title: Sad3 and sad4 are required for saponin biosynthesis and root development in oat.
abstract: Avenacins are antimicrobial triterpene glycosides that are produced by oat (Avena) roots. These compounds confer broad-spectrum resistance to soil pathogens. Avenacin A-1, the major avenacin produced by oats, is strongly UV fluorescent and accumulates in root epidermal cells. We previously defined nine loci required for avenacin synthesis, eight of which are clustered. Mutants affected at seven of these (including Saponin-deficient1 [Sad1], the gene for the first committed enzyme in the pathway) have normal root morphology but reduced root fluorescence. In this study, we focus on mutations at the other two loci, Sad3 (also within the gene cluster) and Sad4 (unlinked), which result in stunted root growth, membrane trafficking defects in the root epidermis, and root hair deficiency. While sad3 and sad4 mutants both accumulate the same intermediate, monodeglucosyl avenacin A-1, the effect on avenacin A-1 glucosylation in sad4 mutants is only partial. sad1/sad1 sad3/sad3 and sad1/sad1 sad4/sad4 double mutants have normal root morphology, implying that the accumulation of incompletely glucosylated avenacin A-1 disrupts membrane trafficking and causes degeneration of the epidermis, with consequential effects on root hair formation. Various lines of evidence indicate that these effects are dosage-dependent. The significance of these data for the evolution and maintenance of the avenacin gene cluster is discussed.
authors.affiliation: John Ines Centre, Norwich NR4 7UH, United Kingdom.
authors.forename: Panagiota
authors.initials: P
authors.lastname: Mylona
authors.forename: Amorn
authors.initials: A
authors.lastname: Owatworakit
authors.forename: Kalliopi
authors.initials: K
authors.lastname: Papadopoulou
authors.forename: Helen
authors.initials: H
authors.lastname: Jenner
authors.forename: Bo
authors.initials: B
authors.lastname: Qin
authors.forename: Kim
authors.initials: K
authors.lastname: Findlay
authors.forename: Lionel
authors.initials: L
authors.lastname: Hill
authors.forename: Xiaoquan
authors.initials: X
authors.lastname: Qi
authors.forename: Saleha
authors.initials: S
authors.lastname: Bakht
authors.forename: Rachel
authors.initials: R
authors.lastname: Melton
authors.forename: Anne
authors.initials: A
authors.lastname: Osbourn
mesh_terms: D000483:Alleles; D018554:Avena / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D005453:Fluorescence; D018628:Gene Dosage; D046529:Microscopy, Electron, Transmission; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D019441:Plant Epidermis / Q000166:cytology / Q000378:metabolism / Q000648:ultrastructure; D010940:Plant Proteins / Q000378:metabolism*; D018517:Plant Roots / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D012503:Saponins / Q000096:biosynthesis* / Q000737:chemistry / Q000378:metabolism; D013261:Sterols / Q000737:chemistry / Q000378:metabolism
chemical_list: D010940:Plant Proteins; D012503:Saponins; D013261:Sterols; C091460:avenacin A 1