Differential expression of genes encoding the phenylpropanoid pathway upon infection of soybean seedlings by Rhizoctonia solani

The impact of Rhizoctonia solani on gene expression of 14 genes and gene homologs encoding key enzymes leading to isoflavone synthesis in the phenylprapanoid pathway was quantified in soybean (Glycine max) seedlings using quantitative reverse transcription polymerase chain reaction. This method allowed accurate quantitative evaluation of expression ratios of genes encoding phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS), chalcone isomerase (CHI), chalcone reductase (CHR), and isoflavone synthase (IFS) in 1-, 2-, and 3-week-old soybean seedlings infected with R. solani and in seedlings that were not infected. Rhizoctonia solani inoculations affected expression ratios of 4 of 14 genes. Compared with control seedlings, a substantial upregulation of CHS 5, CHS 6, and IFS 2 transcript ratios by 34%, 208%, and 226% was observed, respectively. Ratios of the gene encoding CHR were markedly upregulated in infected seedlings at 1 and 2 weeks postinfection with a substantial downregulation 3 weeks after infection. Gene expression was relatively constant for most genes over time, whereas gene expression of a few changed. The findings of the study highlight the necessity of investigating the molecular response of a plant to a pathogen by studying not only an individual gene of the phenylpropanoid pathway but several genes and their gene homologs.