title: PICKLE is required for SOLITARY-ROOT/IAA14-mediated repression of ARF7 and ARF19 activity during Arabidopsis lateral root initiation.
abstract: Lateral root (LR) formation in Arabidopsis is regulated by auxin signaling through AUXIN RESPONSE FACTOR transcriptional activators, ARF7 and ARF19, and auxin/indole-3-acetic acid (Aux/IAA) repressors, including SOLITARY-ROOT (SLR)/IAA14. Previous studies have strongly suggested that, in the gain-of-function slr-1 mutant, stabilized mutant IAA14 (mIAA14) protein inactivates ARF7/19 functions, thereby completely blocking LR initiation. However, the mechanism of inactivation is still unknown. We have now identified an extragenic suppressor mutation of slr-1, suppressor of slr2 (ssl2), which specifically restores LR formation in the slr-1 mutant, and have found that SSL2 negatively regulates the auxin-induced pericycle cell divisions required for LR initiation. The SSL2 gene encodes PICKLE (PKL), a homologue of the animal chromatin-remodeling factor CHD3/Mi-2, and LR formation restored in pkl/ssl2 slr-1 mutants depends on ARF7/19 functions, suggesting that ARF7/19-dependent transcription takes place if there is a pkl/ssl2 mutation in slr-1. In animals, Mi-2 represses transcription as a subunit of the NuRD/Mi-2 complex containing histone deacetylases (HDACs). Inhibition of HDAC activity by trichostatin A also results in LR formation in the slr-1 mutant, but not in the slr-1 arf7 arf19 triple mutant, suggesting that normal HDAC activity is required for the mIAA14-mediated inactivation of ARF7/19 functions in LR initiation. Taken together, our data suggest that PKL/SSL2-mediated chromatin remodeling negatively regulates auxin-mediated LR formation in Arabidopsis.
authors.affiliation: Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, 630-0101 Ikoma, Nara, Japan. h-fukaki@port.kobe-u.ac.jp
authors.forename: Hidehiro
authors.initials: H
authors.lastname: Fukaki
authors.forename: Naohide
authors.initials: N
authors.lastname: Taniguchi
authors.forename: Masao
authors.initials: M
authors.lastname: Tasaka
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development*; D029681:Arabidopsis Proteins / Q000502:physiology*; D001483:Base Sequence; D004265:DNA Helicases; D017931:DNA Primers; D005816:Genetic Complementation Test; D006655:Histone Deacetylases / Q000378:metabolism; D009154:Mutation; D018517:Plant Roots / Q000254:growth & development*; D015534:Trans-Activators / Q000502:physiology*; D014157:Transcription Factors / Q000502:physiology*
chemical_list: C503426:ARF19 protein, Arabidopsis; C503425:ARF7 protein, Arabidopsis; D029681:Arabidopsis Proteins; D017931:DNA Primers; C507566:IAA14 protein, Arabidopsis; D015534:Trans-Activators; D014157:Transcription Factors; D006655:Histone Deacetylases; C402442:AT2G25170 protein, Arabidopsis; D004265:DNA Helicases