NAC genes: Time-specific regulators of hormonal signaling in Arabidopsis

Environmental stresses on both animals and plants impose massive transcriptional perturbations. Successful adaptations to such stresses are being orchestrated by both activating and repressing effects of transcription factors on specific target genes. We have recently published a systematic characterization of members of the large NAC gene transcription factor family in the model weed Arabidopsis thaliana. Our analysis revealed interesting sub-groupings of the Arabidopsis NAC genes, relating structure and function. Here we present a meta-analysis revealing distinct temporal expression profiles of NAC genes upon stimuli with seven phytohormones. Our analysis could be a first indication of NAC-centered transcriptional networks, which coordinate timely hormonal signaling in plants

The Arabidopsis thaliana NAC transcription factor family: structure-function relationships and determinants of ANAC019 stress signalling

International audienceTranscription factors (TFs) are modular proteins minimally containing a DNA-binding domain (DBD) and a transcription regulatory domain (TRD). NAC proteins comprise one of the largest plant TF-families. They are key regulators of stress perception and developmental programs, and most share an N-terminal NAC domain. Based on analyses of gene expression data and phylogeny of Arabidopsis thaliana NAC TFs we systematically decipher structural and functional specificities of the conserved NAC domains and divergent C-termini. Nine of ten NAC domains analyzed bind a previously identified NAC DNA-target sequence with a CGT[GA] core, although with different affinities. Likewise, all but one of the NAC proteins analyzed is dependent on the C-terminal region for transactivational activity. In silico analyses show that NAC TRDs contain group-specific sequence motifs and are characterized by a high degree of intrinsic disorder. Furthermore, ANAC019 was identified as a new positive regulator of abscisic acid (ABA)-signaling, conferring ABA-hypersensitivity when ectopically expressed in plants. Interestingly, ectopic expression of ANAC019 DBD or TRD alone also resulted in ABA-hypersensitivity. Expression of stress-responsive marker genes (COR47, RD29b, ERD11) was also induced by full-length and truncated ANAC019. Domain-swapping was used to analyze the specificity of this function. Replacement of the NAC domain of ANAC019 with analogous regions of other NAC TFs resulted in chimeric proteins, which also have the ability to regulate ABA-signaling positively. In contrast, replacing the ANAC019 TRD with other TRDs abolished ANAC019-mediated ABA-hypersensitivity. In conclusion, our results demonstrate that biochemical and functional specificity is associated with both DBDs and TRDs in NAC TFs

Senescence-associated barley NAC (NAM, ATAF1,2, CUC) transcription factor interacts with radical-induced cell death 1 through a disordered regulatory domain

Senescence in plants involves massive nutrient relocation and age-related cell death. Characterization of the molecular components, such as transcription factors (TFs), involved in these processes is required to understand senescence. We found that HvNAC005 and HvNAC013 of the plant-specific NAC (NAM, ATAF1,2, CUC) TF family are up-regulated during senescence in barley (Hordeum vulgare). Both HvNAC005 and HvNAC013 bound the conserved NAC DNA target sequence. Computational and biophysical analyses showed that both proteins are intrinsically disordered in their large C-terminal domains, which are transcription regulatory domains (TRDs) in many NAC TFs. Using motif searches and interaction studies in yeast we identified an evolutionarily conserved sequence, the LP motif, in the TRD of HvNAC013. This motif was sufficient for transcriptional activity. In contrast, HvNAC005 did not function as a transcriptional activator suggesting that an involvement of HvNAC013 and HvNAC005 in senescence will be different. HvNAC013 interacted with barley radical-induced cell death 1 (RCD1) via the very C-terminal part of its TRD, outside of the region containing the LP motif. No significant secondary structure was induced in the HvNAC013 TRD upon interaction with RCD1. RCD1 also interacted with regions dominated by intrinsic disorder in TFs of the MYB and basic helix-loop-helix families. We propose that RCD1 is a regulatory protein capable of interacting with many different TFs by exploiting their intrinsic disorder. In addition, we present the first structural characterization of NAC C-terminal domains and relate intrinsic disorder and sequence motifs to activity and protein-protein interactions