title: Subcellular localization and functional domain studies of DEFECTIVE KERNEL1 in maize and Arabidopsis suggest a model for aleurone cell fate specification involving CRINKLY4 and SUPERNUMERARY ALEURONE LAYER1.
abstract: DEFECTIVE KERNEL1 (DEK1), which consists of a membrane-spanning region (DEK1-MEM) and a calpain-like Cys proteinase region (DEK1-CALP), is essential for aleurone cell formation at the surface of maize (Zea mays) endosperm. Immunolocalization and FM4-64 dye incubation experiments showed that DEK1 and CRINKLY4 (CR4), a receptor kinase implicated in aleurone cell fate specification, colocalized to plasma membrane and endosomes. SUPERNUMERARY ALEURONE LAYER1 (SAL1), a negative regulator of aleurone cell fate encoding a class E vacuolar sorting protein, colocalized with DEK1 and CR4 in endosomes. Immunogold localization, dual-axis electron tomography, and diffusion of fluorescent dye tracers showed that young aleurone cells established symplastic subdomains through plasmodesmata of larger dimensions than those connecting starchy endosperm cells and that CR4 preferentially associated with plasmodesmata between aleurone cells. Genetic complementation experiments showed that DEK1-CALP failed to restore wild-type phenotypes in maize and Arabidopsis thaliana dek1 mutants, and DEK1-MEM also failed to restore wild-type phenotypes in Arabidopsis dek1-1 mutants. Instead, ectopic expression of DEK1-MEM under the control of the cauliflower mosaic virus 35S promoter gave a dominant negative phenotype. These data suggest a model for aleurone cell fate specification in which DEK1 perceives and/or transmits a positional signal, CR4 promotes the lateral movement of aleurone signaling molecules between aleurone cells, and SAL1 maintains the proper plasma membrane concentration of DEK1 and CR4 proteins via endosome-mediated recycling/degradation.
authors.affiliation: Pioneer Hi-Bred International, A DuPont Business, Johnston, Iowa 50131, USA.
authors.forename: Qing
authors.initials: Q
authors.lastname: Tian
authors.forename: Lene
authors.initials: L
authors.lastname: Olsen
authors.forename: Beimeng
authors.initials: B
authors.lastname: Sun
authors.forename: Stein Erik
authors.initials: SE
authors.lastname: Lid
authors.forename: Roy C
authors.initials: RC
authors.lastname: Brown
authors.forename: Betty E
authors.initials: BE
authors.lastname: Lemmon
authors.forename: Kjetil
authors.initials: K
authors.lastname: Fosnes
authors.forename: Darren Fred
authors.initials: DF
authors.lastname: Gruis
authors.forename: Hilde-Gunn
authors.initials: HG
authors.lastname: Opsahl-Sorteberg
authors.forename: Marisa S
authors.initials: MS
authors.lastname: Otegui
authors.forename: Odd-Arne
authors.initials: OA
authors.lastname: Olsen
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002154:Calpain / Q000235:genetics / Q000378:metabolism*; D002454:Cell Differentiation / Q000235:genetics / Q000502:physiology; D002462:Cell Membrane / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D015151:Immunoblotting; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D008954:Models, Biological; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D003313:Zea mays / Q000235:genetics / Q000254:growth & development / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D029681:Arabidopsis Proteins; D010940:Plant Proteins; D011494:Protein Kinases; D002154:Calpain; C507125:DEK1 protein, Arabidopsis