Arabidopsis thaliana AHL family modulates hypocotyl growth redundantly by interacting with each other via the PPC/DUF296 domain

Abstract

The Arabidopsis thaliana genome encodes 29 AT-HOOK MOTIF CONTAINING NUCLEAR LOCALIZED (AHL) genes, which evolved into two phylogenic clades. The AHL proteins contain one or two AT-hook motif(s) and one plant and prokaryote conserved (PPC)/domain of unknown function #296 (DUF296) domain. Seedlings lacking both SOB3/AHL29 and ESC/AHL27 confer a subtle long-hypocotyl phenotype compared with the WT or either single-null mutant. In contrast, the missense allele sob3-6 confers a dramatic long-hypocotyl phenotype in the light. In this study, we examined the dominant-negative feature of sob3-6 and found that it encodes a protein with a disrupted AT-hook motif that abolishes binding to AT-rich DNA. A loss-of-function approach demonstrated different, yet redundant, contributions of additional AHL genes in suppressing hypocotyl elongation in the light. We showed that AHL proteins interact with each other and themselves via the PPC/DUF296 domain. AHLs also share interactions with other nuclear proteins, such as transcription factors, suggesting that these interactions also contribute to the functional redundancy within this gene family. The coordinated action of AHLs requires an AT-hook motif capable of binding AT-rich DNA, as well as a PPC/DUF296 domain containing a conserved Gly-Arg-Phe-Glu-Ile-Leu region. Alteration of this region abolished SOB3/AHL29's physical interaction with transcription factors and resulted in a dominant-negative allele in planta that was phenotypically similar to sob3-6. We propose a molecular model where AHLs interact with each other and themselves, as well as other nuclear proteins, to form complexes which modulate plant growth and development.enhanceosome | seedling establishment

HUA ENHANCER1 Is Involved in Posttranscriptional Regulation of Positive and Negative Regulators in Arabidopsis Photomorphogenesis

“…Five TCPII subfamily transcription factor genes, TCP2, 3, 4, 10, and 24, are known targets of miR319 (Jones-Rhoades et al, 2006). Ectopic expression of TCP2/3/4 with mutated miR319 target sites results in lighthyposensitive phenotypes, so TCP2/3/4 are hypothesized to be negative regulators of hypocotyl elongation (Palatnik et al, 2003;Koyama et al, 2007;Zhao et al, 2013). We confirmed the presence of a miR319-mediated cleaved signature for transcripts of a selected TCPII gene, TCP24, in photomorphogenic Arabidopsis ( Figure 9A).…”

ATAF2 integrates Arabidopsis brassinosteroid inactivation and seedling photomorphogenesis

“…The similarity in binding targets between ATAF2 and AHLs might facilitate their interaction in vivo. AHLs are present in all plant species and are involved in a wide range of biological processes, including the regulation of Arabidopsis hypocotyl growth (Zhao et al, 2013(Zhao et al, , 2014. Together, these observations suggest that ATAF2 and certain AHL proteins might work as functional partners in this fundamental plant development process.…”

“…1A-F). Interestingly, ATAF2 interacts with two members of the AT-hook motifcontaining nuclear-localized (AHL) protein family, which specifically bind A/T-rich DNA (Zhao et al, 2013). The similarity in binding targets between ATAF2 and AHLs might facilitate their interaction in vivo.…”

“…Site-directed mutagenesis of baits was performed using the QuikChange Lightning Kit (Agilent Technologies). His-tagged ATAF2 protein was purified for EMSA by procedures described previously (Zhao et al, 2013).…”

“…Seed sterilization, media composition, plating, growth conditions and hypocotyl measurement were as previously described (Sandhu et al, 2012;Zhao et al, 2013). For BL (Turk et al, 2003), BRZ , IAA (Collett et al, 2000) and NPA (Ruegger et al, 1997) treatment assays, seeds were put on the treatments from the beginning of the experiments.…”