title: The CKI1 Histidine Kinase Specifies the Female Gametic Precursor of the Endosperm.
abstract: Since the discovery of double fertilization, it has been recognized that flowering plants produce two highly dimorphic female gametes, the egg cell and central cell. These give rise, respectively, to the embryo and the endosperm, a nourishing tissue unique to flowering plants. Here we show that in Arabidopsis, endosperm formation requires the CYTOKININ INDEPENDENT 1 (CKI1) histidine kinase, an activator of the cytokinin signaling pathway, which specifies central cells and restricts egg cell fate. Dimorphism of the two adjacent gametes is mechanistically established in the syncytial embryo sac by spatially restricted CKI1 expression, followed by translocation of ER-localized CKI1 protein via nuclear migration. Cell specification by CKI1 likely involves activation of the cytokinin signaling pathway mediated by histidine phosphotransferases. Ectopic CKI1 expression generates non-propagating seeds with dual fertilized endosperms and no embryos. We conclude that CKI1-directed specification of the endosperm precursor central cell results in seeds containing an embryo and an endosperm.
authors.affiliation: Department of Plant Biology, University of California, Davis, CA 95616, USA.
authors.forename: Li
authors.initials: L
authors.lastname: Yuan
authors.affiliation: Department of Plant Biology, University of California, Davis, CA 95616, USA; Laboratory of Cell and Molecular Biology, Institute of Vegetable Science, Zhejiang University, Hangzhou 310058, China; Laboratory of Horticultural Plant Growth and Quality Regulation, Ministry of Agriculture, Hangzhou 310058, China.
authors.forename: Zhenning
authors.initials: Z
authors.lastname: Liu
authors.affiliation: Department of Plant Biology, University of California, Davis, CA 95616, USA.
authors.forename: Xiaoya
authors.initials: X
authors.lastname: Song
authors.affiliation: Department of Plant Biology, University of California, Davis, CA 95616, USA.
authors.forename: Cameron
authors.initials: C
authors.lastname: Johnson
authors.affiliation: Laboratory of Cell and Molecular Biology, Institute of Vegetable Science, Zhejiang University, Hangzhou 310058, China; Laboratory of Horticultural Plant Growth and Quality Regulation, Ministry of Agriculture, Hangzhou 310058, China.
authors.forename: Xiaolin
authors.initials: X
authors.lastname: Yu
authors.affiliation: Department of Plant Biology, University of California, Davis, CA 95616, USA; Department of Plant Sciences, University of California, Davis, CA 95616, USA. Electronic address: sundar@ucdavis.edu.
authors.forename: Venkatesan
authors.initials: V
authors.lastname: Sundaresan
mesh_terms: D017360:Arabidopsis / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000235:genetics*; D003583:Cytokinins / Q000235:genetics; D004721:Endoplasmic Reticulum / Q000378:metabolism; D056625:Endosperm / Q000166:cytology* / Q000235:genetics; D005306:Fertilization / Q000502:physiology; D055993:Germ Cells, Plant / Q000166:cytology*; D049452:Green Fluorescent Proteins / Q000235:genetics; D010770:Phosphotransferases / Q000378:metabolism; D030821:Plants, Genetically Modified; D011494:Protein Kinases / Q000235:genetics*; D012639:Seeds / Q000196:embryology*; D015398:Signal Transduction / Q000235:genetics
chemical_list: D029681:Arabidopsis Proteins; D003583:Cytokinins; D049452:Green Fluorescent Proteins; D010770:Phosphotransferases; D011494:Protein Kinases; C101990:CKI1 protein, Arabidopsis