Regulation of the Cytochrome P450 Gene, CYP81D11, in Arabidopsis thaliana, Subjected to Chemical Stress

In higher plants, toxic chemicals induce the expression of a set of detoxification genes. In Arabidopsis thaliana, transcriptional activation of a subset of these depends on Class II TGA transcription factors and the TGA-interacting GRAS protein SARECROW-LIKE 14 (SCL14). The TGA2,5,6/SCL14-activated cytochrome P450 gene CYP81D11 has been detected in a number of microarray analyses as being highly responsive to treatments with different reactive chemicals, like the auxin transport inhibitor 2,3,5-triiodobenzoic acid (TIBA), the allelocemical benzoxazolin-2(3H)-one (BOA), the explosive 2,4,6-trinitrotoluene (TNT) and phytoprostanes (highly reactive compounds generated by non-enzymatic lipid oxidation processes). In contrast to other known TGA2,5,6/SCL14-dependent genes, CYP81D11 is inducible by the plant hormone methyl jasmonate (MeJA), which is a precursor of the active hormone jasonate-isoleucine (JA-Ile) that specifically binds to the receptor/co-activator complex CORONATINE INSENSITIVE1 (COI1)/JAZ. In this thesis, we demonstrate that three distinct mechanisms of COI1 action merge on the CYP81D11 promoter: (i) the well-established function that leads to the activation of MYC2 upon action of COI1 by elevated JA-Ile levels after MeJA and pathogen treatment; (ii) a novel function that requires basal JA-Ile levels, the transcriptional activator MYC2, a MYC2 binding site in the promoter and functional JAZ repressors; and (iii) as second novel function that is independent from all the known components of COI1-dependent signalling including the ligand JA-Ile. Whole genome microarray analysis of TIBA-treated wild-type and coi1 plants revealed that 73 genes are induced only in the presence of COI1. Real-time RT-PCR and hierarchical cluster analysis indicated that the JA-Ile-independent COI1 function is likely to be unique for the CYP81D11 promoter under these conditions. In contrast, COI1 is important for the expression of a large set of genes even although JA-Ile levels do not increase. While COI1 positively regulates CYP81D11, overexpression of the two NAC transcription factors ATAF1 and ANAC032 negatively effects CYP81D11 expression after TIBA as well as after MeJA treatment.