Search

Background Perennial ryegrass (Lolium perenne L.) is one of the most important forage and turf grass species of temperate regions worldwide. Its mitochondrial genome is inherited maternally and contains genes that can influence traits of agricultural importance. Moreover, the DNA sequence of mitochondrial genomes has been established and compared for a large number of species in order to characterize evolutionary relationships. Therefore, it is crucial to understand the organization of the mitochondrial genome and how it varies between and within species. Here, we report the first de novo assembly and annotation of the complete mitochondrial genome from perennial ryegrass. Results Intact mitochondria from perennial ryegrass leaves were isolated and used for mtDNA extraction. The mitochondrial genome was sequenced to a 167-fold coverage using the Roche 454 GS-FLX Titanium platform, and assembled into a circular master molecule of 678,580 bp. A total of 34 proteins, 14 tRNAs and 3 rRNAs are encoded by the mitochondrial genome, giving a total gene space of 48,723 bp (7.2%). Moreover, we identified 149 open reading frames larger than 300 bp and covering 67,410 bp (9.93%), 250 SSRs, 29 tandem repeats, 5 pairs of large repeats, and 96 pairs of short inverted repeats. The genes encoding subunits of the respiratory complexes – nad1 to nad9, cob, cox1 to cox3 and atp1 to atp9 – all showed high expression levels both in absolute numbers and after normalization. Conclusions The circular master molecule of the mitochondrial genome from perennial ryegrass presented here constitutes an important tool for future attempts to compare mitochondrial genomes within and between grass species. Our results also demonstrate that mitochondria of perennial ryegrass contain genes crucial for energy production that are well conserved in the mitochondrial genome of monocotyledonous species. The expression analysis gave us first insights into the transcriptome of these mitochondrial genes in perennial ryegrass.

The development of next-generation sequencing technologies has made sequencing an affordable approach for detection of genetic variations associated with various traits. However, the cost of whole genome re-sequencing still remains too high to be feasible for many plant species with large and complex genomes. Recent developments in strategies for target-enrichment, transcriptome re-sequencing, and partial genome re-sequencing allows for enrichment for regions of interest at a scale that is matched to the throughput of next-generation sequencing platforms, and has emerged as a promising alternative to whole genome re-sequencing to identify causative genetic variations in plants. One challenge, however, will be efficient bioinformatics strategies for data handling and analysis from the increasing amount of sequence information. The development of next-generation sequencing technologies has made sequencing an affordable approach for detection of genetic variations associated with various traits. However, the cost of whole genome re-sequencing still remains too high to be feasible for many plant species with large and complex genomes. Recent developments in strategies for target-enrichment, transcriptome re-sequencing, and partial genome re-sequencing allows for enrichment for regions of interest at a scale that is matched to the throughput of next-generation sequencing platforms, and has emerged as a promising alternative to whole genome re-sequencing to identify causative genetic variations in plants. One challenge, however, will be efficient bioinformatics strategies for data handling and analysis from the increasing amount of sequence information.