title: Loss of abaxial leaf epicuticular wax in Medicago truncatula irg1/palm1 mutants results in reduced spore differentiation of anthracnose and nonhost rust pathogens.
abstract: To identify genes that confer nonhost resistance to biotrophic fungal pathogens, we did a forward-genetics screen using Medicago truncatula Tnt1 retrotransposon insertion lines. From this screen, we identified an inhibitor of rust germ tube differentation1 (irg1) mutant that failed to promote preinfection structure differentiation of two rust pathogens, Phakopsora pachyrhizi and Puccinia emaculata, and one anthracnose pathogen, Colletotrichum trifolii, on the abaxial leaf surface. Cytological and chemical analyses revealed that the inhibition of rust preinfection structures in irg1 mutants is due to complete loss of the abaxial epicuticular wax crystals and reduced surface hydrophobicity. The composition of waxes on abaxial leaf surface of irg1 mutants had >90% reduction of C30 primary alcohols and a preferential increase of C29 and C31 alkanes compared with the wild type. IRG1 encodes a Cys(2)His(2) zinc finger transcription factor, PALM1, which also controls dissected leaf morphology in M. truncatula. Transcriptome analysis of irg1/palm1 mutants revealed downregulation of eceriferum4, an enzyme implicated in primary alcohol biosynthesis, and MYB96, a major transcription factor that regulates wax biosynthesis. Our results demonstrate that PALM1 plays a role in regulating epicuticular wax metabolism and transport and that epicuticular wax influences spore differentiation of host and nonhost fungal pathogens.
authors.affiliation: Plant Biology Division, The Samuel Roberts Noble Foundation, Ardmore, Oklahoma 73401, USA.
authors.forename: Srinivasa Rao
authors.initials: SR
authors.lastname: Uppalapati
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Ishiga
authors.forename: Vanthana
authors.initials: V
authors.lastname: Doraiswamy
authors.forename: Mohamed
authors.initials: M
authors.lastname: Bedair
authors.forename: Shipra
authors.initials: S
authors.lastname: Mittal
authors.forename: Jianghua
authors.initials: J
authors.lastname: Chen
authors.forename: Jin
authors.initials: J
authors.lastname: Nakashima
authors.forename: Yuhong
authors.initials: Y
authors.lastname: Tang
authors.forename: Million
authors.initials: M
authors.lastname: Tadege
authors.forename: Pascal
authors.initials: P
authors.lastname: Ratet
authors.forename: Rujin
authors.initials: R
authors.lastname: Chen
authors.forename: Holger
authors.initials: H
authors.lastname: Schultheiss
authors.forename: Kirankumar S
authors.initials: KS
authors.lastname: Mysore
mesh_terms: D001487:Basidiomycota / Q000472:pathogenicity; D020231:Colletotrichum / Q000472:pathogenicity; D046913:Medicago truncatula / Q000235:genetics / Q000378:metabolism* / Q000382:microbiology*; D008969:Molecular Sequence Data; D010935:Plant Diseases / Q000382:microbiology; D018515:Plant Leaves / Q000378:metabolism* / Q000382:microbiology*; D010940:Plant Proteins / Q000235:genetics*; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism / Q000382:microbiology; D014885:Waxes / Q000378:metabolism*
chemical_list: D010940:Plant Proteins; D014885:Waxes