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Plant Cell Advance Online Publication
Published on October 12, 2007; 10.1105/tpc.106.048868

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Received November 12, 2006
Returned for revision September 18, 2007
Accepted September 25, 2007

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

Qing Tian 1, Lene Olsen 2, Beimeng Sun 1, Stein Erik Lid 2, Roy C. Brown 3, Betty E. Lemmon 3, Kjetil Fosnes 2, Darren (Fred) Gruis 1, Hilde-Gunn Opsahl-Sorteberg 2, Marisa S. Otegui 4, and Odd-Arne Olsen 1*

1 Pioneer Hi-Bred International, A DuPont Business, Johnston, Iowa 50131
2 Norwegian University of Life Sciences, 1432 Ås, Norway
3 University of Louisiana at Lafayette, Lafayette, Louisiana 70504-2451
4 Department of Botany, University of Wisconsin, Madison, Wisconsin 53706

* To whom correspondence should be addressed. E-mail: odd-arne.olsen{at}monsanto.com.

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.






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