Recombination suppression at the dominant Rhg1/Rfs2 locus underlying soybean resistance to the cyst nematode

Abstract

Host resistance to "yellow dwarf" or "moonlight" disease cause by any population (Hg type) of Heterodera glycines I., the soybean cyst nematode (SCN), requires a functional allele at rhg1. The host resistance encoded appears to mimic an apoptotic response in the giant cells formed at the nematode feeding site about 24-48 h after nematode feeding commences. Little is known about how the host response to infection is mediated but a linked set of 3 genes has been identified within the rhg1 locus. This study aimed to identify the role of the genes within the locus that includes a receptor-like kinase (RLK), a laccase and an ion antiporter. Used were near isogeneic lines (NILs) that contrasted at their rhg1 alleles, gene-based markers, and a new Hg type 0 and new recombination events. A syntenic gene cluster on Lg B1 was found. The effectiveness of SNP probes from the RLK for distinguishing homolog sequence variants on LgB1 from alleles at the rhg1 locus on LgG was shown. The resistant allele of the rhg1 locus was shown to be dominant in NILs. None of the recombination events were within the cluster of the three candidate genes. Finally, rhg1 was shown to reduce the plant root development. A model for rhg1 as a dominant multi-gene resistance locus based on the developmental control was inferred.

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

“…At the other 2 residues the changes were identical to the susceptible alleles of Essex and Williams 82. From sequence comparison and transcript abundances it appears likely the paralogs GmRLK18-1 and GmRLK11-1 would share functions and should hetero-dimerize [47]. …”

“…Perhaps the failure to recombine within the central 3 gene cluster caused the unusually high frequency of heterozygous plants in the neighboring region. A potential suppressor locus acting on the resistance allele of Rhg1 was identified earlier [21,45,47]. The allele of the gene on chromosome 7 (Lg M) had to be inherited from the resistant parent to prevent zygote or embryo lethality in SCN resistant plants.…”

“…For detection of mRNA products of GmRLK18-1 (Figure 3) the qRT-PCR methods described previously [45-47] were followed. Briefly, mRNA concentrations were estimated from Cot curve analyses using cDNAs.Actin1 was the control used for comparisons.…”

“…How the root reduction contributes to resistance may involve a locus on chromosome 7 (LG M) where Rzd , an interacting allele needed for r esistance to z ygote d eath, was strictly co-inherited in phase with Rhg1/Rfs2 -a [21]. Therefore, effects on development were predicted for the gene(s) underlying Rhg1-a/Rfs2-a [16,43-47]. …”

Nematode Resistance in Soybean

“…For example, the HG Type of a SCN field population is described as 2.5.7, meaning this SCN population is virulent on three indicator lines, PI 88788 (2), PI 209332 (5), and PI 548316 (7), with FI values greater than 10%. Recently, the HG Types classification scheme has been commonly used in various genetic studies of SCN (Afzal et al 2012;Arelli et al 2009;Vuong et al 2010Vuong et al , 2011Wu et al 2009). …”