Arabidopsis WD REPEAT DOMAIN55 Interacts with DNA DAMAGED BINDING PROTEIN1 and Is Required for Apical Patterning in the Embryo

Abstract

CUL4-RING ubiquitin E3 ligases (CRL4s) were recently shown to exert their specificity through the binding of various substrate receptors, which bind the CUL4 interactor DNA DAMAGED BINDING PROTEIN1 (DDB1) through a WDxR motif. In a segregation-based mutagenesis screen, we identified a WDxR motif-containing protein (WDR55) required for male and female gametogenesis and seed development. We demonstrate that WDR55 physically interacts with Arabidopsis thaliana DDB1A in planta, suggesting that WDR55 may be a novel substrate recruiter of CRL4 complexes. Examination of mutants revealed a failure in the fusion of the polar cells in embryo sac development, in addition to embryo and endosperm developmental arrest at various stages ranging from the zygote stage to the globular stage. wdr55-2 embryos suggest a defect in the transition to bilateral symmetry in the apical embryo domain, further supported by aberrant apical embryo localization of DORNROESCHEN, a direct target of the auxin response factor protein MONOPTEROS. Moreover, the auxin response pattern, as determined using the synthetic auxin-responsive reporter ProDR5:GREEN FLUORESCENT PROTEIN, was shifted in the basal embryo and suspensor but does not support a strong direct link to auxin response. Interestingly, the observed embryo and endosperm phenotype is reminiscent of CUL4 or DDB1A/B loss of function and thus may support a regulatory role of a putative CRL4 WDR55 E3 ligase complex.

TheArabidopsisDDB1 interacting protein WDR55 is required for vegetative development

“…1J). The asymmetric and radially developing seedlings may be seen in connection with a failure of establishing embryo bilateral symmetry, as observed earlier 10 . The cotyledon formation defects observed resemble auxin response mutants, such as mp (MONOPTEROS) 21 .…”

“…Proteins with these motifs, which interact with CUL4-DDB1 based E3 ligases, are referred to as DCAF (DDB1-CUL4 ASSOCIATED FACTOR) proteins, 11 and potentially target proteins for ubiquitination after they assemble with DDB1 12 , 13 . WDR55 interacts with DDB1A, suggesting that a putative CUL4-DDB1 WDR55 E3 complex regulates embryo or endosperm development 10 . The Arabidopsis CRL4s are associated with many processes such as cell cycle, DNA repair, photomorphogenesis and modulation of chromatin 14 .…”

Functional Analysis of Sporophytic Transcripts Repressed by the Female Gametophyte in the Ovule of Arabidopsis thaliana

“…Several WD40 genes that include WD repeat 55 (WD55), LACHESIS (LIS), SLOW WALKER1 (SWA1), MULTICOPY SUPRESSOR OF IRA1 ( MSI1 ), ANAPHASE-PROMOTING COMPLEX4 (APC4) , YAO , and NOF1 are known to be involved in female gametophyte development and sexual reproduction. Mutations in WD55 cause failure in the fusion of the polar nuclei and arrest of both embryo and endosperm development [56], SWA1 is expressed in cells undergoing active division and encodes a protein with six WD40 repeats that is localized in the nucleolus; mutations in SWA1 result in female gametophyte arrest at variable stages [57]. YAO encodes a nucleolar WD40-repeat component of the U3 small nucleolar RNP complex that is critical for gametogenesis and embryogenesis [58].…”

The rice DUF1620‐containing and WD40‐like repeat protein is required for the assembly of the restoration of fertility complex

“…In Arabidopsis, the WD40 domaincontaining protein WDR55 interacts with DDB1 and this interaction is required for apical patterning in the embryo. The WDR55-DDB1 complex is involved in the establishment of bilateral symmetry in the Arabidopsis embryo and may support the first link to CRL4-mediated regulation of this process (Bjerkan et al, 2012). The interactions among three subunits, RF5 (RFC1), GRP162 (RFC2) and RFC3, were dissected in this study.…”

“…WD40 repeat-containing and WD40-like repeat proteins do not possess enzymatic activity but facilitate protein-protein interactions and function as scaffold proteins for the formation of multiprotein complexes (Smith et al, 1999;Hudson & Cooley, 2008;Stirnimann et al, 2010;Bjerkan et al, 2012;Gachomo et al, 2014). The human WD40-repeat protein Han11 has four WD repeats; these WD repeats are required for coupling of MEKK1 to DYRK1 and HIPK2.…”