Abstract
Gibberellin (GA) negatively affects color evolution and other ripening-related processes in non-climacteric fruits. The bioactive GA, gibberellic acid (GA3), is commonly applied at the light green-to-straw yellow transition to increase firmness and delay ripening in sweet cherry (Prunus avium L.), though causing different effects depending on the variety. Recently, we reported that GA3 delayed the IAD parameter (a ripening index) in a mid-season variety, whereas GA3 did not delay IAD but reduced it at ripeness in an early-season variety. To further explore this contrasting behavior between varieties, we analyzed the transcriptomic responses to GA3 applied on two sweet cherry varieties with different maturity time phenotypes. At harvest, GA3 produced fruits with less color in both varieties. Similar to our previous report, GA3 delayed fruit color initiation and IAD only in the mid-season variety and reduced IAD at harvest only in the early-season variety. RNA-seq analysis of control- and GA3-treated fruits revealed that ripening-related categories were overrepresented in the early-season variety, including ‘photosynthesis’ and ‘auxin response’. GA3 also changed the expression of carotenoid and abscisic acid (ABA) biosynthetic genes in this variety. In contrast, overrepresented categories in the mid-season variety were mainly related to metabolic processes. In this variety, some PP2Cs putative genes were positively regulated by GA3, which are negative regulators of ABA responses, and MYB44-like genes (putative repressors of PP2Cs expression) were downregulated. These results show that GA3 differentially modulates the transcriptome at the onset of ripening in a variety-dependent manner and suggest that GA3 impairs ripening through the modification of ripening associated gene expression only in the early-season variety; whereas in the mid-season variety, control of the ripening timing may occur through the PP2C gene expression regulation. This work contributes to the understanding of the role of GA in non-climacteric fruit ripening.
Highlights
Gibberellin (GA) negatively affects color evolution and other ripening-related processes in nonclimacteric fruits
Some GAs oxidase genes change their expression at veraison compared to the previous stage in grapevine fruits11. GA3 treatment at veraison delays ripening and affects the transcript levels of putative PP2Cs, which are negative regulators of abscisic acid (ABA) s ignaling[12]
Several GAs are present at the time of fruit color initiation in sweet cherry and other non-climacteric fruits[5,10]; we aimed to investigate the role of GA in ripening triggering by altering GA homeostasis
Summary
Gibberellin (GA) negatively affects color evolution and other ripening-related processes in nonclimacteric fruits. Similar to our previous report, GA3 delayed fruit color initiation and IAD only in the mid-season variety and reduced IAD at harvest only in the early-season variety. Overrepresented categories in the mid-season variety were mainly related to metabolic processes In this variety, some PP2Cs putative genes were positively regulated by GA3, which are negative regulators of ABA responses, and MYB44like genes (putative repressors of PP2Cs expression) were downregulated. Kuhn et al.[17] reported that the Index of Absorbance Difference (IAD), a ripening index, was delayed after the GA3 treatment only in a mid-season variety, whereas the treatment reduced the IAD only at harvest in an early-season variety; interestingly, both varieties presented modified expression of ABA pathway-related genes. Despite the available information on the participation of GA in the fruit ripening process, the effect of this hormone has been barely explored at the whole gene expression level during the sweet cherry fruit ripening
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