Profiling methyl jasmonate-responsive transcriptome for understanding induced systemic resistance in whitebark pine (Pinus albicaulis)
RNA-seq analysis on whitebark pine needles demonstrated that methyl jasmonate (MeJA)-triggered transcriptome re-programming substantially overlapped with defense responses against insects and fungal pathogens in Pinus species, increasing current knowledge regarding induced systemic resistance (ISR) to pathogens and pests in whitebark pine.
Many whitebark pine populations are in steep decline due to high susceptibility to mountain pine beetle and the non-native white pine blister rust (WPBR). Resistance, including induced systemic resistance (ISR), is not well characterized in whitebark pine, narrowing the current options for increasing the success of restoration and breeding programs. Exogenous jasmonates are known to trigger ISR by activating the plant’s immune system through regulation of gene expression to produce chemical defense compounds. This study reports profiles of whitebark pine needle transcriptomes, following methyl jasmonate (MeJA) treatment using RNA-seq. A MeJA-responsive transcriptome was de novo assembled and transcriptome profiling identified a set of differentially expressed genes (DEGs), revealing 1422 up- and 999 down-regulated transcripts with at least twofold change (FDR corrected p < 0.05) in needle tissues in response to MeJA application. GO analysis revealed that these DEGs have putative functions in plant defense signalling, transcription regulation, biosyntheses of secondary metabolites, and other biological processes. Lineage-specific expression of defense-related genes was characterized through comparison with MeJA signalling in model plants. In particular, MeJA-triggered transcriptome re-programming substantially overlapped with defense responses against WPBR and insects in related Pinus species, suggesting that MeJA may be used to improve whitebark pine resistance to pathogens/pests. Our study provides new insights into molecular mechanisms and metabolic pathways involved in whitebark pine ISR. DEGs identified in this study can be used as candidates to facilitate identification of genomic variation contributing to host resistance and aid in breeding selection of elite genotypes with better adaptive fitness to environmental stressors in this endangered tree species.
KeywordsInduced systemic resistance Jasmonate-signaling RNA-seq Transcriptome profiling Whitebark pine
Authors are grateful to Gary Zhang and Aimin Guan at CFS for computer programming and bioinformatics analyses, and to Andrew Dyk at CFS for photographing. This work was financially supported in part by the CFS-GRDI fund and CFS-PFC DG’s fund. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
J-JL, AWS and RAS conceived the project. J-J L and HW designed the experiments. MM provided plant materials. HW, XRL, AZ, and GR performed the experiments. J-JL, HW, XRL, and HC performed the bioinformatics of the transcriptome and the statistical analyses of the experimental data. J-JL interpreted the data and wrote the manuscript. J-JL, HW, MM, AWS, RAS, and AZ edited the manuscript.
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