WRKY11 up-regulated dirigent expression to enhance lignin/lignans accumulation in Lilium regale Wilson during response to Fusarium wilt

Lilium are highly economically valuable ornamental plants that are susceptible to Fusarium wilt caused by Fusarium oxysporum. Lilium regale Wilson, a wild lily native to China, is highly resistant to F. oxysporum. In this study, a WRKY transcription factor, WRKY11, was isolated from L. regale, and its function during the interaction between L. regale and F. oxysporum was characterized. The ectopic expression of LrWRKY11 in tobacco increased the resistance to F. oxysporum, moreover, the transcriptome sequencing and UHPLC-MS/MS analysis indicated that the methyl salicylate and methyl jasmonate levels rose in LrWRKY11 transgenic tobacco, meanwhile, the expression of lignin/lignans biosynthesis-related genes including a dirigent (DIR) was up-regulated. The lignin/lignans contents in LrWRKY11-transgenic tobacco also significantly increased compared with the wild-type tobacco. In addition, the resistance of L. regale scales in which LrWRKY11 expression was silenced by RNAi evidently decreased, and additionally, the expression of lignin/lignans biosynthesis-related genes including LrDIR1 was significantly suppressed. Therefore, LrDIR1 and its promoter (PLrDIR1) sequence containing the W-box element were isolated from L. regale. The interaction assay indicated that LrWRKY11 specifically bound to the W-box element in PLrDIR1 and activated LrDIR1 expression. Additionally, β-glucuronidase activity in the transgenic tobacco co-expressing LrWRKY11/PLrDIR1-β-glucuronidase was higher than that in transgenic tobacco expressing PLrDIR1-β-glucuronidase alone. Furthermore, the ectopic expression of LrDIR1 in tobacco enhanced the resistance to F. oxysporum and increased the lignin/lignans accumulation. In brief, this study revealed that LrWRKY11 positively regulated L. regale resistance to F. oxysporum through interaction with salicylic acid/jasmonic acid signaling pathways and modulating LrDIR1 expression to accumulate lignin/lignans.