Loss of firmness is one of the main factors limiting the storability and commercial quality of sweet cherries, fruits that are particularly susceptible to softening during ripening and postharvest storage. Understanding the molecular mechanisms regulating cell wall degradation is therefore of strategic importance for the development of management technologies and breeding strategies.
A recent study from China provides important insights in this regard, clarifying the role of ethylene and the transcription factor PavSPL7 in regulating fruit softening, while highlighting a sophisticated negative feedback system linking hormonal signaling and gene regulation.
The results showed that, during fruit development and ripening, the content of ACC, a direct precursor of ethylene, progressively increases and is accompanied by a significant reduction in fruit firmness. Exogenous ethylene treatments further accelerate this process, inducing a marked decrease in fruit firmness and increasing the expression of genes involved in cell wall degradation, including PavEXPA6, PavPMEI2, and PavPL8, as well as PavACS7, a key gene involved in ethylene biosynthesis.
These findings confirm the active role of ethylene even in a non-climacteric species such as sweet cherry, reinforcing the hypothesis that this hormone plays a regulatory role during the final stages of ripening.
A central finding of the study is the identification of the transcription factor PavSPL7 as a key repressor of the softening process. PavSPL7 expression is high during the early stages of fruit development and progressively declines during ripening; this reduction is further enhanced by ethylene treatment, suggesting direct negative regulation by the hormone.
Functionally, overexpression of PavSPL7 in sweet cherry fruits results in increased firmness, reduced ACC levels, and lower degradation of cell wall components, particularly soluble pectins. At the same time, transcriptional repression of key genes involved in both cell wall loosening and ethylene biosynthesis was observed.
Molecular analyses demonstrated that PavSPL7 acts directly by binding to GTAC motifs within the promoters of target genes, exerting a repressive effect on their transcription. In this way, PavSPL7 limits both cell wall degradation and ethylene production, functioning as a dual-level negative regulator. This effect was also confirmed in heterologous tomato systems, where overexpression of the gene delayed ripening, increased fruit firmness, and reduced ethylene accumulation.
The model proposed by the researchers describes a negative feedback loop in which ethylene and PavSPL7 act antagonistically. During the early stages of fruit development, low ethylene levels allow high PavSPL7 expression, which represses genes responsible for fruit softening. As ripening progresses, increased ethylene production suppresses PavSPL7 expression, relieving transcriptional repression and activating cell wall degradation and further hormone biosynthesis, thereby accelerating fruit softening.
From an applied perspective, these findings offer promising opportunities for postharvest quality management and sweet cherry breeding. PavSPL7 appears to be a potential molecular target for modulating fruit firmness and extending shelf life, thereby helping to reduce losses along the supply chain.
Source: Sun, Y., Xiao, Y., Zhang, X., Du, B., Turupu, M., Wang, X., Zhang, Q., Yao, Q., & Li, T. (2026). Ethylene promotes pectin degradation and fruit softening by negatively regulating PavSPL7 in sweet cherry (Prunus avium). Horticulture Advances, 4(1), 1. https://doi.org/10.1007/s44281-025-00089-0
Image source: Stefano Lugli
Andrea Giovannini
PhD in Agricultural, Environmental and Food Science and Technology - Arboriculture and Fruitculture, University of Bologna, IT
25 Jun 2024
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