Caracterização de microRNAs potencialmente responsivos ao fitormônio etileno em cafeeiro

Abstract

Coffee is the second largest commodity in Brazil, with great importance for the economy. Several cultivars have already been developed, but asynchronous flowering is still a problem in this crop. This asynchrony causes uneven maturation of the fruits, leading to losses in the quality of the final product and in profitability. It is known that a period of water deficit followed by rehydration stimulates the anthesis of buds that are able to respond to this stimulus, which means that this strategy is constantly adopted to concentrate the flowering. In some species it has been observed that water stress followed by rehydration increases ethylene levels. This finding led to the hypothesis of the involvement of ethylene in the promotion of anthesis in coffee. The application of 1-MCP (ethylene action inhibitor) promoted anthesis in coffee in field condition and increased the expression of genes involved in ethylene biosynthesis. microRNAs are involved in several stages of plant development, including flowering, and some recent studies report that they are involved in ethylene signaling pathways. In order to explore how microRNAs may be involved in the flowering process of coffee and its relation with ethylene, the objective of this work was to evaluate the effects of 1-MCP application on the expression of microRNAs potentially responsive to this hormone in coffee flower buds, as well as the characterization of possible targets for these molecules, in plants under different water conditions. miR396, miR156, miR319 and miR172 were chosen for the analysis of gene expression by stem-loop RT-PCR, target prediction and analysis of gene ontology terms. In plants under water stress, the four microRNAs were responsive to the application of 1-MCP. miR396a-5p and miR156f-3p were repressed and miR319-2-3p and miR172d-1-3p were induced. For the completely re-irrigated and constantly irrigated plants there was no difference in expression for the four microRNAs between the treatments probably because 1-MCP had the same effect as the irrigation in the anthesis of the coffee tree. The analysis of the gene ontology terms for the predicted targets for each microRNA indicates that they may be involved in the signaling pathways, including ethylene signaling.