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Title:   Author  item
                                            Lewers, Kimberlyitem
                                            HEINZ, RUTHitem
                                            Beard, Hunteritem
                                            MAREK, LAURA - IOWA STATE UNIVERSITYitem
                                            Matthews, Benjamin

                                                         - *Ben*
  Submitted to: Plant Molecular Biology
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 6/25/2001
                                    Publication  Date: N/A
                                    Citation: N/AInterpretive Summary:   The soybean cyst nematode is the major pest of soybean and causes an   estimated 1.5 billion dollars loss to the soybean crop in the U.S. each   year.  We physically isolated a large genomic DNA sequence from the   soybean cultivar Williams 82 which is susceptible to the soybean cyst   nematode.  The isolated DNA region resides close to the Rhg4 locus, one    of the genes that confer resistance to the soybean cyst nematode race 3   in resistant soybean cultivars.  The genomic DNA was subcloned as   smaller pieces and portions of the DNA were sequenced and mapped to   provide landmarks throughout the clone.  The DNA sequences were compared   to sequences in computer databases to determine their similarity to   known genes.  Several DNA sequnces had high similarity to known genes,   such as chalcone synthase and peroxidase.  These landmarks will be   useful to researchers as probes to identify and order clones from a    soybean cultivar resistant to soybean cyst nematode attack.  Then DNA   sequences from this region can be compared between soybean cultivars   that are sensitive and those that are resistant to attack by the soybean   cyst nematode.  This information will be used by scientists to identify   the gene responsible for conferring resistance to the soybean cyst   nematode and will enable soybean breeders to develop soybean cultivars   with better resistance to this nematode.
                                Technical Abstract:  Soybean (Glycine max L. Merrill) Linkage Group A2 contains a major  resistance gene to the soybean cyst nematode (Heterodera glycines  Ichinohe) at the Rhg4 locus near a gene encoding aspartokinase homoserine  dehydrogenase (AK-HSDH) and also near the I locus affecting seed coat  color.  A PCR assay using primers designed from a gene encoding AK-HSDH   was used to screen approximately 40,000 clones from a bacterial artificia  chromosome (BAC) library constructed from genomic DNA of the susceptible  cultivar Williams 82 to physically isolate the Rhg4 genomic region.  The  BACs identified by the screen were assayed by PCR using primers designed  from DNA sequence associated with the I locus.  Only BAC Gm_ISb001_056_G02  (56G2) was positive for both assays.  BAC 56G2, used as a probe against a  library of cDNA clones from infected resistant soybean, identified cDNA  clones having high sequence similarity to genes encoding chalcone   synthase, peroxidase, benzoyl transferase, and a ribosomal protein.  EcoR  I subclones of the BAC had high sequence similarity to genes encoding AK-  HSDH, chalcone synthase, glucosyl-transferase, a heat shock transcription  factor, a membrane-associated salt-inducible protein, adenosyl  homocysteinase, an RNA-binding protein, a protein kinase, and a G10-like  protein.  These genes provide landmarks to identify BAC clones near the  Rhg4 locus in resistant soybean genomic libraries and provide a foundation  for comparison of SCN resistant and susceptible DNA sequences in this  region.  Observed duplication on both the gene level and the regional  level within this BAC may be responsible for reported organizational  instability in this part of the genome.


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