Abstract
Fruit ripening and abscission are the results of the cell wall modification concerning different components of the signaling network. However, molecular-genetic information on the cross-talk between ripe fruit and their abscission zone (AZ) remains limited. In this study, we investigated transcriptional and hormonal changes in olive (Olea europaea L. cv Picual) pericarp and AZ tissues of fruit at the last stage of ripening, when fruit abscission occurs, to establish distinct tissue-specific expression patterns related to cell-wall modification, plant-hormone, and vesicle trafficking in combination with data on hormonal content. In this case, transcriptome profiling reveals that gene encoding members of the α-galactosidase and β-hexosaminidase families associated with up-regulation of RabB, RabD, and RabH classes of Rab-GTPases were exclusively transcribed in ripe fruit enriched in ABA, whereas genes of the arabinogalactan protein, laccase, lyase, endo-β-mannanase, ramnose synthase, and xyloglucan endotransglucosylase/hydrolase families associated with up-regulation of RabC, RabE, and RabG classes of Rab-GTPases were exclusively transcribed in AZ-enriched mainly in JA, which provide the first insights into the functional divergences among these protein families. The enrichment of these protein families in different tissues in combination with data on transcript abundance offer a tenable set of key genes of the regulatory network between olive fruit tissues in late development.
Highlights
In fleshy fruit, the fruit ripening and abscission are developmentally regulated and genetically programmed processes [1], whose induction depends on a complex interplay of a plant’s hormone content in addition to factors that alter the sensitivity of the tissues [2,3,4,5,6,7]
Fully ripe fruit have marked physiological differences with respect to their abscission zone (AZ), both fruit ripening and abscission processes are the result of the cell wall modification, which involves a wide range of structural proteins and hydrolytic enzymes with distinct functions in the tissues, which concerns common and different components of the signaling network playing either direct or indirect roles in these processes
We have shown that the changes detected in AZ cell wall polysaccharides during ‘Picual’ fruit abscission are related to pectic polysaccharide de-esterification and solubilization [25], which is likely promoted by cell wall-associated pectin methyl esterases (PMEs) and polygalacturonases (PGs) enzymes
Summary
The fruit ripening and abscission are developmentally regulated and genetically programmed processes [1], whose induction depends on a complex interplay of a plant’s hormone content in addition to factors that alter the sensitivity of the tissues [2,3,4,5,6,7]. The study of gene function in the olive has been fundamentally advanced by the availability of whole genome sequences [10,11,12], while several transcriptomic, proteomic, and metabolic studies have been developed in olive fruit [13,14,15,16,17,18,19]. These studies concern only a few genotypes and little is still known about olive-fruit biology. Information concerning the plant hormone composition of the olive fruit remains to be determined
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