cutting production. Improved RNA sequencing (RNA‐Seq) technologies have allowed increased information about the transcriptome of several pathogens and hosts, enabling a better understanding of their interaction at the gene level. For this study, we analysed the transcriptome of P. pannosa during leaf infection of Eucalyptus urophylla leaves using RNA‐Seq and de novo transcriptome assembly. The transcriptome was Illumina sequenced and assembled de novo, generating over 178 million RNA‐Seq reads assembled onto 200,473 contigs. After filtering steps, the resulting 12,106 (6%) transcripts were identified as the P. pannosa transcriptome data set. The 10 most abundant transcripts included genes encoding enzymes likely involved in fungal establishment and growth, such as dihydrofolate reductase, putative methyltransferases, acyl‐desaturase, glycoside hydrolase and dehydrogenases. In addition, genes putatively encoding an aquaporin and an orthologue to the effector protein, GoEC2 of Golovinomyces orontii were identified. The predicted secretome consisted of 1,899 translated transcripts, of which 310 exhibited homology to proteins described in the PHI database, 144 of these showing homology to fungal PHI accessions that affected pathogenicity or that are described as effectors. In addition, 81 transcripts encoded secreted proteins homologous to effectors described in the Erysiphales. These results provide a basis for continued studies to better understand the P. pannosa‐eucalypt (Eucalyptus spp.) pathosystem and could parallel studies of the eucalypt transcriptome to help determine host resistance mechanisms.