Comparative transcriptome analysis and marker development of two closely related Primrose species (Primula poissonii and Primula wilsonii)

Abstract

BackgroundPrimula species are important early spring garden plants with a centre of diversity and speciation in the East Himalaya-Hengduan Mountains in Western China. Studies on population genetics, speciation and phylogeny of Primula have been impeded by a lack of genomic resources. In the present study, we sequenced the transcriptomes of two closely related primrose species, Primula poissonii and Primula wilsonii, using short reads on the Illumina Genome Analyzer platform.ResultsWe obtained 55,284 and 55,011 contigs with N50 values of 938 and 1,085 for P. poissonii and P. wilsonii, respectively, and 6,654 pairs of putative orthologs were identified between the two species. Estimations of non-synonymous/synonymous substitution rate ratios for these orthologs indicated that 877 of the pairs may be under positive selection (Ka/Ks > 0.5), and functional enrichment analysis revealed that significant proportions of the orthologs were in the categories DNA repair, stress resistance, which may provide some hints as to how the two closely related Primula species adapted differentially to extreme environments, such as habitats characterized by aridity, high altitude and high levels of ionizing radiation. It was possible for the first time to estimate the divergence time between the radiated species pair, P. poissonii and P. wilsonii; this was found to be approximately 0.90 ± 0.57 Mya, which falls between the Donau and Gunz glaciation in the Middle Pleistocene. Primers based on 54 pairs of orthologous SSR-containing sequences between the two Primula species were designed and verified. About half of these pairs successfully amplified for both species. Of the 959 single copy nuclear genes shared by four model plants (known as APVO genes), 111 single copy nuclear genes were verified as being present in both Primula species and exon-anchored and intron-spanned primers were designed for use.ConclusionWe characterized the transcriptomes for the two Primula species, and produced an unprecedented amount of genomic resources for these important garden plants. Evolutionary analysis of these two Primula species not only revealed a more precise divergence time, but also provided some novel insights into how differential adaptations occurred in extreme habitats. Furthermore, we developed two sets of genetic markers, single copy nuclear genes and nuclear microsatellites (EST-SSR). Both these sets of markers will facilitate studies on the genetic improvement, population genetics and phylogenetics of this rapidly adapting taxon.

Transcriptomic resources for an endemic Neotropical plant lineage (Gesneriaceae)

“…This number is comparable with other surveys between closely related species (Zhang et al, 2013). These orthologous groups provide the information for future molecular evaluations and gene-specific analyses.…”

De novo Sequencing and Comparative Transcriptomics of Floral Development of the Distylous Species Lithospermum multiflorum

“…For example, Fagopyrum, Primula , and each of two species of Eichhornia Kunth express ca. 25,400, 55,000, and 20,000—24,000 genes, respectively (Logacheva et al, 2011; Ness et al, 2011; Zhang et al, 2013). Additionally, the transcriptome of L. multiflorum is greater than that of the only other species of Boraginaceae, Echium wildpretii H. Pearson ex.…”

Transcriptome analysis of two radiated Cycas species and the subsequent species delimitation of the Cycas taiwaniana complex

“…The peak K S between C. hainanensis and C. changjiangensis was 0.0062, suggesting that they are very closely related. By comparison, previous research found that the mean K S values between congeneric species in several model plants were 0.03–0.10 (Zhang et al., ). We estimated that C. changjiangensis and C. hainanensis diverged approximately 4.6 mya, in the Middle Pliocene.…”

“…The ratio of non‐synonymous to synonymous substitution rates is considered a good indicator of the natural selection pressure at the sequence level (Zhang et al., ). In this study, six of the 10,195 pairs of orthologs between C. hainanensis and C. changjiangensis were found to be under strong positive selection.…”