Isolation of high molecular weight DNA suitable for BAC library construction from woody perennial soft-fruit species

β-mercaptoethanol assists efficient construction of sperm bacterial artificial chromosome library

Bacterial artificial chromosome (BAC) library plays a critical role in the strategic research in genomics. Sperm is known as a good source for BAC library construction. However, preparation of intact DNA from the highly condensed sperm nuclei is not easy. Here we developed and validated an efficient DNA extraction strategy for BAC library construction from sperm embedded in agarose plugs. The protocol used a combination of lauroylsarcosine, proteinase K and β-mercaptoethanol (a reducing agent of nucleus) In comparison with the normal protocol without reducing agents, β-mercaptoethanol released high-molecular-weight DNA from the protamines which permit DNA to be packed very densely within the spermatozoan nucleus, without damaging DNA. Extracted DNA by this method was readily digested by restriction enzymes and ideal for BAC library construction.

Genome Mapping in Plant Comparative Genomics

Genome mapping produces fingerprints of DNA sequences to construct a physical map of the whole genome. It provides contiguous, long-range information that complements and, in some cases, replaces sequencing data. Recent advances in genome-mapping technology will better allow researchers to detect large (>1kbp) structural variations between plant genomes. Some molecular and informatics complications need to be overcome for this novel technology to achieve its full utility. This technology will be useful for understanding phenotype responses due to DNA rearrangements and will yield insights into genome evolution, particularly in polyploids. In this review, we outline recent advances in genome-mapping technology, including the processes required for data collection and analysis, and applications in plant comparative genomics.

Molecular genetics and genomics of the Rosoideae: state of the art and future perspectives

The Rosoideae is a subfamily of the Rosaceae that contains a number of species of economic importance, including the soft fruit species strawberry (Fragaria ×ananassa), red (Rubus idaeus) and black (Rubus occidentalis) raspberries, blackberries (Rubus spp.) and one of the most economically important cut flower genera, the roses (Rosa spp.). Molecular genetics and genomics resources for the Rosoideae have developed rapidly over the past two decades, beginning with the development and application of a number of molecular marker types including restriction fragment length polymorphisms, amplified fragment length polymorphisms and microsatellites, and culminating in the recent publication of the genome sequence of the woodland strawberry, Fragaria vesca, and the development of high throughput single nucleotide polymorphism (SNP)-genotyping resources for Fragaria, Rosa and Rubus. These tools have been used to identify genes and other functional elements that control traits of economic importance, to study the evolution of plant genome structure within the subfamily, and are beginning to facilitate genomic-assisted breeding through the development and deployment of markers linked to traits such as aspects of fruit quality, disease resistance and the timing of flowering. In this review, we report on the developments that have been made over the last 20 years in the field of molecular genetics and structural genomics within the Rosoideae, comment on how the knowledge gained will improve the efficiency of cultivar development and discuss how these advances will enhance our understanding of the biological processes determining agronomically important traits in all Rosoideae species.

Towards an understanding of the nature of resistance to Phytophthora root rot in red raspberry

A mapping population segregating for root rot resistance was screened under both field and glasshouse conditions over a number of seasons. Few correlations between field and glasshouse scores were significant. Final root rot scores were significantly negatively correlated with measures of root vigour. Two QTL associated with resistance were identified as were overlapping QTL for root vigour assessments. Markers significantly associated with the traits were used to identify BAC clones, which were subsequently sequenced to examine gene content. A number of genes were identified including those associated with stem cell identity, cell proliferation and elongation in the root zone, control of meristematic activity and organisation, cell signalling, stress response, sugar sensing and control of gene expression as well as a range of transcription factors including those known to be associated with defence. For marker-assisted breeding, the SSR marker Rub118b 110 bp allele from Latham was found in resistant germplasm but was not found in any of the susceptible germplasm tested.

Genetic and environmental effects influencing fruit colour and QTL analysis in raspberry

Raspberry (Rubus idaeus) fruit colour was assessed in the Latham x Glen Moy mapping population using a colour meter and visual scores over three seasons and three environments. The colour measurements were found to be significantly associated with pigment content, have high heritability, and stable QTL were identified across environments and seasons. Anthocyanin content has previously been shown to be the major contributor to fruit colour in red raspberry. Major structural genes (F3'H, FLS, DFR, IFR, OMT and GST) and transcription factors (bZIP, bHLH and MYB) influencing flavonoid biosynthesis have been identified, mapped and shown to underlie QTL for quantitative and qualitative anthocyanin composition. Favourable alleles for the selected traits were identified for the aspects of fruit colour and partitioning of individual pigments.

Environmental and seasonal influences on red raspberry anthocyanin antioxidant contents and identification of quantitative traits loci (QTL)

Consumption of raspberries promotes human health through intake of pharmaceutically active antioxidants, including cyanidin and pelargonidin anthocyanins; products of flavonoid metabolism and also pigments conferring colour to fruit. Raspberry anthocyanin contents could be enhanced for nutritional health and quality benefits utilising DNA polymorphisms in modern marker assisted breeding. The objective was to elucidate factors determining anthocyanin production in these fruits. HPLC quantified eight anthocyanin cyanidin and pelargonidin glycosides: -3-sophoroside, -3-glucoside, -3-rutinoside and -3-glucosylrutinoside across two seasons and two environments in progeny from a cross between two Rubus subspecies, Rubus idaeus (cv. Glen Moy)xRubus strigosus (cv. Latham). Significant seasonal variation was detected across pigments less for different growing environments within seasons. Eight antioxidants mapped to the same chromosome region on linkage group (LG) 1, across both years and from fruits grown in field and under protected cultivation. Seven antioxidants also mapped to a region on LG 4 across years and for both growing sites. A chalcone synthase (PKS 1) gene sequence mapped to LG 7 but did not underlie the anthocyanin quantitative traits loci (QTL) identified. Other candidate genes including basic-helix-loop-helix (bHLH), NAM/CUC2-like protein and bZIP transcription factor underlying the mapped anthocyanins were identified.

Mapping QTLs for developmental traits in raspberry from bud break to ripe fruit

Protected cropping systems have been adopted by the UK industry to improve fruit quality and extend the current season. Further manipulation of season, alongside consideration of climate change scenarios, requires an understanding of the processes controlling fruit ripening. Ripening stages were scored from May to July across different years and environments from a raspberry mapping population. Here the interest was in identifying QTLs for the overall ripening process as well as for the time to reach each stage, and principal coordinate analysis was used to summarise the ripening process. Linear interpolation was also used to estimate the time (in days) taken for each plot to reach each of the stages assessed. QTLs were identified across four chromosomes for ripening and the time to reach each stage. A MADS-box gene, Gene H and several raspberry ESTs were associated with the QTLs and markers associated with plant height have also been identified, paving the way for marker assisted selection in Rubus idaeus.