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Cell-Type and Tissue Specific Transcriptomes of the White Spruce (Picea Glauca) Bark Unmask Fine-Scale Spatial Patterns of Constitutive and Induced Conifer Defense

By September 13, 2017No Comments

Plant defenses often involve specialized cells and tissues. In conifers, specialized cells of the bark are important for defense against insects and pathogens. Using laser microdissection, we characterized the transcriptomes of cortical resin duct cells, phenolic cells, and phloem of white spruce (Picea glauca) bark under constitutive and methyl jasmonate (MeJa)-induced conditions, and we compared these transcriptomes with the transcriptome of the bark tissue-complex. Overall, ~3,700 bark transcripts were differentially expressed in response to MeJa. Approximately 25% of transcripts were expressed in only one cell-type, revealing cell specialization at the transcriptome level. MeJa caused cell-type specific transcriptome responses and changed the overall patterns of cell-type specific transcript accumulation. Comparison of transcriptomes of the conifer bark tissue-complex and specialized cells resolved a masking effect inherent to transcriptome analysis of complex tissues, and showed the actual cell-type specific transcriptome signatures. Characterization of cell-type specific transcriptomes is critical to reveal the dynamic patterns of spatial and temporal display of constitutive and induced defense systems in a complex plant tissue or organ. This was demonstrated with the improved resolution of spatially restricted expression of sets of genes of secondary metabolism in the specialized cell-types.