The transcriptional response to salicylic acid plays a role in Fusarium yellows resistance in Brassica rapa L.

Fusarium yellows caused by Fusarium oxysporum f. sp. conglutinans (Foc) is an important disease. Previous studies showed that genes related to salicylic acid (SA) response were more highly induced following Foc infection in Brassica rapa Fusarium yellows resistant lines than susceptible lines. However, SA-induced genes have not been identified at the whole genome level and it was unclear whether they were up-regulated by Foc inoculation. Transcriptome analysis with and without SA treatment in the B. rapa Fusarium yellows susceptible line 'Misugi' and the resistant line 'Nanane' was performed to obtain insights into the relationship between SA sensitivity/response and Fusarium yellows resistance. 'Nanane's up-regulated genes were related to SA response and down-regulated genes were related to jasmonic acid (JA) or ethylene (ET) response, but differentially expressed genes in 'Misugi' were not. This result suggests that Fusarium yellows resistant and susceptible lines have a different SA response and that an antagonistic transcription between SA and JA/ET responses was found only in a Fusarium yellows resistant line. SA-responsive genes were induced by Foc inoculation in Fusarium yellows resistant (RJKB-T23) and susceptible lines (RJKB-T24). By contrast, 39 SA-induced genes specific to RJKB-T23 might function in the defense response to Foc. In this study, SA-induced genes were identified at the whole genome level, and the possibility, the defense response to Foc observed in a resistant line could be mediated by SA-induced genes, is suggested. These results will be useful for future research concerning the SA importance in Foc or other diseases resistance in B. rapa.