Publication: Caracterización de los mecanismos moleculares de translocación de K+ y nuevos reguladores del transportador SlHAK5 en Solanum lycopersicum L
Authors
Martínez Martínez, Almudena
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Escuela Internacional de Doctorado
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Nieves Cordones, Manuel ; Rubio Muñoz, Francisco
Publisher
Universidad de Murcia
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DOI
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info:eu-repo/semantics/doctoralThesis
Description
Abstract
Objectives
K+ is an essential macronutrient for plants, involved in numerous physiological processes. In the current context, where it is necessary to develop varieties with improved nutrient uptake and use efficiency to address agronomic and environmental challenges, understanding the molecular mechanisms regulating K+ uptake and translocation is of particular relevance. Therefore, this doctoral thesis pursued three main objectives: (1) to study the role of the kinase SlCIPK9 in the regulation of the SlHAK5 transporter in tomato; (2) to analyze the function of the SlNRT1.5 transporter in K+ translocation from root to shoot; and (3) to identify new SlCIPK/SlCBL complexes involved in the activation of the SlHAK5 transporter.
Methodology
The above objectives were addressed through a combination of approaches, including heterologous expression assays in yeast and Xenopus laevis oocytes, bifluorescence assays to study protein–protein interactions, generation of knockout plants using CRISPR-Cas, hydroponic cultivation of tomato plants, determination of cation and anion content, pollen germination and tube elongation studies, as well as microscopy techniques.
Conclusions
The experimental work led to the following conclusions:1. slcipk9 mutant plants do not exhibit impaired K+ uptake or growth under low-K+ conditions, suggesting a limited role of SlCIPK9 in K+ nutrition in tomato. 2. SlCIPK9 is predominantly expressed in stamens, and its loss of function led to significantly shorter pollen tubes, revealing a specific role in pollen tube elongation. 3. The pollen phenotype observed in slcipk9 mutants occurs despite normal K+ content, indicating that SlCIPK9 regulates pollen tube elongation via a K+-independent mechanism. 4. SlNRT1.5 mediates K+ efflux when is expressed in Xenopus oocytes and, in tomato plants, it is expressed in multiple tissues, with particularly high expression in the root stele. 5. slnrt1.5 plants accumulate less K+ shoots than WT plants under low external pH (4.5) and limited K+ (0.05 mM) and N (0.5 mM) supply, indicating that SlNRT1.5 is a central component of K+ translocation, most likely by mediating K+ loading into the xylem vessels. 6. Further analyses of slskor slnrt1.5 double mutants reveal an overlapping role of SlSKOR and SlNRT1.5 to shoot K+ accumulation, with SlNRT1.5 playing a more prominent role under low-K+ conditions. 7. The targeted yeast complementation assay identify SlCIPK15 and SlCIPK26 as novel kinases capable of activating the high-affinity K+ transporter SlHAK5. Their functionality was confirmed through Rb+ uptake assays in yeast and BiFC interaction studies in Nicotiana. 8. Studies with slcipk15 knockout plants shows that this kinase plays an important role in pollen tube elongation but not in pollen germination. Unexpectedly, SlCIPK15 acts as a negative regulator of K+ translocation rather than as a positive regulator of SlHAK5-mediated K+ uptake. 9. Functional characterization of slcipk26 knockout lines reveals impaired pollen germination and phenotypes resembling those of slhak5 mutants, suggesting that SlCIPK26 regulates SlHAK5 in reproductive tissues. In contrast, in roots SlCIPK26 does not appear to play a major role in SlHAK5-mediated K+ transport.
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Citation
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29-nov-2026
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