title: Impaired auxin biosynthesis in the defective endosperm18 mutant is due to mutational loss of expression in the ZmYuc1 gene encoding endosperm-specific YUCCA1 protein in maize.
abstract: The phytohormone auxin (indole-3-acetic acid [IAA]) plays a fundamental role in vegetative and reproductive plant development. Here, we characterized a seed-specific viable maize (Zea mays) mutant, defective endosperm18 (de18) that is impaired in IAA biosynthesis. de18 endosperm showed large reductions of free IAA levels and is known to have approximately 40% less dry mass, compared with De18. Cellular analyses showed lower total cell number, smaller cell volume, and reduced level of endoreduplication in the mutant endosperm. Gene expression analyses of seed-specific tryptophan-dependent IAA pathway genes, maize Yucca1 (ZmYuc1), and two tryptophan-aminotransferase co-orthologs were performed to understand the molecular basis of the IAA deficiency in the mutant. Temporally, all three genes showed high expression coincident with high IAA levels; however, only ZmYuc1 correlated with the reduced IAA levels in the mutant throughout endosperm development. Furthermore, sequence analyses of ZmYuc1 complementary DNA and genomic clones revealed many changes specific to the mutant, including a 2-bp insertion that generated a premature stop codon and a truncated YUC1 protein of 212 amino acids, compared with the 400 amino acids in the De18. The putative, approximately 1.5-kb, Yuc1 promoter region also showed many rearrangements, including a 151-bp deletion in the mutant. Our concurrent high-density mapping and annotation studies of chromosome 10, contig 395, showed that the De18 locus was tightly linked to the gene ZmYuc1. Collectively, the data suggest that the molecular changes in the ZmYuc1 gene encoding the YUC1 protein are the causal basis of impairment in a critical step in IAA biosynthesis, essential for normal endosperm development in maize.
authors.affiliation: Institute of Agronomy, Genetics and Crop Science, Università Cattolica del Sacro Cuore, 29122 Piacenza, Italy.
authors.forename: Jamila
authors.initials: J
authors.lastname: Bernardi
authors.forename: Alessandra
authors.initials: A
authors.lastname: Lanubile
authors.forename: Qin-Bao
authors.initials: QB
authors.lastname: Li
authors.forename: Dibyendu
authors.initials: D
authors.lastname: Kumar
authors.forename: Ales
authors.initials: A
authors.lastname: Kladnik
authors.forename: Sam D
authors.initials: SD
authors.lastname: Cook
authors.forename: John J
authors.initials: JJ
authors.lastname: Ross
authors.forename: Adriano
authors.initials: A
authors.lastname: Marocco
authors.forename: Prem S
authors.initials: PS
authors.lastname: Chourey
mesh_terms: D001483:Base Sequence; D053898:Biosynthetic Pathways / Q000235:genetics; D048429:Cell Size; D003001:Cloning, Molecular; D056625:Endosperm / Q000235:genetics* / Q000254:growth & development; D004926:Escherichia coli / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant / Q000235:genetics*; D056426:Genetic Loci / Q000235:genetics; D007210:Indoleacetic Acids / Q000378:metabolism*; D009154:Mutation / Q000235:genetics*; D009928:Organ Specificity / Q000235:genetics; D020161:Physical Chromosome Mapping; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D016133:Polymerase Chain Reaction; D011110:Polymorphism, Genetic; D011123:Polyploidy; D011994:Recombinant Proteins / Q000378:metabolism; D003313:Zea mays / Q000166:cytology / Q000196:embryology* / Q000235:genetics*
chemical_list: D007210:Indoleacetic Acids; D010940:Plant Proteins; D011994:Recombinant Proteins