Genetic, Genomic, and Gene Expression Analyses of Soybean Aphid Resistance Genes

The soybean aphid (Aphis glycines Matsumura) has become a major pest on soybean [Glycine max (L.) Merr.] after it was first found in the United States in 2000. Genetic sources of resistance to the aphid were identified in the plant introductions (PIs) and US cultivars. In our soybean breeding and genetics program at Michigan State University, soybean aphid resistance genes rag1c and rag4 in PI567541B, were mapped to the soybean chromosome 7 (LG M) and chromosome 13 (LG F), respectively. rag1c gene was then fine mapped in a 96 kbp interval flanked by SNP markers MSUSNP7-32 and MSUSNP7-20 while rag4 gene was fine mapped between MSUSNP13-5 and MSUSNP13-7 with a 39.3 kb interval. Very little is known about the expression and function of the candidate soybean aphid resistance genes within these genomic regions. Objectives of this study were to analyze the sequences and expression of candidate rag1c and rag4 genes and gain insight into the molecular basis of the compatible interaction between soybean host and soybean aphid based on our time-course transcriptomic study of soybean aphid resistance. To determine if the regulations of gene expression in the loci were correlated with soybean resistance to the aphid, the global gene expression was measured to quantify the gene expression levels of soybean tissues challenged by the soybean pest. In turn, the candidate genes were found to possess unique expression patterns during host-pest interactions in the fine mapped intervals. Among them, two candidate genes displayed a strong association with the resistance phenotype in both temporal and spatial fashions.