Development of a pooled probe method for locating small gene families in a physical map of soybean using stress related paralogues and a BAC minimum tile path

Structure, expression profile and phylogenetic inference of chalcone isomerase-like genes from the narrow-leafed lupin (Lupinus angustifolius L.) genome

Lupins, like other legumes, have a unique biosynthesis scheme of 5-deoxy-type flavonoids and isoflavonoids. A key enzyme in this pathway is chalcone isomerase (CHI), a member of CHI-fold protein family, encompassing subfamilies of CHI1, CHI2, CHI-like (CHIL), and fatty acid-binding (FAP) proteins. Here, two Lupinus angustifolius (narrow-leafed lupin) CHILs, LangCHIL1 and LangCHIL2, were identified and characterized using DNA fingerprinting, cytogenetic and linkage mapping, sequencing and expression profiling. Clones carrying CHIL sequences were assembled into two contigs. Full gene sequences were obtained from these contigs, and mapped in two L. angustifolius linkage groups by gene-specific markers. Bacterial artificial chromosome fluorescence in situ hybridization approach confirmed the localization of two LangCHIL genes in distinct chromosomes. The expression profiles of both LangCHIL isoforms were very similar. The highest level of transcription was in the roots of the third week of plant growth; thereafter, expression declined. The expression of both LangCHIL genes in leaves and stems was similar and low. Comparative mapping to reference legume genome sequences revealed strong syntenic links; however, LangCHIL2 contig had a much more conserved structure than LangCHIL1. LangCHIL2 is assumed to be an ancestor gene, whereas LangCHIL1 probably appeared as a result of duplication. As both copies are transcriptionally active, questions arise concerning their hypothetical functional divergence. Screening of the narrow-leafed lupin genome and transcriptome with CHI-fold protein sequences, followed by Bayesian inference of phylogeny and cross-genera synteny survey, identified representatives of all but one (CHI1) main subfamilies. They are as follows: two copies of CHI2, FAPa2 and CHIL, and single copies of FAPb and FAPa1. Duplicated genes are remnants of whole genome duplication which is assumed to have occurred after the divergence of Lupinus, Arachis, and Glycine.

The receptor like kinase at Rhg1-a/Rfs2 caused pleiotropic resistance to sudden death syndrome and soybean cyst nematode as a transgene by altering signaling responses

BACKGROUND

Soybean (Glycine max (L. Merr.)) resistance to any population of Heterodera glycines (I.), or Fusarium virguliforme (Akoi, O'Donnell, Homma & Lattanzi) required a functional allele at Rhg1/Rfs2. H. glycines, the soybean cyst nematode (SCN) was an ancient, endemic, pest of soybean whereas F. virguliforme causal agent of sudden death syndrome (SDS), was a recent, regional, pest. This study examined the role of a receptor like kinase (RLK) GmRLK18-1 (gene model Glyma_18_02680 at 1,071 kbp on chromosome 18 of the genome sequence) within the Rhg1/Rfs2 locus in causing resistance to SCN and SDS.

RESULTS

A BAC (B73p06) encompassing the Rhg1/Rfs2 locus was sequenced from a resistant cultivar and compared to the sequences of two susceptible cultivars from which 800 SNPs were found. Sequence alignments inferred that the resistance allele was an introgressed region of about 59 kbp at the center of which the GmRLK18-1 was the most polymorphic gene and encoded protein. Analyses were made of plants that were either heterozygous at, or transgenic (and so hemizygous at a new location) with, the resistance allele of GmRLK18-1. Those plants infested with either H. glycines or F. virguliforme showed that the allele for resistance was dominant. In the absence of Rhg4 the GmRLK18-1 was sufficient to confer nearly complete resistance to both root and leaf symptoms of SDS caused by F. virguliforme and provided partial resistance to three different populations of nematodes (mature female cysts were reduced by 30-50%). In the presence of Rhg4 the plants with the transgene were nearly classed as fully resistant to SCN (females reduced to 11% of the susceptible control) as well as SDS. A reduction in the rate of early seedling root development was also shown to be caused by the resistance allele of the GmRLK18-1. Field trials of transgenic plants showed an increase in foliar susceptibility to insect herbivory.

CONCLUSIONS

The inference that soybean has adapted part of an existing pathogen recognition and defense cascade (H.glycines; SCN and insect herbivory) to a new pathogen (F. virguliforme; SDS) has broad implications for crop improvement. Stable resistance to many pathogens might be achieved by manipulation the genes encoding a small number of pathogen recognition proteins.

