A Complex Gene Network Mediated by Ethylene Signal Transduction TFs Defines the Flower Induction and Differentiation in Olea europaea L.

The olive tree (Olea europaea L.) is a typical Mediterranean crop, important for olive and oil production. The high tendency to bear fruits in an uneven manner, defined as irregular or alternate bearing, results in a significant economic impact for the high losses in olives and oil production. Buds from heavy loaded ('ON') and unloaded ('OFF') branches of a unique olive tree were collected in July and the next March to compare the transcriptomic profiles and get deep insight into the molecular mechanisms regulating floral induction and differentiation. A wide set of DEGs related to ethylene TFs and to hormonal, sugar, and phenylpropanoid pathways was identified in buds collected from 'OFF' branches. These genes could directly and indirectly modulate different pathways, suggesting their key role during the lateral bud transition to flowering stage. Interestingly, several genes related to the flowering process appeared as over-expressed in buds from March 'OFF' branches and they could address the buds towards flower differentiation. By this approach, interesting candidate genes related to the switch from vegetative to reproductive stages were detected and analyzed. The functional analysis of these genes will provide tools for developing breeding programs to obtain olive trees characterized by more constant productivity over the years.

Automated summary

The olive tree, a typical Mediterranean crop, is important for olive and oil production, but the high tendency to bear fruits in an irregular manner leads to significant economic losses. Genes related to hormonal, sugar, and phenylpropanoid pathways play a key role in regulating the transition of olive tree lateral buds to flowering stage. Additionally, over-expressed genes related to the flowering process in buds collected from March 'OFF' branches provide insights for addressing buds towards flower differentiation.