Anti-auxin treatment and co-expression networks reveal auxin involvement in the transition to ripening in sweet cherry fruits.

The transition from development to ripening is governed by several hormones that interplay with abscisic acid (ABA) in non-climacterics, including auxin. In sweet cherry (Prunus avium), auxin has been shown to promote fruit coloration and ABA accumulation, in contrast to other non-climacteric models. Thus, this work aims to explore the role of auxin during the transition to ripening in sweet cherry by assessing the global gene expression response to an auxin homeostasis disturbance. For this, we used 5d, a fluorescently labeled compound with previously reported anti-auxin activity, which was applied to fruits at the light-green stage. This compound desynchronized fruit coloring and ripening, as fruit coloration and IAD were enhanced, while softening and soluble solid content increase were delayed. Enriched functional categories in the treatment were related to auxin export, signaling and response, flavonol biosynthesis, malate transport, inositol metabolism, and cell wall organization. A subset of genes downregulated by the anti-auxin 5d contributed to the enrichment of categories associated with ABA response. Anti-auxin 5d prevented ABA increase observed in control fruits, upregulated ABA receptor genes, and altered ABA-responsive gene expression, supporting auxin-ABA crosstalk. The treatment with the anti-auxin 5d also upregulated genes related to gibberellin (GA) biosynthesis, suggesting that auxin may influence ripening through modulation of GA production. Co-expression analyses revealed that auxin-related genes encoding SAUR72 and PIN-LIKES 3-like were anchors, having connections with ripening-related genes, including those involved in ABA response and degradation, cell wall softening and hormone methylation, further supporting a pro-ripening role for auxin in sweet cherry.