title: Embryo defective 14 encodes a plastid-targeted cGTPase essential for embryogenesis in maize.
abstract: The embryo defective (emb) mutants in maize genetically define a unique class of loci that is required for embryogenesis but not endosperm development, allowing dissection of two developmental processes of seed formation. Through characterization of the emb14 mutant, we report here that Emb14 gene encodes a circular permuted, YqeH class GTPase protein that likely functions in 30S ribosome formation in plastids. Loss of Emb14 function in the null mutant arrests embryogenesis at the early transition stage. Emb14 was cloned by transposon tagging and was confirmed by analysis of four alleles. Subcellular localization indicated that the EMB14 is targeted to chloroplasts. Recombinant EMB14 is shown to hydrolyze GTP in vitro (Km  = 2.42 ± 0.3 μm). Emb14 was constitutively expressed in all tissues examined and high level of expression was found in transition stage embryos. Comparison of emb14 and WT indicated that loss of EMB14 function severely impairs accumulation of 16S rRNA and several plastid encoded ribosomal genes. We show that an EMB14 transgene complements the pale green, slow growth phenotype conditioned by mutations in AtNOA1, a closely related YqeH GTPase of Arabidopsis. Taken together, we propose that the EMB14/AtNOA1/YqeH class GTPases function in assembly of the 30S subunit of the chloroplast ribosome, and that this function is essential to embryogenesis in plants.
authors.affiliation: Key Laboratory of Plant Cell Engineering and Germplasm Innovation, Ministry of Education, School of Life Sciences, Shandong University, Jinan, Shandong, 250100, China.
authors.forename: Cuiling
authors.initials: C
authors.lastname: Li
authors.affiliation: State Key Lab of Agrobiotechnology, Institute of Plant Molecular Biology and Agrobiotechnology, School of Life Science, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China.
authors.forename: Yun
authors.initials: Y
authors.lastname: Shen
authors.affiliation: DuPont Pioneer AgBiotech Research, Johnston, Iowa, 50131-1004, USA.
authors.forename: Robert
authors.initials: R
authors.lastname: Meeley
authors.affiliation: Horticultural Sciences Department, University of Florida, Gainesville, FL, 32611, USA.
authors.forename: Donald R
authors.initials: DR
authors.lastname: McCarty
authors.affiliation: Key Laboratory of Plant Cell Engineering and Germplasm Innovation, Ministry of Education, School of Life Sciences, Shandong University, Jinan, Shandong, 250100, China.|State Key Lab of Agrobiotechnology, Institute of Plant Molecular Biology and Agrobiotechnology, School of Life Science, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China.
authors.forename: Bao-Cai
authors.initials: BC
authors.lastname: Tan
mesh_terms: D000595:Amino Acid Sequence; D060365:Chloroplast Proteins / Q000235:genetics / Q000378:metabolism; D020558:GTP Phosphohydrolases / Q000235:genetics / Q000378:metabolism*; D020869:Gene Expression Profiling / Q000379:methods; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D006160:Guanosine Triphosphate / Q000378:metabolism; D015151:Immunoblotting; D017403:In Situ Hybridization; D007700:Kinetics; D008969:Molecular Sequence Data; D009154:Mutation; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D018087:Plastids / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012639:Seeds / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D003313:Zea mays / Q000254:growth & development / Q000378:metabolism*
chemical_list: D060365:Chloroplast Proteins; D010940:Plant Proteins; D006160:Guanosine Triphosphate; D020558:GTP Phosphohydrolases
keywords: cGTPase; embryogenesis; maize; plastids; ribosome