A comparative transcriptomic study of an allotetraploid and its diploid progenitors illustrates the unique advantages and challenges of RNA-seq in plant species.
OBJECTIVE
RNA-seq analysis of plant transcriptomes poses unique challenges due to the highly duplicated nature of plant genomes. We address these challenges in the context of recently formed polyploid species and detail an RNA-seq experiment comparing the leaf transcriptome profile of an allopolyploid relative of soybean with the diploid species that contributed its homoeologous genomes.


METHODS
RNA-seq reads were obtained from the three species and were aligned against the genome sequence of Glycine max. Transcript levels were estimated for each gene, relative contributions of polyploidy-duplicated loci (homoeologues) in the tetraploid were identified, and comparisons of transcript profiles and individual genes were used to analyze the regulation of transcript levels.


RESULTS
We present a novel metric developed to address issues arising from high degrees of gene space duplication and a method for dissecting a gene's measured transcript level in a polyploid species into the relative contribution of its homoeologues. We identify the gene family likely contributing to differences in photosynthetic rate between the allotetraploid and its progenitors and show that the tetraploid appears to be using the "redundant" gene copies in novel ways.


CONCLUSIONS
Given the prevalence of polyploidy events in plants, we believe many of the approaches developed here to be applicable, and often necessary, in most plant RNA-seq experiments. The deep sampling provided by RNA-seq allows us to dissect the genetic underpinnings of specific phenotypes as well as examine complex interactions within polyploid genomes.
Department of Plant Biology, Cornell University, Ithaca, New York 14853, USA. dci1@cornell.edu
Daniel C
DC
Ilut
Jeremy E
JE
Coate
Amelia K
AK
Luciano
Thomas G
TG
Owens
Gregory D
GD
May
Andrew
A
Farmer
Jeff J
JJ
Doyle
D001483:Base Sequence; D002734:Chlorophyll / Q000032:analysis; D003198:Computer Simulation; D004171:Diploidy; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D008957:Models, Genetic; D010641:Phenotype; D010788:Photosynthesis / Q000235:genetics; D018515:Plant Leaves / Q000235:genetics; D018749:RNA, Plant / Q000235:genetics; D016415:Sequence Alignment; D017423:Sequence Analysis, RNA / Q000379:methods*; D012689:Sequence Homology, Nucleic Acid; D013025:Glycine max / Q000235:genetics; D057891:Tetraploidy; D059467:Transcriptome
D018749:RNA, Plant; D002734:Chlorophyll