title: YAO is a nucleolar WD40-repeat protein critical for embryogenesis and gametogenesis in Arabidopsis.
abstract: BACKGROUND
  In flowering plants, gametogenesis generates multicellular male and female gametophytes. In the model system Arabidopsis, the male gametophyte or pollen grain contains two sperm cells and a vegetative cell. The female gametophyte or embryo sac contains seven cells, namely one egg, two synergids, one central cell and three antipodal cells. Double fertilization of the central cell and egg produces respectively a triploid endosperm and a diploid zygote that develops further into an embryo. The genetic control of the early embryo patterning, especially the initiation of the first zygotic division and the positioning of the cell plate, is largely unknown.
  
  
  RESULTS
  Here we report the characterization of a mutation, yaozhe (yao), that causes zygote arrest and misplacement of cell plate of the zygote, leading to early embryo lethality. In addition, gametophyte development is partially impaired. A small portion of the mutant embryo sacs are arrested at four-nucleate stage with aberrant nuclear positioning. Furthermore, the competence of male gametophytes is also compromised. YAO encodes a nucleolar protein with seven WD-repeats. Its homologues in human and yeast have been shown to be components of the U3 snoRNP complex and function in 18S rRNA processing. YAO is expressed ubiquitously, with high level of expression in tissues under active cell divisions, including embryo sacs, pollen, embryos, endosperms and root tips.
  
  
  CONCLUSIONS
  Phenotypic analysis indicated that YAO is required for the correct positioning of the first zygotic division plane and plays a critical role in gametogenesis in Arabidopsis. Since YAO is a nucleolar protein and its counterparts in yeast and human are components of the U3 snoRNP complex, we therefore postulate that YAO is most likely involved in rRNA processing in plants as well.
authors.affiliation: Key Laboratory of Molecular and Developmental Biology, Institute of Genetics and Developmental Biology, the Chinese Academy of Sciences, Beijing 100101, China.
authors.forename: Hong-Ju
authors.initials: HJ
authors.lastname: Li
authors.forename: Nai-You
authors.initials: NY
authors.lastname: Liu
authors.forename: Dong-Qiao
authors.initials: DQ
authors.lastname: Shi
authors.forename: Jie
authors.initials: J
authors.lastname: Liu
authors.forename: Wei-Cai
authors.initials: WC
authors.lastname: Yang
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism*; D002455:Cell Division / Q000235:genetics; D047108:Embryonic Development / Q000235:genetics*; D056625:Endosperm / Q000378:metabolism; D005718:Gametogenesis / Q000235:genetics*; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D019684:Magnoliopsida / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism*; D010641:Phenotype; D011058:Pollen / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment
chemical_list: D029681:Arabidopsis Proteins; D009687:Nuclear Proteins; C552507:YAO protein, Arabidopsis