Abstract
Arabidopsis SIZ1 encodes a SUMO E3 ligase to regulate abiotic and biotic stress responses. Among SIZ1 or mammalian PIAS orthologs, plant SIZ1 proteins contain the plant homeodomain (PHD) finger, a C4HC3 zinc finger. Here, we investigated the importance of PHD of Arabidopsis SIZ1. The ProSIZ1::SIZ1(ΔPHD):GFP was unable to complement growth retardation, ABA hypersensitivity, and the cold-sensitive phenotype of the siz1 mutant, but ProSIZ1::SIZ1:GFP could. Substitution of C162S in the PHD finger was unable to complement the siz1 mutation. Tri-methylated histone H3K4 (H3K4me3) was recognized by PHD, not by PHD(C162S). WRKY70 was up-regulated in the siz1-2 mutant and H3K4me3 accumulated at high levels in the WRKY70 promoter. PHD interacts with ATX, which mediates methylation of histone, probably leading to suppression of ATX’s function. These results suggest that the PHD finger of SIZ1 is important for recognition of the histone code and is required for SIZ1 function and transcriptional suppression.
Highlights
Introduction ofProSIZ1::SAP and MIZ1 domain-containing ligase1 (SIZ1):GFP or ProSIZ1::SIZ1(C117S):GFP complemented the dwarf-like phenotype of siz[1,2]; introduction of ProSIZ1::SIZ1(C162S): GFP or ProSIZ1::SIZ1(ΔPHD):GFP was unable to complement the dwarf-like phenotype of siz1-2. b Expression of SIZ1 in each plant
In vitro analysis revealed that the plant homeodomain (PHD) and SP-RING domains of Arabidopsis AtSIZ1 are required for binding to the AtSCE1, the small ubiquitin-like modifier (SUMO) E2conjugating enzyme, and for sumoylation[30]
To confirm whether the PHD finger is important for SIZ1 function, ProSIZ1::SIZ1(ΔPHD):GFP was expressed in the siz[1,2] mutant to complement the dwarf-like phenotype
Summary
Introduction ofProSIZ1::SIZ1:GFP or ProSIZ1::SIZ1(C117S):GFP complemented the dwarf-like phenotype of siz[1,2]; introduction of ProSIZ1::SIZ1(C162S): GFP or ProSIZ1::SIZ1(ΔPHD):GFP was unable to complement the dwarf-like phenotype of siz1-2. b Expression of SIZ1 in each plant. ProSIZ1::SIZ1:GFP or ProSIZ1::SIZ1(C117S):GFP complemented the dwarf-like phenotype of siz[1,2]; introduction of ProSIZ1::SIZ1(C162S): GFP or ProSIZ1::SIZ1(ΔPHD):GFP was unable to complement the dwarf-like phenotype of siz. B Expression of SIZ1 in each plant. SIZ1 was not detected in the siz[1,2] mutant. SIZ1 transcripts were detected in other plants. C Amino-acid sequence and structural information of the PHD finger in SIZ1. Purple and yellow arrows indicate α-helices and β-sheets, respectively.
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