Senescence-associated Barley NAC (NAM, ATAF1,2, CUC) Transcription Factor Interacts with Radical-induced Cell Death 1 through a Disordered Regulatory Domain

Abstract

Background: Plant NAC transcription factors (TF) are important regulators of senescence. Results: Senescence-associated barley HvNAC013 uses intrinsic disorder in transcriptional activation and interactions. Conclusion: Radical induced cell death 1 exploits the intrinsic disorder of HvNAC013 and other TFs for interactions without structure induction in HvNAC013. Significance: This first structural characterization of NAC intrinsic disorder may reveal general features of important TF regulatory interactions.

Multifarious Roles of Intrinsic Disorder in Proteins Illustrate Its Broad Impact on Plant Biology

“…Despite their variable sequences, many of these subgroupspecific conserved motifs have a common feature of being dominated by polar and charged residues with highly conserved hydrophobic or aromatic residues embedded in the polar matrix. Similar arrangements were also found in the barley (Hordeum vulgare) NAC TFs (Kjaersgaard et al, 2011) and, more widely, in the plant-specific GRAS protein family (see next section). Some of these subgroup-specific conserved motifs have been reported to be important for transactivational properties and protein interactions (Taoka et al, 2004;Ko et al, 2007;Kjaersgaard et al, 2011).…”

“…The plant-specific NAC TFs are key regulators of developmental processes (Olsen et al, 2005), abiotic stress responses (Jensen et al, 2010), plant defense (Seo et al, 2010), senescence processes (Kjaersgaard et al, 2011), and xylem formation (Ko et al, 2007). Consistent with the structural modularity of TFs, most NAC proteins have a conserved N-terminal DBD domain, known as the NAC domain, that consists of a twisted b-sheet packed against an a-helix on both sides and binds a consensus core sequence CGT(GA) (Ernst et al, 2004).…”

“…They also have potential capability of disorder-toorder transition through a-helical folding driven by trifluoroethanol (TFE), a reagent that mimics the environment of protein interaction (Kjaersgaard et al, 2011). A motif search of the entire Arabidopsis NAC family revealed that the structurally folded NAC domains of most NAC TFs share five or six highly conserved sequence motifs occurring as either a-helices or b-strands, whereas the intrinsically disordered C-terminal TRDs contain many subgroup-specific conserved motifs, usually spanning between 10 and 20 amino acid residues (Jensen et al, 2010).…”

The Intrinsically Disordered N-terminal Region of AtREM1.3 Remorin Protein Mediates Protein-Protein Interactions

“…1D). The abnormally slow migration of AtREM1.3-N supports the presence of intrinsic disorder within this region (32,33).…”

“…However, only a few plant-signaling components have been experimentally characterized with respect to their ID. Examples of ID proteins are the A. thaliana ERD10 and ERD14 dehydrin proteins (48,49), the N-terminal region of the A. thaliana Hy5 bZIP transcription factor involved in photomorphogenesis (50), and the Hordeum vulgare (barley) senescence-associated NAC transcription factor (33). In the case of the Alb3 membrane insertase (51) and the DELLA proteins (34), their ID regions mediate protein interactions.…”