Function of microRNAs in plant innate immunity /
- Autores: Rosany del Carmen Camargo Ramírez
- Directores de la Tesis: Blanca San Segundo de los Mozos (dir. tes.)
- Lectura: En la Universitat Autònoma de Barcelona ( España ) en 2017
- Idioma: español
- Tribunal Calificador de la Tesis: Teresa Altabella Artigas (presid.), Soledad Martos Arias (secret.), Julio Luis Rodríguez Romero (voc.)
- Programa de doctorado: Programa de Doctorado en Biología y Biotecnología Vegetal por la Universidad Autónoma de Barcelona
- Materias:
- Enlaces
- Resumen
Plants have an innate immunity system that allows them to defend themselves against infection by pathogens. The defense response involves an important reprogramming of gene expression in the plant and transcriptional activation of genes coding for: i) Proteins and compounds with antimicrobial activity; ii) Regulatory proteins of defense response (i.e. transcription factors and other transcription regulators, protein kinases, etc.); and iii) proteins/enzymes implicates in hormone signaling associated with the defense response. The current view of the immune response of plants is that, in addition to the mechanisms of transcriptional regulation of gene expression in the plant defense response, also involves mechanisms of post-transcriptional regulation that are regulated by small RNAs.
microRNAs (miRNAs) are a class of small non-coding RNAs that regulate gene expression at the post-transcriptional level by degradation or translational repression of their target genes. The regulatory function of miRNAs in processes associated with plant growth and development is widely described. However, available information about the involvement of miRNAs in plant defense against pathogens is more limited.
This thesis comprises the study of miRNAs in innate immunity in plants. The work has been developed in rice (Chapter I and Chapter II) and in Arabidopsis (Chapter III), model systems used in studies of functional genomics in monocotyledonous and dicotyledonous species, respectively. Chapter I describes the functional identification and characterization of new rice miRNAs in their interaction with the fungus Magnaporthe oryzae. This fungus is responsible for blast disease, one of the most devastating diseases for rice cultivation worldwide. From the information generated by high-throughput sequencing of small rice RNA libraries, candidate sequences to represent novel rice miRNAs were selected. In this work 5 of these candidates have been studied (miR-64, miR-75, miR-96, miR-98 and miR-203). Obtaining transgenic rice lines has demonstrated that the overexpression of MIR-64 and MIR-75 confers resistance to M. oryzae, therefore these miRNAs function as positive regulators in the rice immune response. Moreover, overexpression of MIR-96, MIR-98 or MIR-203 increase susceptibility to M. oryzae in rice plants (negative regulators of immune response). Analysis of rice mutants affected in the miRNA biogenesis (dcl1, dcl3 and dcl4 mutants) indicate that the mature miRNA production of miR-64, miR-75 or miR-96 depends on DCL3 and/or DCL4, which supports the idea that they are novel rice miRNAs. Furthermore, by gene editing using CRISPR/Cas9, it has been found that a 22 nucleotides deletion in miR-75 precursor results in a susceptibility phenotype under M. oryzae infection (Chapter II), in agreement with a resistance phenotype that was observed in overexpressor plants for this miRNA.
In chapter III, the miR858 function in Arabidopsis thaliana innate immunity to infection by pathogenic fungi was studied. This miRNA represses the expression of MYB transcription factors, which act as activators of the expression of genes involved in flavonoids biosynthesis. Plants are resistant to infection by pathogenic fungi (Plectosphaerella cucumerina, Fusarium oxysporum f. sp. Conglutinans and Colletotrichum higginsianum) when the activity of miR858 is blocked by the expression of target mimicry (MIM858 plants), while the overexpression of this miRNA confers greater susceptibility to infection. Additionally, interference with miR858 activity and consequent increase of MYB gene expression in MIM858 plants significantly affects phenylpropanoids metabolism, favoring the synthesis and accumulation of flavonoids, and disfavoring the synthesis of lignin precursors. The antifungal activity that was observed for Kaempferol, naringenin (flavonoids) and p-Coumaric acid, would explain the resistant phenotype by fungi infection which is observed in the MIM858 plants.
Altogether, the results obtained in this work demonstrate that miRNAs are an important component in the resistance/susceptibility to infection by pathogenic fungi in Arabidopsis and rice plants. Greater knowledge of miRNA function in plant innate immunity and processes that are regulate by these riboregulators, can be useful in the design of new strategies for the control of diseases in plants.
