The glaucous appearance of wheat (Triticum aestivum) and barley (Hordeum vulgare) plants, that is the light bluish-gray look of flag leaf, stem, and spike surfaces, results from deposition of cuticular β-diketone wax on their surfaces; this phenotype is associated with high yield, especially under drought conditions. Despite extensive genetic and biochemical characterization, the molecular genetic basis underlying the biosynthesis of β-diketones remains unclear. Here, we discovered that the wheat W1 locus contains a metabolic gene cluster mediating β-diketone biosynthesis. The cluster comprises genes encoding proteins of several families including type-III polyketide synthases, hydrolases, and cytochrome P450s related to known fatty acid hydroxylases. The cluster region was identified in both genetic and physical maps of glaucous and glossy tetraploid wheat, demonstrating entirely different haplotypes in these accessions. Complementary evidence obtained through gene silencing in planta and heterologous expression in bacteria supports a model for a β-diketone biosynthesis pathway involving members of these three protein families. Mutations in homologous genes were identified in the barley eceriferum mutants defective in β-diketone biosynthesis, demonstrating a gene cluster also in the β-diketone biosynthesis Cer-cqu locus in barley. Hence, our findings open new opportunities to breed major cereal crops for surface features that impact yield and stress response.
Bibliographical noteFunding Information:
We thank Moshe Feldman for kindly providing the wheat lines BL and CASL2BS used in the study. We thank Rebecca Lauder from Bioimaging at Rothamsted Research, UK, for conducting part of the electron microscopy experiments and Tamar Unger from the Structural Proteomics Unit, faculty of biochemistry at the Weizmann Institute of Science for assistance with protein expression. We thank David R. Nelson for the kind assistance with CYP nomenclature. G.F. is Incumbent of the David and Stacey Cynamon Reaserch Fellow Chair in Genetics and Personalized Medicine. This work was supported by an Israel Science Foundation (ISF) personal grant to A.A. (ISF Grant 646/11) and the European Research Council (SAMIT-FP7 program). We thank the Adelis Foundation, Leona M. and Harry B. Helmsley Charitable Trust, Jeanne and Joseph Nissim Foundation for Life Sciences, Tomand Sondra Rykoff Family Foundation Research, and the Raymond Burton Plant Genome Research Fund for supporting the A.A. lab activity. A.A. is the incumbent of the Peter J. Cohn Professorial Chair. This work was also supported by Natural Sciences and Engineering Research Council Discovery Grant 2208738 (Canada), the Canada Foundation for Innovation Grant 201681, and UK Biotechnology and Biological Sciences Research Council Grants BB/J004588/1, BB/H018824/1, and BB/J00426X/1.
© 2016 American Society of Plant Biologists.
ASJC Scopus subject areas
- Plant Science
- Cell Biology