The role of salicylic acid responsive genes in disease resistance in Brassica rapa vegetable

Salicylic acid (SA) is a plant hormone that regulates many stress responses and developmental processes including the plant immune response, thermogenesis, senescence, and abiotic stress responses. To identify SA responsive genes at the whole genome level, we performed RNA-sequencing analysis with and without SA treatment in two komatsuna cultivars (Brassica rapa var. perviridis). We identified 1,061 up- and 994 downregulated genes that overlapped between the two cultivars, and these genes were defined as B. rapa SA-induced genes (BrSAIGs) and B. rapa SA-suppressed genes (BrSASGs), respectively. In this study, we identified genes overlapping between BrSAIGs/BrSASGs and paired genes overlapping natural antisense transcripts (NATs) or intronic noncoding RNAs (incRNAs) in their encoding regions. Thirty-three mRNA/NAT pairs and three mRNA/incRNA pairs were identified. The transcriptional relationship between mRNAs and their paired NATs following SA treatment was examined, and two of four pairs showed a positive association of expression levels between mRNAs and their paired NATs. These results suggest that the transcriptional association of mRNAs and their paired NATs plays a role in SA response. Previously, SA treatment was performed by adding SA to the solid medium, but this method has limitations on the number of samples that can be assayed simultaneously. In this study, we sprayed SA on the samples, which is more high-throughput. The upregulation of all six genes that were shown to be upregulated following SA treatments on the medium, was found following spraying. Transcriptional induction was faster with SA spraying than by adding SA into the medium. These results indicate that SA spraying is applicable for further experiments.