title: micro RNA 172 (miR172) signals epidermal infection and is expressed in cells primed for bacterial invasion in Lotus japonicus roots and nodules.
abstract: Legumes interact with rhizobial bacteria to form nitrogen-fixing root nodules. Host signalling following mutual recognition ensures a specific response, but is only partially understood. Focusing on the stage of epidermal infection with Mesorhizobium loti, we analysed endogenous small RNAs (sRNAs) of the model legume Lotus japonicus to investigate their involvement in host response regulation. We used Illumina sequencing to annotate the L. japonicus sRNA-ome and isolate infection-responsive sRNAs, followed by candidate-based functional characterization. Sequences from four libraries revealed 219 novel L. japonicus micro RNAs (miRNAs) from 114 newly assigned families, and 76 infection-responsive sRNAs. Unlike infection-associated coding genes such as NODULE INCEPTION (NIN), a micro RNA 172 (miR172) isoform showed strong accumulation in dependency of both Nodulation (Nod) factor and compatible rhizobia. The genetics of miR172 induction support the existence of distinct epidermal and cortical signalling events. MIR172a promoter activity followed a previously unseen pattern preceding infection thread progression in epidermal and cortical cells. Nodule-associated miR172a expression was infection-independent, representing the second of two genetically separable activity waves. The combined data provide a valuable resource for further study, and identify miR172 as an sRNA marking successful epidermal infection. We show that miR172 acts upstream of several APETALA2-type (AP2) transcription factors, and suggest that it has a role in fine-tuning AP2 levels during bacterial symbiosis.
authors.affiliation: Department of Molecular Biology and Genetics, Centre for Carbohydrate Recognition and Signalling (CARB), Aarhus University, Gustav Wieds Vej 10, 8000, Aarhus C, Denmark.
authors.forename: Dennis B
authors.initials: DB
authors.lastname: Holt
authors.affiliation: Department of Molecular Biology and Genetics, Centre for Carbohydrate Recognition and Signalling (CARB), Aarhus University, Gustav Wieds Vej 10, 8000, Aarhus C, Denmark.
authors.forename: Vikas
authors.initials: V
authors.lastname: Gupta
authors.affiliation: Department of Molecular Biology and Genetics, Centre for Carbohydrate Recognition and Signalling (CARB), Aarhus University, Gustav Wieds Vej 10, 8000, Aarhus C, Denmark.
authors.forename: Dörte
authors.initials: D
authors.lastname: Meyer
authors.affiliation: Department of Molecular Biology and Genetics, Centre for Carbohydrate Recognition and Signalling (CARB), Aarhus University, Gustav Wieds Vej 10, 8000, Aarhus C, Denmark.
authors.forename: Nikolaj B
authors.initials: NB
authors.lastname: Abel
authors.affiliation: Department of Molecular Biology and Genetics, Centre for Carbohydrate Recognition and Signalling (CARB), Aarhus University, Gustav Wieds Vej 10, 8000, Aarhus C, Denmark.
authors.forename: Stig U
authors.initials: SU
authors.lastname: Andersen
authors.affiliation: Department of Molecular Biology and Genetics, Centre for Carbohydrate Recognition and Signalling (CARB), Aarhus University, Gustav Wieds Vej 10, 8000, Aarhus C, Denmark.
authors.forename: Jens
authors.initials: J
authors.lastname: Stougaard
authors.affiliation: Department of Molecular Biology and Genetics, Centre for Carbohydrate Recognition and Signalling (CARB), Aarhus University, Gustav Wieds Vej 10, 8000, Aarhus C, Denmark.
authors.forename: Katharina
authors.initials: K
authors.lastname: Markmann
mesh_terms: D060026:Endophytes / Q000254:growth & development; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D000070116:Lotus / Q000235:genetics* / Q000378:metabolism / Q000382:microbiology; D059128:Mesorhizobium / Q000254:growth & development*; D035683:MicroRNAs / Q000378:metabolism*; D010641:Phenotype; D019441:Plant Epidermis / Q000378:metabolism / Q000382:microbiology*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism / Q000382:microbiology; D011401:Promoter Regions, Genetic; D012231:Rhizobium; D053204:Root Nodules, Plant / Q000382:microbiology*; D015398:Signal Transduction; D013559:Symbiosis; D014157:Transcription Factors / Q000378:metabolism
chemical_list: D035683:MicroRNAs; D010940:Plant Proteins; D014157:Transcription Factors
keywords: Lotus japonicus; epidermal infection; micro RNA 172 (miR172); micro RNAs in symbiosis; nodulation symbiosis; small RNA sequencing