Differential expression of the Citrus sinensis ABA perception system genes during postharvest fruit dehydration

Water stress occurring during postharvest handling and storage is an important factor affecting external quality of fresh fruit and vegetables. The phytohormone abscisic acid (ABA) is a key regulator of the dehydration response in citrus fruit, which are prone to develop peel damage in response to water stress. To study the involvement of the ABA perception system in the dehydration response and its relationship with the occurrence of peel damage in citrus fruit, a comparative transcriptional analysis of the ABA signalling core components in water-stressed fruit of the wild-type ‘Navelate’ orange (Citrus sinensis L. Osbeck) and its spontaneous fruit-specific ABA-deficient mutant ‘Pinalate’, which is more susceptible to dehydration and to develop non-chilling peel pitting (NCPP), has been performed. Minor differences in ABA receptors (CsPYR/PYL/RCAR) and downstream protein kinase (CsSnRK2) transcript levels were found in response to dehydration between wild-type and the ABA-deficient mutant fruit. In contrast, the expression of the ABA-mediated PYR/PYL/RCAR-inactivated clade A protein phosphatases 2C (CsPP2CA) was highly regulated by ABA content and showed significant differences between cultivars. Results obtained by ABA application suggest the involvement of these negative regulators in the impaired response of ‘Pinalate’ fruit to water stress. Overall, the higher responsiveness to ABA changes of the CsPP2CAs during citrus fruit dehydration highlights these components as key regulator control points in the response of citrus fruit to water stress.