Divergent gene expression levels between diploid and autotetraploid Tolmiea (Saxifragaceae) relative to the total transcriptome, the cell, and biomass
SummaryStudies of gene expression and polyploidy are typically restricted to characterizing differences in transcript concentration. Integrating multiple methods of transcript analysis, we document a difference in transcriptome size, and make multiple comparisons of transcript abundance in diploid and autotetraploid Tolmiea.We use RNA spike-in standards to identify and correct for differences in transcriptome size, and compare levels of gene expression across multiple scales: per transcriptome, per cell, and per biomass.In total, ~17% of all loci were identified as differentially expressed (DEGs) between the diploid and autopolyploid species. A shift in total transcriptome size resulted in only ~58% of the total DEGs being identified as differentially expressed following a per transcriptome normalization. When transcript abundance was normalized per cell, ~82% of the total DEGs were recovered. The discrepancy between per-transcriptome and per-cell recovery of DEGs occurs because per-transcriptome normalizations are concentration-based and therefore blind to differences in transcriptome size.While each normalization enables valid comparisons at biologically relevant scales, a holistic comparison of multiple normalizations provides additional explanatory power not available from any single approach. Notably, autotetraploid loci tend to conserve diploid-like transcript abundance per biomass through increased gene expression per cell, and these loci are enriched for photosynthesis-related functions.