RNAseq reveals different transcriptomic responses to GA3 in early and midseason varieties before ripening initiation in sweet cherry fruits

Abstract

Gibberellin (GA) negatively affects color evolution and other ripening-related processes in non-climacteric fruits. The bioactive GA, gibberellic acid (GA(3)), 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 GA(3) delayed the IAD parameter (a ripening index) in a mid-season variety, whereas GA(3) 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 GA(3) applied on two sweet cherry varieties with different maturity time phenotypes. At harvest, GA(3) produced fruits with less color in both varieties. Similar to our previous report, GA(3) 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 GA(3)-treated fruits revealed that ripening-related categories were overrepresented in the early-season variety, including 'photosynthesis' and 'auxin response'. GA(3) 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 GA(3), which are negative regulators of ABA responses, and MYB44-like genes (putative repressors of PP2Cs expression) were downregulated. These results show that GA(3) differentially modulates the transcriptome at the onset of ripening in a variety-dependent manner and suggest that GA(3) 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.