We evaluated the physiological and biochemical changes in the plant as consequence of plant growth under suboptimal Cu availability throughout in vitro, hydroponics and greenhouse assays. Root and shoot lengths were significantly reduced, as well as the dry weight and biomass per plant. Also the number of flowers and the total yield was diminished as consequence of Cu deficiency conditions. In terms of external fruit quality and nutritional status, deficient Cu availability did not alter color evolution during the fruit ripening process but advanced fruit softening rate and increased internal acidity after harvest. In turn, this stress increased the antioxidant capacity of the fruit, probably due to increased vitamin C content, but had little effect on total phenolic, flavonoids and lycopene contents. Also, the incidence of fruit cracking and the susceptibility to pathogen infection increased in the fruit harvested from plants grown under Cu deficient conditions. Last, the contents of important micronutrients for human health, such as Cu and Fe, were changed in response to Cu deficiency stress conditions. These results have been divided in two different manuscripts and presented in the International Symposiums and in several diffusion seminars.
We also studied the molecular mechanisms underlying the Cu deficiency stress response in tomato plants and fruit. Six members of the copper transporters family were identified (SlCOPT1-6) and their secondary and tertiary structures, as well as the potential interaction network and gene expression patters were analyzed. Also, we assayed their functionality through complementation expression assays in yeast. These results point altogether that SlCOPT1 and SlCOPT2 are completely functional and the most ubiquitously expressed COPTs in the plant and fruit tissues. On the other hand, the expression of SlCOPT3 and SlCOPT5 is specialized in stem and fruit tissues. These results are already published (10.1016/j.ijbiomac.2021.10.032) and have been presented in the 6th ABS International Conference through an invited speech. In parallel, we have compared the transcriptome of different tissues (root, stem, leaf and fruit) of plants grown under Cu sufficiency and deficiency conditions. New generation sequencing results uncovered a set of common responses mainly directed to increase the Cu uptake in the root and to enhance its mobilization to upper parts of the plant.The major SlCOPT carrying out such functions was SlCOPT2, which point out this Cu transporter as the most plausible target for biotechnological improvement of Cu intake and distribution in tomato plants through genome-editing technologies. These results will be published in two independent manuscripts. On the other hand, the comparative transcriptomic analysis of the fruit harvested at the red ripe (commercial) ripening stage has revealed that this organ is not regulating a high number of biological processes in response to the Cu deficiency stress. These data are very valuable since they have allowed identifying fruit-specificities in the regulation of Cu homeostasis-related genes. This has a promising biotechnological potential in order to improve/optimize the micronutritional content of this product, which might has an impact on human diet and hence in human health.
