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A genetic regulatory network controlling floral transition in apple
Conference presentation

A genetic regulatory network controlling floral transition in apple

Kwanho Jeong, Virginia Fernández, Mohamad Al Bolbol, Joan Estevan, Samer El Khoury, Alexandre Soriano, Gautier Sarah, Gaetan Droc, Evelyne Costes and Fernando Andrés
The Workshop on Molecular Mechanisms Controlling Flowering 2024 (Palermo, Italy, 16/06/2024–20/06/2024)
19/06/2024

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Abstract

The floral transition is regulated by both environmental and endogenous cues. In many fruit tree species, floral transition is inhibited by the present of fruits, which are believed to be the source of an inhibitory systemic signal that represses the floral induction of adjacent meristems. This could result in biennial bearing, a phenomenon where trees produce an irregular crop load from one year to the next. Therefore, understanding the control of flowering is crucial to ensure fruit security and improve fruit production. In the model plant species Arabidopsis thaliana, an intricate genetic regulatory network (GRN) governing floral transition relies on a fine-tuned interplay among members of the SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) and APETALA2-like (AP2-like) gene families, microRNAs belonging to the miR156 and miR172 families, and the plant hormone gibberellin (GA), whose molecular signalling is mediated by the activity of the DELLA proteins. To date, whether this genetic network operates in fruit tree species remains unknown. In this study, we aim at deciphering a GRN that controls floral transition in apple (Malus domestica Borkh.) and identifying potential fruit-derived systemic signals that inhibit floral transition. Supporting the involvement of the SPL-miR156/AP2-like-miR172 floral regulatory motif, orthologues of SPL5 and SPL9 (MdSPL5 and MdSPL9, respectively) are transcriptionally activated in buds of apple trees during the floral transition. We have conducted a comprehensive miRNA sequencing and found an apple miR156 member that may act as a seed-derived signal to suppress MdSPL9 expression in buds. Furthermore, we have gained insights into the apple floral GRN by identifying genome-wide transcriptional targets of MdSPL and MdAP2-like transcription factors. Finally, we have found that MdSPL9 interacts with a DELLA-like protein potentially involved in the GA-mediated floral repression in apple. Altogether, these results allow us to draft a novel GRN involved in the floral transition of apple tree.

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