AtNFXL1, an Arabidopsis homologue of the human transcription factor NF-X1, functions as a negative regulator of the trichothecene phytotoxin-induced defense response

Trichothecenes are a closely related family of phytotoxins that are produced by phytopathogenic fungi. In Arabidopsis, expression of AtNFXL1, a homologue of the putative human transcription repressor NF-X1, was significantly induced by application of type A trichothecenes, such as T-2 toxin. An atnfxl1 mutant growing on medium lacking trichothecenes showed no phenotype, whereas a hypersensitivity phenotype was observed in T-2 toxin-treated atnfxl1 mutant plants. Microarray analysis indicated that several defense-related genes (i.e. WRKYs, NBS-LRRs, EDS5, ICS1, etc.) were upregulated in T-2toxin-treated atnfxl1 mutants compared with wildtype plants. In addition, enhanced salicylic acid (SA) accumulation was observed in T-2 toxin-treated atnfxl1 mutants, which suggests that AtNFXL1 functions as a negative regulator of these defense-related genes via an SA-dependent signaling pathway. We also found that expression of AtNFXL1 was induced by SA and flg22 treatment. Moreover, the atnfxl1 mutant was less susceptible to a compatible phytopathogen, Pseudomonas syringae pv. tomato strain DC3000 (Pst DC3000). Taken together, these results indicate that AtNFXL1 plays an important role in the trichothecene response, as well as the general defense response in Arabidopsis.