2013 Annual Report
1a.Objectives (from AD-416):
Fine mapping, metabolomics and transcriptomics of genes for soybean aphid resistance.
1b.Approach (from AD-416):
Recombinant inbred line (RIL) populations and near isogenic lines (NILs) will be used for conducting the fine mapping, metabolomics, transcriptomics and proteomics studies with help from collaborators.
The metabolomics study with Rag5 and Rag2 near isogenic lines (NILs) was completed, data were analyzed and a manuscript was submitted for journal review. Rag2 resistance clearly correlated to two specific triterpenoid saponins, tentatively identified as Soyasaponin Ag (Sap Ag) and deacetylated Soyasaponin Bd (Sap Bd-deAc); these were 5 and 8 fold higher, respectively, in the Rag2 resistant than susceptible NIL. Of particular interest, Sap Ag was undetectable in Wyandot, the susceptible parent of the NILs. Interestingly, it was also induced upon aphid infestation of the NILs. Rag5 resistance clearly correlated to three specific kaempferol glycosides, including K3 (a gentiobioside), K4 (a triglycoside containing gentiobose and rhamnose) and K9 (a triglucoside containing both gentiobiose and sophorose linkages). Of particular interest was K9, which was 7 fold higher in the Rag5 resistant NIL than susceptible NIL and 58 fold higher in the Rag5 resistant NIL than in Wyandot. In aphid infested tissues, K5 (a simple glucoside) and K3 accumulated. K5 and K3 are both precursors of K4 and K9. Accumulations of the saponins and kaempferol glycosides upon aphid infestation may suggest some genetic adaptation within the plant-aphid interactions.
Nearly, 200 kilobases in the Rag5 region of two parental lines is being sequenced after amplifying with long range PCR (10-15kb each). SNP markers will be identified in the region and NILs will be genotyped to identify recombinants to further fine map the Rag5 region. The transcriptomic study on the Rag5 NILs is in progress. RNAs were extracted from leaf tissues collected at five time points (0, 8, 16, 24 and 48 hrs) after infestation of soybean seedlings with the soybean aphid biotype 2. This project relates to and expands on objective 2B (Genetic characterization and molecular mapping of aphid resistance genes) of the parent project.