Suitability of Illumina deep mRNA sequencing for reliable gene expression profiling in a non-model conifer species ( Pse

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ORIGINAL PAPER

Suitability of Illumina deep mRNA sequencing for reliable gene expression profiling in a non-model conifer species (Pseudotsuga menziesii ) Moritz Hess & Henning Wildhagen & Ingo Ensminger

Received: 20 February 2013 / Revised: 11 July 2013 / Accepted: 5 August 2013 / Published online: 21 September 2013 # Springer-Verlag Berlin Heidelberg 2013

Abstract Pseudotsuga menziesii (Douglas-fir) is an ideal model system to study the effect of local adaptation and intraspecific variation in transcriptome responses to the environment. Nonetheless, the lack of genomic resources and standardized microarray platforms for gene expression profiling has been a limitation to test the hypothesis on transcriptome organization and variation. Only recently, deep mRNA sequencing has become a promising alternative to overcome the present limitations. However, information on the transcript abundance distribution is needed for unbiased gene expression profiling from mRNA sequencing data. Since this information

Communicated by J. Wegrzyn Electronic supplementary material The online version of this article (doi:10.1007/s11295-013-0656-2) contains supplementary material, which is available to authorized users. M. Hess : H. Wildhagen : I. Ensminger Forest Research Institute of Baden-Württemberg (FVA), Wonnhaldestrasse 4, 79100 Freiburg, Germany M. Hess e-mail: [email protected] H. Wildhagen e-mail: [email protected] M. Hess Institute of Biology III, Faculty of Biology, Albert Ludwigs University Freiburg, Schänzlestrasse 1, 79104 Freiburg, Germany I. Ensminger (*) Department of Biology, University of Toronto Mississauga, 3359 Mississauga Road North, Mississauga, Ontario, Canada L5L 1C6 e-mail: [email protected] Present Address: H. Wildhagen Department of Forest Botany and Tree Physiology, Büsgen-Institute, Georg-August-University Göttingen, Büsgenweg 2, 37077 Göttingen, Germany

is not available for adult conifer needle tissue, we inferred the transcript abundance distribution and tested the effect of sequencing depth on the reliable detection and quantification of transcripts from the needle tissue of 50-year-old Douglas-fir trees. We obtained a similar distribution of GO-slim categories in our mRNA-sequencing libraries and in previously published putative unique transcripts (PUTs) for Douglas-fir, that were used as alignment reference. However, the GO-slim distribution in the Douglas-fir libraries and the Douglas-fir PUTs differed from the GO-slim distributions reported from mRNA deep sequencing libraries obtained from Arabidopsis thaliana leaf tissue. Apparently, several highly abundant PUTs associated with proteins involved in photosynthesis were limiting the benefits of increased sequencing depth. Simulations and empirical data indicated that a 3-fold increase from 5 to 15 million aligned reads results in about twice the number of PUTs that surpass the 100 aligned reads threshold that was used for robust transcript quantification.

Keywords Illumina . Deep mRNA sequencing . Conifer . Sequenci