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Title: Characterization and expression analysis of two cDNAs encoding Xa1 and oxysterol binding proteins in sorghum (Sorghum bicolor)

Author
item PARK, SUNG - Oklahoma State University
item Huang, Yinghua

Submitted to: Academy of Agriculture Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/3/2016
Publication Date: 12/1/2016
Citation: Park, S.J., Huang, Y. 2016. Characterization and expression analysis of two cDNAs encoding Xa1 and oxysterol binding proteins in sorghum (Sorghum bicolor). Academy of Agriculture Journal. 1(4):70-75.

Interpretive Summary: The aphid greenbug (Schizaphis graminum) is a serious pest on important cereal crops in the Great Plains of North America and also considered as a key insect pest of sorghum. Host plant defense plays the critical role in the integrated pest management for sustainable crop production. In this study, we performed experiments to characterize two cDNAs encoding sorghum proteins Xa1 and OSBP, which may be components of the host plant defense against greenbugs. Using northern-blot analysis, the expressions of Xa1 and OSBP genes were verified to be significantly induced only by greenbug infestation and mechanical wounding but were regulated independently from the treatment with jasmonic acid (JA) that is involved in regulation of a majority of plant defense genes in response to attack by chewing insects. These results suggest that both Xa1 and OSBP genes are specifically associated with the defensive responses of sorghum to the juice-sucking greenbug. Further progress in isolation and characterization of novel defense genes against greenbug attack will undoubtedly potentiate to develop greenbug-resistant sorghum cultivars by incorporating the defense genes directly to high-performance cultivars using molecular breeding method.

Technical Abstract: Using suppression subtractive hybridization (SSH) and subsequent microarray analysis, expression profiles of sorghum genes responsive to greenbug phloem-feeding were obtained and identified. Among the profiles, two cDNAs designated to MM73 and MM95 were identified to encode Xa1 (Xa1) and oxysterol binding protein (OSBP), respectively. Further characterization of MM73 and MM95, and the expression analyses of Xa1 and OSBP genes in sorghum were performed in this study. Based on nucleotide sequences of both cDNAs, amino acid sequences were deduced and analyzed. The multiple sequence alignments of deduced amino acid sequences of MM73 and MM95 showed that products of MM73 (125 residues) and MM95 (142 residues) showed high identity in amino acid sequences to Xa1 from sorghum (83%) and OSBP from Arabidopsis (84%), respectively. The expression patterns of Xa1 and OSBP genes in sorghum were analyzed using northern-blot analysis. In response to three different treatments such as greenbug infestation, methyl jasmonate (MeJA) treatment, and mechanical wounding, Xa1 and OSBP genes showed differential expressions exclusively by greenbug infestation and mechanical wounding in a highly similar regulation pattern. However, MeJA treatment showed no effects on regulations of both genes and resulted in the same level of expression to untreated controls, reflecting that regulations of both genes are independent to the octadecanoid pathway involved in jasmonic acid (JA) synthesis, which is known to control diverse defense responses against insect feeding in plants.