Use of chromosome walking in discovery of single-nucleotide polymorphism in noncoding regions of a candidate actin gene in Pinus radiata

Untranslated regions (UTRs) of eukaryotic mRNAs play crucial roles in post-transcriptional regulation of gene expression via the modulation of nucleocytoplasmic mRNA transport, translation efficiency, subcellular localization, and message stability. Single-nucleotide polymorphisms (SNPs) in UTRs of a candidate gene may also change the post-transcriptional regulation of a gene or function by nucleotide mutation. For species that have not been entirely sequenced genomically, new methods need to be devised to discover SNPs in noncoding regions of candidate genes. In this study, based on the expressed sequence tag (EST) of Pinus radiata (Monterey pine), we obtained all the sequences of UTRs of the actin gene by using a chromosome walking method. We also detected all the SNPs in and around the coding region of the actin gene. In this way, the full genomic sequence (2154 bp) of the actin gene was identified, including the 5’UTR, introns, the coding sequence, and the 3’UTR. PCR amplification and DNA fragment sequencing from 200 unrelated P. radiata trees revealed a total of 21 SNPs in the actin gene, of which 3 were located in the 5’UTR, 3 in the introns, 10 in the coding sequence, and 5 in the 3’UTR. We show that chromosome walking can be used for obtaining the sequence of UTRs, and then, based on this sequence, to discover SNPs in the noncoding regions of candidate genes from this species without an entire genomic sequence.

Re-annotation of the physical map of Glycine max for polyploid-like regions by BAC end sequence driven whole genome shotgun read assembly

BACKGROUND

Many of the world's most important food crops have either polyploid genomes or homeologous regions derived from segmental shuffling following polyploid formation. The soybean (Glycine max) genome has been shown to be composed of approximately four thousand short interspersed homeologous regions with 1, 2 or 4 copies per haploid genome by RFLP analysis, microsatellite anchors to BACs and by contigs formed from BAC fingerprints. Despite these similar regions,, the genome has been sequenced by whole genome shotgun sequence (WGS). Here the aim was to use BAC end sequences (BES) derived from three minimum tile paths (MTP) to examine the extent and homogeneity of polyploid-like regions within contigs and the extent of correlation between the polyploid-like regions inferred from fingerprinting and the polyploid-like sequences inferred from WGS matches.

RESULTS

Results show that when sequence divergence was 1-10%, the copy number of homeologous regions could be identified from sequence variation in WGS reads overlapping BES. Homeolog sequence variants (HSVs) were single nucleotide polymorphisms (SNPs; 89%) and single nucleotide indels (SNIs 10%). Larger indels were rare but present (1%). Simulations that had predicted fingerprints of homeologous regions could be separated when divergence exceeded 2% were shown to be false. We show that a 5-10% sequence divergence is necessary to separate homeologs by fingerprinting. BES compared to WGS traces showed polyploid-like regions with less than 1% sequence divergence exist at 2.3% of the locations assayed.

CONCLUSION

The use of HSVs like SNPs and SNIs to characterize BACs wil improve contig building methods. The implications for bioinformatic and functional annotation of polyploid and paleopolyploid genomes show that a combined approach of BAC fingerprint based physical maps, WGS sequence and HSV-based partitioning of BAC clones from homeologous regions to separate contigs will allow reliable de-convolution and positioning of sequence scaffolds (see BES_scaffolds section of SoyGD). This approach will assist genome annotation for paleopolyploid and true polyploid genomes such as soybean and many important cereal and fruit crops.

Mapping two genes in the purine metabolism pathway of soybean

Mapping genes in biochemical pathways allow study of the genomic organization of pathways and geneic relationships within these pathways. Additionally, molecular markers located within the boundaries of a specific gene sequence represent important marker assisted selection resources. We report map locations of two geneic markers from the purine synthesis pathway in soybean (Glycine max (L. merr.)), utilizing a 90 plant F(2) population created from the cross of "DT97-4290" x "DS97-84-1". Primers were designed based on sequences from annotated soybean complimentary DNA. A polymorphic, co-dominant, sequence-characterized amplified region marker was created for hypoxanthine phosphoribosyl transferase (EC 2.4.2.8). Linkage analysis placed this gene on linkage group (LG) O. In addition, a single-nucleotide polymorphism (SNP) marker was developed for a urate oxidase gene (EC 1.7.3.3). Linkage analysis of the SNP placed the urate oxidase gene on LG I. For both genes, amplicon sequence data confirmed the identification of the respective gene. Mapping these genes represents the first step in understanding the genomic organization of the purine biochemical pathway in soybean.