TRANSCRIPTIONAL REGULATION OF THE CITRUS SINENSIS ABA-SIGNALOSOME DURING FRUIT DEHYDRATION

Water stress is an important factor affecting fruit quality. Since abscisic acid (ABA) is a key regulator of the dehydration response, understanding how the hormone is perceived will help to identify targets to improve drought hardiness in horticultural crops. To study the involvement of the ABA perception system in the dehydration response of citrus fruit, we have performed a comparative transcriptional analysis of the ABA-signalosome components in water-stressed fruit of ‘Navelate’ orange (Citrus sinensis (L.) Osbeck) and its fruit-specific ABA-deficient mutant ‘Pinalate’, which is more prone to dehydration. No significant differences in the expression levels of ABA receptors (CsPYR/PYL/RCAR) were found between wild-type and mutant fruit, while those of the negative regulators (CsPP2CA) were slightly lower in the mutant. Low differences in ABA receptors and downstream protein kinases (CsSnRK2s) transcript levels were found in response to dehydration. Contrarily, CsPP2CAs gene expression was highly regulated by ABA content and showed differences between cultivars, which suggest that CsPP2CAs play a key role regulating ABA response in citrus fruits to water stress. Results obtained by ABA application indicate that although the mutant may sense ABA, the hormone signal could be impaired because of reduced CsPP2CAs levels. Overall these results highlight these components as potential targets to improve drought hardiness in citrus fruits.