Copper (Cu) plays a key role as cofactor in the plant proteins participating in essential cellular processes, such as electron transport and free radical scavenging. Despite high-affinity Cu transporters (COPTs) being key participants in Cu homeostasis maintenance, very little is known about COPTs in tomato (Solanum lycopersicum) even though it is the most consumed fruit worldwide and this crop is susceptible to suboptimal Cu conditions. In this study, a six-member family of COPT (SlCOPT1-6) was identified and characterized. SlCOPTs have a conserved architecture consisting of three transmembrane domains and β-strains. However, the presence of essential methionine residues, a methionine-enriched amino-terminal region, an Mx₃Mx₁₂Gx₃G Cu-binding motif and a cysteine rich carboxy-terminal region, all required for their functionality, is more variable among members. Accordingly, functional complementation assays in yeast indicate that SlCOPT1 and SlCOPT2 are able to transport Cu inside the cell, while SlCOPT3 and SlCOPT5 are only partially functional. In addition, protein interaction network analyses reveal the connection between SlCOPTs and Cu P_IB-type ATPases, other metal transporters, and proteins related to the peroxisome. Gene expression analyses uncover organ-dependency, fruit vasculature tissue specialization and ripening-dependent gene expression profiles, as well as different response to Cu deficiency or toxicity in an organ-dependent manner.

The LED Blue Light (LBL) (450 nm) effect on hormones levels and on jasmonates (JAs) metabolism in oranges was investigated. The quantum flux (2 days, 60 μmol m^-2. s^-1) was chosen for its efficacy in reducing postharvest rot caused by this crop's main postharvest phytopathogenic fungus (Penicillium digitatum). The analysis of abscisic (ABA), salicylic (SA) and indole-3-acetic (IAA) acids, and of JAs-related metabolites, revealed that LBL modifies all studied metabolites and had major effects on JAs levels, mainly on jasmonic acid (JA) and its precursor cis-(+)-12-oxo-phytodienoic acid (OPDA). This agrees with the up-regulation of the genes participating in their synthesis. Results highlight the relevance of CsLOX1 and CsLOX5, and the contribution of CsAOC3, in the LBL-induced OPDA biosynthesis, whereas CsOPR2, CsACX1 and CsACX3 would play a part in the synthesis of JA from OPDA. Data also suggest that the applied LBL quantum flux favors fruit JA perception by increasing the expression of the coronatine insensitive 1 (COI1) receptor; and signaling by down-regulating abundant CsJAZ negative regulators. Differences in OPDA and JA between the LBL-treated oranges and their control fruit left in the dark disappeared after shifting the LBL-treated oranges to darkness for 3 more days. However, the LBL and darkness combination slightly increased IAA and SA contents.

Phospholipases (PLs) are key enzymes involved in membrane remodeling, structure, and signaling during plant stress responses. This study analyzed early and long-term transcriptional regulation of PL isoforms—PLD (CsPLDα,β,δ,γ,ζ), PLA (CsPLA₂α,₂β, CsPAT1), and PLC (CsNPC3, CsPI-PLC)—in Fortune mandarins exposed to thermal stress. Three conditions were evaluated: heat stress (37 °C, 90–95% relative humidity), cold stress (2 °C), and cold stress in fruit exposed to a prior heat conditioning treatment (3 days at 37 °C) that reduces chilling injury (CI). All genes—except CsNPC3—were rapidly upregulated by heat (4–12 h), suggesting a role as early heat sensors and their putative participation in the heat-induced chilling tolerance. Moreover, after transferring heat-conditioned fruit to cold, CsPLDζ, CsPI-PLC, and CsNPC3 showed marked expression increases, highlighting their relevance in such cross-adaptation. In non-conditioned fruit, CsPLDγ was strongly and consistently induced by cold and associated with CI development, as further confirmed by tissue-specific analysis comparing necrotic and healthy flavedo. Conversely, cold-induced CsPLDα, CsPLDζ, CsPLA₂α, and CsNPC3 may contribute to protective responses via early signaling cascades; although CsPLA₂α might contribute to CI only by 60 days. These findings highlight the isoform-specific and time-dependent regulation of PL genes under thermal stress and their potential role in citrus stress tolerance.

It is known that nutrient deprivation following detachment can cause non-chilling peel pitting (NCPP) in citrus fruits when stored under a non-stressful environment and that this damage is reduced by pretreating the fruit with ethylene (ETH) (4 d, 10 µL L⁻¹). The present work investigates the effect of this pretreatment on jasmonate (JA) accumulation and transcriptional regulation in mature Navelate oranges (Citrus sinensis L. Osbeck) stored under non-stressful conditions. ETH increased the expression of abundant genes participating in the synthesis of cis-(+)-12-oxo-phytodienoic acid (OPDA), jasmonic acid (JA), and methyl jasmonate (MeJA). ETH also upregulated genes involved in jasmonoyl–isoleucine (JAIle) synthesis (CsJAR1) and decrease (CsCYP94B3 and CYP94C1), and CsSTA2, related to JA sulfation. The levels of these JA metabolites increased during fruit holding in ETH and after shifting them to air, with MeJA accumulation being especially remarkable. Overall, the beneficial effect of ETH on reducing NCPP appears to be related not only to this redirection of OPDA and JA metabolism towards the formation of JA derivatives but also to the regulation of JA signalling. Indeed, the repression of the receptor CsCOI1 and upregulation of various CsJAZs repressors caused by nutrient deprivation, together with the ETH-mediated induction of CsCOI1, CsTOPLESS, and abundant CsJAZs during long-term storage, suggests the occurrence of an ETH-enhanced negative transcriptional regulatory feedback loop in JA metabolism and signalling, by which the susceptibility of detached Navelate oranges to NCPP might be reduced.