Melon (Cucumis melo L.) aquaporins as molecular markers of resistance to abiotic stresses and physiopathies

Abstract

Aquaporins are essential transmembrane proteins for life as they facilitate the passive transport of water and other molecules such as CO2, H2O2, nitrogenous compounds, or metalloids. In plants they have diversified into five subfamilies: PIPs (plasma membrane intrinsic proteins), TIPs (tonoplast intrinsic proteins), NIPs (nodulin-26-like intrinsic proteins), SIPs (small basic intrinsic proteins), and XIPs (uncharacterized intrinsic proteins). In addition, in plants, it knows that aquaporins help in the adaptation of stresses such as salinity, temperature, drought, or nutritional deficit and they could be involved in some physiopathies such as cracking, which consists of an imbalance between internal pressure and external part of the fruit, generating cracks on its surface and preventing its commercialization. That is why this Doctoral Thesis seeks to characterize the unknown aquaporins of the melon (Cucumis melo L.), one of the most produced fruits in Spain, especially in the southeast, and which is continuously subject to different environmental stresses. This objective was carried out by identifying the aquaporins that exist in melon plants by analysing their expression in different tissues, characterizing their response to typical abiotic stresses in the Region of Murcia, and studying their involvement in cracking. Furthermore, it was taken into account the most important physiological aspects and carried out a previous bioinformatic study to rename the existing aquaporins, as well as discard the fragments or repetitions. In the first chapter corresponding to the article entitled “Genome-wide analysis of the aquaporin genes in melon (Cucumis melo L.)”, the 31 melon aquaporins (2 PIP1s, 10 PIP2s, 8 TIPs, 8 NIPs, 2 SIPs) were identified. and 1 XIP) through phylogenetic analysis, we renamed them and eliminated duplications and errors in the databases, in addition to providing genomic information such as location or length. On the other hand, the possible transport was described based on the NPA motifs and variations, the ar/R selectivity filter, and the Froger’s positions. Finally, the basal expression levels of both root and leaf were analysed, highlighting some aquaporins such as CmPIP1;1, CmPIP1;2, or CmTIP1;1. In the second chapter that corresponds to the article entitled "Relationships between aquaporins gene expression and nutrient concentrations in melon plants (Cucumis melo L.) during typical abiotic stresses", the expression patterns of aquaporins were studied, in addition to different physiological parameters such as the potentials, mineral content or root hydraulic conductance of melon plants under salt stress, micronutrient deficiency, and high temperature. In general, in the three stresses, a generalized decrease in the expression of aquaporins could be observed, mainly in the root. Some aquaporins proved to be decisive in the different responses that these stresses produced, such as CmTIP1;1, which increased its expression in the root against salinity and high temperature, while it decreased in the leaf against stress due to nutrient deficiency. Finally, in the last chapter that corresponds to the article entitled "Aquaporins involvement in the regulation of melon (Cucumis melo L.) fruit cracking under different nutrient (Ca, B and Zn) treatments", two foliar treatments composed of B, Ca, and Zn and other composed of B and Zn, which both decreased the incidence of cracking in melons, 8.17% and 5.71% compared to an incidence of 17.61% in melons without treatments. Furthermore, these treatments were able to modify the expression of aquaporins in the melon pulp. Finally, it was possible to see how some aquaporins mainly related to water transport (CmPIP1;1, CmPIP1;2, CmPIP2;8, CmPIP2;10, CmTIP1;1, CmNIP2;2 and CmNIP5;1) were directly involved with the appearance of this pathophysiology.