Transcriptome Profiling in Hybrid Poplar Following Interactions with Melampsora Rust Fungi

Abstract

In natural conditions, plants are subjected to a combination of biotic stresses and often have to cope with simultaneous pathogen infections. In this report, we aim to understand the global transcriptional response of hybrid poplar NM6 (Populus nigra x P. maximowiczii) to infection by two biotrophic Melampsora fungi, Melampsora larici-populina and M. medusae f. sp. deltoidae. These pathogens triggered different responses after inoculation of poplar leaves. Transcript profiling using the GeneChip Poplar Genome Array revealed a total of 416 differentially expressed transcripts whose expression level was > or = twofold relative to controls. Interestingly, approximately half of the differentially expressed genes in infected leaves showed altered expression following interaction with either of the Melampsora spp. We also infected poplar leaves simultaneously with both Melampsora spp. to investigate potential interaction between the responses to the individual pathogens during a mixed infection. For this mixed inoculation, the number of differentially expressed transcripts increased to 648 and our analysis showed that infection with both fungi also induced a common set of genes. The genes induced after Melampsora spp. infection were mainly related to primary and secondary metabolic processes, cell-wall reinforcement and lignification, defense and stress-related mechanisms, and signal perception and transduction.

Leaf endophytes and Populus genotype affect severity of damage from the necrotrophic leaf pathogen, Drepanopeziza populi

“…Despite this, the trends we observed in gene expression are informative. Supporting previous work on quantitative resistance in Populus (Miranda et al 2007, Azaiez et al 2009), several defense-related genes were strongly up regulated (.5 fold) following pathogen inoculation (e.g., Ptgluc, PtATOSM34, PtGSTU25, PtWRKY51, PtCAD9) (Table 1). In particular, the expression of PtATOSM34, a gene coding for a defense protein, was more than 38 times greater in plants inoculated with Drepanopeziza than in control plants (Table 1).…”

“…Two genes of particular interest-PtATOSM34 and PtGlyHy17-code for defense-related proteins. A previous study found all fifteen genes were up-regulated in response to inoculation with the rust pathogen Melampsora (Azaiez et al 2009). …”

Stress-Responsive Mitogen-Activated Protein Kinases Interact with the EAR Motif of a Poplar Zinc Finger Protein and Mediate Its Degradation through the 26S Proteasome

“…2B). Mmd rust is known to elicit a strong defense response in this hybrid poplar (Azaiez et al, 2009;Boyle et al, 2010), as suggested here by the increase in PtiPR1 transcript in the infected leaves (Fig. 2B).…”

“…Infection of NM6 poplar with Mmd rust results in host-specific partial resistance that still allows a certain extent of fungal growth. NM6 hybrids are thus considered susceptible, and the defense response (quantitative resistance) associated with this host-microbe interaction was described elsewhere (Azaiez et al, 2009;Boyle et al, 2010). Among the peptides selected for their potential interaction with PtiMPK3-1, we identified a truncated cDNA coding for the last 104 amino acids of a putative TF.…”

“…Poplar (Populus spp.) trees, for instance, respond to herbivory or pathogen infection by reconfiguring their transcriptome, including the upregulation of numerous defense-related genes (Ralph et al, 2006;Rinaldi et al, 2007;Major and Constabel, 2008;Azaiez et al, 2009;Duplessis et al, 2009;Philippe et al, 2010). Transcription factors (TFs) play a pivotal role in reprogramming the plant transcriptome, and several candidates have been identified as regulators of the plant defense response, including subgroups of zinc fingers, AP2-ERFs, bZIPs, WRKYs, and bHLHs (Eulgem, 2005), although few have been characterized for poplar.…”