Annotation of Cultivar Variations at the Multigeneic Rhg1/Rfs2 Locus: Polymorphisms Underling AlteraAnnotation of Cultivar Variations at the Multigeneic Rhg1/Rfs2 Locus: Polymorphisms Underling Alterations of Root Development and Pest Resistancetions of Root Development and Pest Resistance

Soybean (Glycine max (L.) Merr.) suffers yield loss due to root infection from soil infestation by Heterodera glycine I. (soybean cyst nematode SCN) and Fusarium virguliforme (Aoki; sudden death syndrome (SDS)). The major locus for SCN and SDS resistance has previously been identified as Rhg1/Rfs2 (chr18; LG G) (site reference). The objective of this experiment was to compare the Sanger DNA sequence of a resistant cultivar (‘Forrest’) and two susceptible cultivars (‘Williams 82’ and ‘Asgrow A3244’). Sequences were downloaded from GenBank for Williams 82, Phytzome for A3244 and a newly sequenced BAC-B73P06 (82,157 bp) encompassing the Rfs2/Rhg1 locus. Using the resistant cultivars, 800 single nucleotide polymorphisms (SNPs) and 57 indels were identified. In contrast, the susceptible cultivars had just 12 SNPs and no indels between them. Polymorphisms were clustered within 59 kbp, divided into three sections. There were 5 predicted recombination breakpoints. The third and fourth breakpoints were located before gene 3 and after gene 5 (Glyma18g02680; the RLK at Rhg1/Rfs2) which were therefore inferred to be derived from Peking, within the Rhg1/Rfs2 region. Comparisons of SNPs identified in Illumina sequences from 31 semi-domesticated genomes showed 80% of the total SNPs in Forrest were found among the genomes. Annotation and gene prediction showed the BAC gene prediction encoded 9-10 genes. There were 31 SNPs within exons and 137 among introns. Just 11 SNPs caused amino acid changes. There were 5 SNPs in cis regulatory elements (CREs) and 14 in promoters. Polymorphisms indicated the regions that were introgressed from Peking had defined limits. Proteins across the region were highly conserved compared to non-coding regions, suggesting purifying selection occurred

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