Jasmonates in the Ethylene-Induced Resistance of Detached Citrus Fruits to Peel Damage

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 (<i>Citrus sinensis</i> L. Osbeck) stored under non-stressful conditions. ETH increased the expression of abundant genes participating in the synthesis of <i>cis</i>-(+)-12-oxo-phytodienoic acid (OPDA), jasmonic acid (JA), and methyl jasmonate (MeJA). ETH also upregulated genes involved in jasmonoyl-isoleucine (JAIle) synthesis (<i>CsJAR1</i>) and decrease (<i>CsCYP94B3</i> and <i>CYP94C1</i>), and <i>CsSTA2</i>, 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 <i>CsCOI1</i> and upregulation of various <i>CsJAZs</i> repressors caused by nutrient deprivation, together with the ETH-mediated induction of <i>CsCOI1</i>, <i>CsTOPLESS</i>, and abundant <i>CsJAZs</i> 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.