Dataset Information

Functional innovations of three chronological mesohexaploid Brassica rapa genomes.

ABSTRACT:

Background

The Brassicaceae family is an exemplary model for studying plant polyploidy. The Brassicaceae knowledge-base includes the well-annotated Arabidopsis thaliana reference sequence; well-established evidence for three rounds of whole genome duplication (WGD); and the conservation of genomic structure, with 24 conserved genomic blocks (GBs). The recently released Brassica rapa draft genome provides an ideal opportunity to update our knowledge of the conserved genomic structures in Brassica, and to study evolutionary innovations of the mesohexaploid plant, B. rapa.

Results

Three chronological B. rapa genomes (recent, young, and old) were reconstructed with sequence divergences, revealing a trace of recursive WGD events. A total of 636 fast evolving genes were unevenly distributed throughout the recent and young genomes. The representative Gene Ontology (GO) terms for these genes were 'stress response' and 'development' both through a change in protein modification or signaling, rather than by enhancing signal recognition. In retention patterns analysis, 98% of B. rapa genes were retained as collinear gene pairs; 77% of those were singly-retained in recent or young genomes resulting from death of the ancestral copies, while others were multi-retained as long retention genes. GO enrichments indicated that single retention genes mainly function in the interpretation of genetic information, whereas, multi-retention genes were biased toward signal response, especially regarding development and defense. In the recent genome, 13,302, 5,790, and 20 gene pairs were multi-retained following Brassica whole genome triplication (WGT) events with 2, 3, and 4 homoeologous copies, respectively. Enriched GO-slim terms from B. rapa homomoelogues imply that a major effect of the B. rapa WGT may have been to acquire environmental adaptability or to change the course of development. These homoeologues seem to more frequently undergo subfunctionalization with spatial expression patterns compared with other possible events including nonfunctionalization and neofunctionalization.

Conclusion

We refined Brassicaceae GB information using the latest genomic resources, and distinguished three chronologically ordered B. rapa genomes. B. rapa genes were categorized into fast evolving, single- and multi-retention genes, and long retention genes by their substitution rates and retention patterns. Representative functions of the categorized genes were elucidated, providing better understanding of B. rapa evolution and the Brassica genus.

SUBMITTER: Kim J

PROVIDER: S-EPMC4117954 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Two Chinese cabbage (Brassica rapa ssp. pekinensis) inbred lines, Chiifu (smaple A) and Kenshin (Smaple B), were grown for approximately 4 weeks in a growth chamber at 22degreesC under a 16 h light/8 h dark photoperiod with a photon flux density of 140 umol m-2 s-1. For microarray analysis, plants were exposed to a temperature of -4degreesC for 4 h, and shoots were sampled. Total RNA was isolated from the samples using an Easy-BLUETM Total RNA Extraction Kit (Invitrogen, NY, U.S.A.) and was then purified using an RNeasy MinEluteTM Cleanup Kit (Qiagen, Germany). Mircroarray experiments were carried out using Brassica 24K Oligo Microarray. RNA were prepared from each plant sample and 10 ug of total RNA were used for cDNA synthesis by using Superscript Double-Stranded cDNA Synthesis Kit (Invitrogen, NY, U.S.A.). Following cDNA synthesis, remaining RNA was removed by the addition of RNaseA and the cDNA was precipitated following phenol/chloroform extraction. The cDNA pellet was rehydrated and used for Cy3-labelling. For the synthesis of Cy3-labeled target DNA fragments, 1 ug of double strand cDNA was mixed with 40 ul (1 OD) of Cy3-9 mer primers (Sigma-Aldrich) and the total volume was adjusted to 80 ul with deionized water. After heating at 98degreesC for 10 min, 10 uL of dNTP mix (10 mM each) and 2 ul of Klenow fragment (NEB; 50 units/ul) were added and the reaction was incubated at 37degreesC for 2 h. Finally, the reaction was stopped by the addition of 10 ul of 0.5 M EDTA. Labeled DNA fragments were precipitated with isopropanol and rehydrated with water. The concentration of each sample was determined using spectrophotometer. For hybridization, 13 ug of the labeled DNA fragment was mixed with hybridization buffer (NimbleGen) and then hybridized with the microarray using a MAUI hybridization chamber (Biomicro) at 42degreesC for 16 h. Following hybridization, the microarray was washed with wash solution I, II, and III (NimbleGen), and then dried in a dark desiccator. The microarray slide was scanned using GenePix scanner 4000B (Axon) and the spot intensities were analyzed using a NimbleScan (NimbleGen). The normal distribution of Cy3 intensities was tested by qqline. The data was normalized and processed with cubic spline normalization using quantiles to adjust signal variations between chips and with Rubust Multi-Chip Analysis (RMA) using a median polish algorithm implemented in NimbleScan software (NimbleGen). Two biological replicates were carried out.