title: Microscopic and transcriptome analyses of early colonization of tomato roots by Trichoderma harzianum.
abstract: The capacity of the fungus Trichoderma harzianum CECT 2413 to colonize roots and stimulate plant growth was analyzed. Tobacco seedlings (Nicotiana benthamiana) transferred to Petri dishes inoculated with T. harzianum conidia showed increased plant fresh weight (140%) and foliar area (300%), as well as the proliferation of secondary roots (300%) and true leaves (140%). The interaction between strain CECT 2413 and the tomato-root system was also studied during the early stages of root colonization by the fungus. When T. harzianum conidia were inoculated into the liquid medium of hydroponically grown tomato plants (Lycopersicum esculentum), profuse adhesion of hyphae to the plant roots as well as colonization of the root epidermis and cortex were observed. Confocal microscopy of a T. harzianum transformant that expressed the green fluorescent protein (GFP) revealed intercellular hyphal growth and the formation of plant-induced papilla-like hyphal tips. Analysis of the T. harzianum-tomato interaction in soil indicated that the contact between T. harzianum and the roots persisted over a long period of time. This interaction was characterized by the presence of yeast-like cells, a novel and previously undescribed developmental change. To study the molecular mechanism underlying fungal ability to colonize the tomato-root system, the T. harzianum transcriptome was analyzed during the early stages of the plant-fungus interaction. The expression of fungal genes related to redox reactions, lipid metabolism, detoxification, and sugar or amino-acid transport increased when T. harzianum colonized tomato roots. These observations are similar to those regarding the interactions of mycorrhiza and pathogenic fungi with plants.
authors.affiliation: Institute of Plant Biochemistry and Photosynthesis, Research Center Isla de la Cartuja, CSIC, University of Sevilla, Spain.
authors.forename: Mariola R
authors.initials: MR
authors.lastname: Chacón
authors.forename: Olga
authors.initials: O
authors.lastname: Rodríguez-Galán
authors.forename: Tahía
authors.initials: T
authors.lastname: Benítez
authors.forename: Sonia
authors.initials: S
authors.lastname: Sousa
authors.forename: Manuel
authors.initials: M
authors.lastname: Rey
authors.forename: Antonio
authors.initials: A
authors.lastname: Llobell
authors.forename: Jesús
authors.initials: J
authors.lastname: Delgado-Jarana
mesh_terms: D020869:Gene Expression Profiling; D007091:Image Processing, Computer-Assisted; D018551:Solanum lycopersicum / Q000254:growth & development* / Q000382:microbiology*; D018613:Microscopy, Confocal; D020411:Oligonucleotide Array Sequence Analysis; D018517:Plant Roots / Q000254:growth & development / Q000382:microbiology; D013559:Symbiosis; D014026:Nicotiana / Q000254:growth & development / Q000382:microbiology; D014158:Transcription, Genetic; D014242:Trichoderma / Q000235:genetics / Q000254:growth & development / Q000378:metabolism / Q000502:physiology*