Gibberellic Acid Modifies the Transcript Abundance of ABA Pathway Orthologs and Modulates Sweet Cherry (Prunus avium) Fruit Ripening in Early- and Mid-Season Varieties

Abstract

Several phytohormones modulate ripening in non-climacteric fruits, which is triggered by abscisic acid (ABA). Gibberellins (GAs) are present during the onset of ripening in sweet cherry fruits, and exogenous gibberellic acid (GA₃) application delays ripening, though this effect is variety-dependent. Although an ABA accumulation delay has been reported following GA₃ treatment, the mechanism by which GA modulates this process has not been investigated at the molecular level in sweet cherry. Therefore, the aim of this work is to analyze the effect of GA₃ on the fruit ripening process and the transcript levels of ABA pathway orthologs in two varieties having different maturity time phenotypes. The early-season variety had a rapid transition from yellow to pink fruit color, whereas pink color initiation took longer in the mid-season variety. GA₃ increased the proportion of lighter colored fruits at ripeness in both varieties, but it produced a delay in IAD-a ripening index-only in the mid-season variety. This delay was accompanied by an increased transcript abundance of PavPP2Cs, which are putative negative regulators of the ABA pathway. On the other hand, the early-season variety had increased expression of PavCYP707A2-a putative ABA catabolic gene-, and reduced transcript levels of PavPP2Cs and SnRK2s after the GA₃ treatment. Together these results show that GA modulates fruit ripening, exerting its action in part by interacting with the ABA pathway in sweet cherry.

Keywords: GA3; IAD; abscisic acid; fruit tree management; gibberellin; non-climacteric; ripening; sweet cherry.

Figure 1

Fruit growth and growth rate curves of early-season variety, Glenred (A) and mid-season variety, Lapins (B). A color scale is included based on fruit phenology (Tables S1 and S2). Growth resumption prior to fruit color change is indicated with a dotted blue line, 20 fruits from Lapins and Glenred were randomly selected for measurements. Data as ± SEM. DAFB, days after full bloom.

Figure 2

Effect of exogenous gibberellic acid (GA₃) on fruit growth of early-season variety, Glenred (A) and mid-season variety, Lapins (B) 20 fruits from control and GA₃ trees of Lapins and Glenred were randomly selected for measurements. Data as ± SEM ANOVA with Tukey’s post hoc test at p < 0.05 was conducted; “*” denotes statistical differences between GA₃-treated and control fruits. DAFB, days after full bloom.

Figure 3

Effect of GA₃ on color distribution and index of absorbance difference (IAD) at harvest of early-season variety, Glenred (A,B) and mid-season variety, Lapins (C,D). 20 fruits from control and GA₃ trees of Lapins and Glenred were randomly selected for nondestructive IAD measurements in the field and 25 fruits for color distribution assessment at harvest. Data as ± SEM ANOVA with Tukey’s post hoc test at p < 0.05 was conducted; “*” denotes statistical differences between GA₃-treated and control fruits CTIFL (Centre Technique Interprofessionnel des Fruits et Légumes) color chart was used in (B,D), where 1 is the lightest color, and 4 is the darkest color, respectively (Figure S3). DAFB, days after full bloom.

Figure 4

Effect of GA₃ on transcript abundance relative to PavCAC of PavNCED1 and PavCYP707A2 sweet cherry orthologs, 5 days after the treatment (T5). Fruits from control and GA₃ trees of (A) early-season variety Glenred and (B) mid-season variety Lapins, were randomly selected and pooled for the RT–qPCR analyses. Data as +SEM. Relative transcript abundance was set to 1.0 at T0, where T0 is the sampling performed immediately before GA₃ application ANOVA with Tukey’s post hoc test at p < 0.05 was conducted; “*” denotes statistical differences between GA₃-treated and control fruits for a gene.

Figure 5

Effect of GA₃ on transcript abundance relative to PavCAC of PavPP2C and PavSnRK2 sweet cherry orthologs, 5 days after the treatment (T5). Fruits from control and GA₃ trees of (A) early-season variety Glenred and (B) mid-season variety Lapins were randomly selected and pooled for the RT–qPCR analyses. Data as +SEM. Relative transcript abundance was set to 1.0 at T0, where T0 is the sampling performed immediately before GA₃ application ANOVA with Tukey’s post hoc test at p < 0.05 was conducted; “*” denotes statistical differences between GA₃-treated and control fruits for a gene.