title: The half-size ABC transporters STR1 and STR2 are indispensable for mycorrhizal arbuscule formation in rice.
abstract: The central structure of the symbiotic association between plants and arbuscular mycorrhizal (AM) fungi is the fungal arbuscule that delivers minerals to the plant. Our earlier transcriptome analyses identified two half-size ABCG transporters that displayed enhanced mRNA levels in mycorrhizal roots. We now show specific transcript accumulation in arbusculated cells of both genes during symbiosis. Presently, arbuscule-relevant factors from monocotyledons have not been reported. Mutation of either of the Oryza sativa (rice) ABCG transporters blocked arbuscule growth of different AM fungi at a small and stunted stage, recapitulating the phenotype of Medicago truncatula stunted arbuscule 1 and 2 (str1 and str2) mutants that are deficient in homologous ABCG genes. This phenotypic resemblance and phylogenetic analysis suggest functional conservation of STR1 and STR2 across the angiosperms. Malnutrition of the fungus underlying limited arbuscular growth was excluded by the absence of complementation of the str1 phenotype by wild-type nurse plants. Furthermore, plant AM signaling was found to be intact, as arbuscule-induced marker transcript accumulation was not affected in str1 mutants. Strigolactones have previously been hypothesized to operate as intracellular hyphal branching signals and possible substrates of STR1 and STR2. However, full arbuscule development in the strigolactone biosynthesis mutants d10 and d17 suggested strigolactones to be unlikely substrates of STR1/STR2. Interestingly, rice STR1 is associated with a cis-natural antisense transcript (antiSTR1). Analogous to STR1 and STR2, at the root cortex level, the antiSTR1 transcript is specifically detected in arbusculated cells, suggesting unexpected modes of STR1 regulation in rice.
authors.affiliation: Department of Plant Molecular Biology, University of Lausanne, Switzerland.
authors.forename: Caroline
authors.initials: C
authors.lastname: Gutjahr
authors.forename: Dragica
authors.initials: D
authors.lastname: Radovanovic
authors.forename: Jessika
authors.initials: J
authors.lastname: Geoffroy
authors.forename: Quan
authors.initials: Q
authors.lastname: Zhang
authors.forename: Heike
authors.initials: H
authors.lastname: Siegler
authors.forename: Marco
authors.initials: M
authors.lastname: Chiapello
authors.forename: Leonardo
authors.initials: L
authors.lastname: Casieri
authors.forename: Kyungsook
authors.initials: K
authors.lastname: An
authors.forename: Gynheung
authors.initials: G
authors.lastname: An
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Guiderdoni
authors.forename: Chellian Santhosh
authors.initials: CS
authors.lastname: Kumar
authors.forename: Venkatesan
authors.initials: V
authors.lastname: Sundaresan
authors.forename: Maria J
authors.initials: MJ
authors.lastname: Harrison
authors.forename: Uta
authors.initials: U
authors.lastname: Paszkowski
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D007783:Lactones / Q000378:metabolism; D009154:Mutation; D038821:Mycorrhizae / Q000502:physiology*; D012275:Oryza / Q000235:genetics* / Q000378:metabolism / Q000382:microbiology; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000235:genetics / Q000378:metabolism / Q000382:microbiology; D013559:Symbiosis / Q000235:genetics*
chemical_list: D018528:ATP-Binding Cassette Transporters; D007783:Lactones; D010940:Plant Proteins