title: E151 (sym15), a pleiotropic mutant of pea (Pisum sativum L.), displays low nodule number, enhanced mycorrhizae, delayed lateral root emergence, and high root cytokinin levels.
abstract: In legumes, the formation of rhizobial and mycorrhizal root symbioses is a highly regulated process which requires close communication between plant and microorganism. Plant mutants that have difficulties establishing symbioses are valuable tools for unravelling the mechanisms by which these symbioses are formed and regulated. Here E151, a mutant of Pisum sativum cv. Sparkle, was examined to characterize its root growth and symbiotic defects. The symbioses in terms of colonization intensity, functionality of micro-symbionts, and organ dominance were compared between the mutant and wild type. The endogenous cytokinin (CK) and abscisic acid (ABA) levels and the effect of the exogenous application of these two hormones were determined. E151 was found to be a low and delayed nodulator, exhibiting defects in both the epidermal and cortical programmes though a few mature and functional nodules develop. Mycorrhizal colonization of E151 was intensified, although the fungal functionality was impaired. Furthermore, E151 displayed an altered lateral root (LR) phenotype compared with that of the wild type whereby LR emergence is initially delayed but eventually overcome. No differences in ABA levels were found between the mutant and the wild type, but non-inoculated E151 exhibited significantly high CK levels. It is hypothesized that CK plays an essential role in differentially mediating the entry of the two micro-symbionts into the cortex; whereas it would inhibit the entry of the rhizobia in that tissue, it would promote that of the fungus. E151 is a developmental mutant which may prove to be a useful tool in further understanding the role of hormones in the regulation of beneficial root symbioses.
authors.affiliation: Biology Department, 75 University Avenue W, Wilfrid Laurier University, Waterloo, ON, Canada, N2L 3C5.
authors.forename: James M C
authors.initials: JM
authors.lastname: Jones
authors.affiliation: Biology Department, 75 University Avenue W, Wilfrid Laurier University, Waterloo, ON, Canada, N2L 3C5.
authors.forename: Lindsey
authors.initials: L
authors.lastname: Clairmont
authors.affiliation: Biology Department, 75 University Avenue W, Wilfrid Laurier University, Waterloo, ON, Canada, N2L 3C5.
authors.forename: Emily S
authors.initials: ES
authors.lastname: Macdonald
authors.affiliation: Biology Department, 75 University Avenue W, Wilfrid Laurier University, Waterloo, ON, Canada, N2L 3C5.
authors.forename: Catherine A
authors.initials: CA
authors.lastname: Weiner
authors.affiliation: Biology Department, 1600 West Bank Drive, Trent University, Peterborough, ON, Canada, K9J 7B8.
authors.forename: R J Neil
authors.initials: RJ
authors.lastname: Emery
authors.affiliation: Biology Department, 75 University Avenue W, Wilfrid Laurier University, Waterloo, ON, Canada, N2L 3C5 fguinel@wlu.ca.
authors.forename: Frédérique C
authors.initials: FC
authors.lastname: Guinel
mesh_terms: D000040:Abscisic Acid / Q000494:pharmacology; D064751:Ammonium Compounds / Q000494:pharmacology; D003583:Cytokinins / Q000378:metabolism*; D058685:Genetic Pleiotropy; D009154:Mutation / Q000235:genetics*; D038821:Mycorrhizae / Q000187:drug effects / Q000254:growth & development / Q000502:physiology*; D009566:Nitrates / Q000494:pharmacology; D018532:Pisum sativum / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism* / Q000382:microbiology*; D010641:Phenotype; D019441:Plant Epidermis / Q000187:drug effects / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D055170:Plant Root Nodulation / Q000187:drug effects; D053204:Root Nodules, Plant / Q000187:drug effects / Q000378:metabolism*; D036226:Seedlings / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism
chemical_list: D064751:Ammonium Compounds; D003583:Cytokinins; D009566:Nitrates; D010940:Plant Proteins; D000040:Abscisic Acid
keywords: Abscisic acid; cytokinin; epidermal–cortex interface; infection thread; legume; mycorrhiza formation; nodulation; pea mutant; root development.