Drought and re-watering modify ethylene production and sensitivity, and are associated with coffee anthesis

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Coffee flowering requires a period of water deficit followed by rainfall to break flower bud dormancy and promote anthesis. Since drought followed by re-watering can increase shoot ethylene production, we investigated changes in root, leaf and flower bud ethylene production and expression of genes within the ethylene biosynthesis and signalling pathways and their relationship to coffee flowering. Drought decreased foliar and flower bud ethylene production without changing root ethylene production, even though all tissues likely accumulated the ethylene precursor ACC (1-aminocyclopropane-1-carboxylic acid), since ACS gene expression was maintained while ACO gene expression decreased. The ethylene receptor CaETR4-like was not differentially expressed in leaves under water deficit, but it was downregulated in roots. Re-watering restored shoot ethylene production, which seems important in promoting anthesis. 1-MCP (1- Methylcyclopropene), an ethylene action inhibitor, triggered coffee anthesis without re-watering the plants, which hitherto was considered essential to allow flowering. 1-MCP positively regulated foliar and flower bud ethylene biosynthesis genes (CaACS1-like and CaACO1-like), similar to re-watering, and downregulated CaETR4-like, suggesting that changes in ethylene levels and sensitivity are required to promote coffee anthesis. Thus, drought and re-watering-induced changes in ethylene levels and sensitivity allow coffee flowering, while the growth regulator 1-MCP can potentially regulate anthesis time and intensity.