Submitted to: American Peanut Council Meeting
Publication Type: Abstract Only
Publication Acceptance Date: February 16, 2009
Publication Date: March 1, 2009
Citation: Guo, B., 2009. Peanut EST Genomics Project: Identification and characterization of molecular marker(s) associated with resistance to TSWV and white mold in peanuts [abstract]. Proceedings from the American Peanut Council/Peanut Foundationa Annual Meeting, March 10-11,2009, Washington, DC. Technical Abstract: Peanut is vulnerable to a range of diseases, such as tomato spotted wilt virus (TSWV), early (Cercospora arachidicola) and late (Cercosporidium personatum) leaf spots, and southern stem rot/white mold (Sclerotium rolfsii). In peanut production areas in the southeastern U.S., tomato spotted wilt virus disease caused by tomato spotted wilt tospovirus (TSWV) has become more prevalent and more severe. White mold also is a common and often destructive disease of peanut. The most promising solution for managing peanut diseases is using resistant cultivars. Tifrunner has been released as a resistant cultivar to TSWV and leaf spots. New breeding line NC94022 (botanical variety hirsuta) has been identified with higher resistance to TSWV. A cultivar having disease resistance and high yield would present tremendous advantages for peanut growers to remain competitive. Our strategy is to identify resistance genes and molecular markers associated with disease resistance and develop resistant peanut cultivars by using marker-assistant breeding and selection. Progress has been made in 2008: We have identified and sequenced two putative TSWV resistance genes, Ahsw1 and Ahsw2, and two peanut superoxidase dismutase (SOD) or oxalate oxidase (OxO) germin-like genes, AhGERLand AhGERS. Two mapping populations with 248 and 356 RILs (recombinant inbred lines) are in F5 generation in Purto Rico Winter Nursery. Germin and germin-like protein (GLP) genes are members of large multigene families. These genes have been reported to play a role directly or indirectly in plant defense response. A number of GLPs have been demonstrated to have superoxidase dismutase (SOD) or oxalate oxidase (OxO) activity leading to production of hydrogen peroxide. Two peanut germin-like genes, AhGERLand AhGERS, were obtained from cDNA libraries. The AhGERL including 991 bp cDNA sequences encodes a 219 amino acid protein with a 21-residue signal peptide. After cleavage of the signal peptide, it has a mass of 20.84 kDa. The AhGERS comprised of 744 bp cDNA encodes a protein with 220 amino acid residues containing a putative signal peptide of 24 residues, with a mass of 20.63 kDa after removal of the signal peptide. The two proteins both contain three motifs, Q/NDL/FCVAD, G(X)5HXH(X) 11G and G(X)5P(X) 4H(X) 3N, which are characteristic to germin-like proteins. Searches of GenBank database indicate that AhGERL and AhGERS, exhibit respectively up to 76% and 82% amino acid identity to certain plant germin-like proteins. Southern blot analysis showed that the two genes possibly exist as at least four copies in the peanut genome. Northern blots conducted with total RNA from leaves, seeds and roots tissues indicated that AhGERL is mainly expressed in peanut leaves. Enzyme assay indicated that the coding sequence of AhGERL exhibited superoxide dismutase activity but no detectable oxalate oxidase activity, while neither activity was detected for AhGERS (because of the expressed protein not released from protein body). The SOD activity of AhGERL was less sensitive to hydrogen peroxide than SOD from horseradish, suggesting it to be copper/zinc-containing SOD (Cu/ZnSOD). The pET-AhGERL tranformed E.coli exhibited higher SOD activity and tolerance to paraquat-mediated growth inhibition compared to empty vector (pET-28a) transformed cells, indicating that AhGERL conferred resistance to oxidative stress.