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Esta tesis doctoral se centra en la caracterizacion de genes MTV que estan implicados en trafico vacuolar en Arabidopsis. La vacuola es un organulo esencial en las estrategias adaptativas de las plantas y tiene una gran importancia agronomica y biotecnologica por su capacidad de almacenamiento de proteinas esenciales para la nutricion humana o de proteinas recombinantes de uso biotecnologico. En esta tesis se han estudiado dos mutantes modificados en trafico a vacuolas (mutantes mtv) y se han identificado mutaciones puntuales en los genes MTV9/Atlg24560 y MTV11/At4g29380 como las causantes de los defectos en trafico vacuolar. El gen MTV9 es especifico de plantas y codifica una proteina que se localiza en el compartimento prevacuolar, posiblemente dirigida a ese compartimento por la palmitoilacion de una cisteina presente en su extremo C-terminal. La sobreexpresion de MTV9 provoca la agregacion de los compartimentos prevacuolares y la deslocalizacion de proteinas SNARE, interfiriendo con el trafico de proteinas a vacuolas pero no con la secrecion de proteinas de membrana plasmatica. Estos resultados indican que MTV9 es esencial para el trafico a vacuolas y podria estar implicado en procesos de anclaje de vesiculas u organulos con el compartimento prevacuolar para mediar su fusion. El gen MTV11 codifica para el ortologo de la proteina VPS15, que forma parte de un complejo fosfatidilinositol-3-kinasa (PI3K), cuya actividad es necesaria para todas las rutas de trafico a vacuola en levaduras y animales. El gen MTV11 es esencial en plantas y su disrupcion causa letalidad en polen. El mutante mtvll-1 aislado en esta tesis es un alelo hipomorfico que ha permitido estudiar el papel de este gen en el desarrollo de Arabidopsis. Mediante el uso del biomarcador 2xFYVE hemos obtenido evidencias de que la sintesis de fosfatidilinositol-3-fosfato esta disminuida considerablemente en el mutante, indicando que el alelo mutante reduce la actividad del complejo PI3K. El mutante mtvll-1 tiene afectado el trafico de proteinas vacuolares de reserva en semillas y el reciclaje de proteinas de membrana plasmatica en la vacuola. Estos defectos provocan una disminucion en el crecimiento y alteraciones en la filotaxia en condiciones normales de crecimiento. Ensayos de resistencia a estreses abioticos han demostrado que las plantas mtvll-1 son mas tolerantes a altas concentraciones de arsenato, un compuesto que se secuestra en vacuolas una vez es reducido a arsenito en el citosol. Este descubrimiento puede tener importantes implicaciones en el desarrollo de plantas mejoradas para la fitoremediacion de suelos contaminados con arsenico. ABSTRACT This doctoral thesis adresses the characterization of MTV genes that are involved in vacuolar trafficking in Arabidopsis. The vacuole is an essential organelle for adaptative strategies of plants and has a great agronomic and biotechnological importance for its storage capacity of essential proteins for human nutrition or of recombinant proteins for biotechnological purposes. In this thesis, two mutants modified in trafficking to vacuole (mtv mutants) have been studied and point mutations in the MTV9 / At1g24560 and MTV11 / At4g29380 genes have been identified as the responsibles for the defects in vacuolar trafficking. The MTV9 gene is plant-specific and encodes a protein that is located at the prevacolar compartment, possibly directed to that compartment by the palmitoylation of a cysteine present at its C-terminal end. The overexpression of MTV9 provokes the aggregation of the pre-vacuolar compartments and the delocalization of SNARE proteins, interfering with the trafficking of proteins to vacuoles but not with the secretion of plasma membrane proteins. These results indicate that MTV9 is essential for the trafficking to vacuoles and could be involved in anchoring processes of vesicles or organelles with the prevacuolar compartment to mediate their fusion. The MTV11 gene encodes for the ortholog of the VPS15 protein, which is part of a phosphatidylinositol-3-kinase (PI3K) complex, whose activity is required for all vacuolar related trafficking routes in yeasts and animals. The MTV11 gene is essential in plants and its disruption causes lethality in pollen. The mutant mtv11-1 isolated in this thesis is a hypomorphic allele that has allowed to study the role of this gene in Arabidopsis growth and development. By using the biomarker 2xFYVE we have obtained evidence that the synthesis of phosphatidylinositol-3- phosphate is significantly decreased in the mutant, indicating that the mutant allele reduces the activity of the PI3K complex. The mutant mtv11-1 has affected the trafficking of storage proteins in seeds reservoirs and the recycling of plasma membrane proteins. These defects cause a decrease in growth and alterations in phyllotaxis under normal growth conditions. Moreover, different assays to study resistance to abiotic stresses performed in the mtv11-1 mutant, have shown that mtv11-1 plants are more tolerant to high concentrations of arsenate, a compound that is sequestered in vacuoles once it is reduced to arsenite in the cytosol. This discovery may have important implications for the development of improved plants in phytoremediation of soils contaminated with arsenic.

Caracterización funcional de las proteínas MTV9 y MTV11 y su implicación en el tráfico vacuolar