Molecular mechanisms in the first step of ABA-mediated response to drought in Coffea canephora clones

Global climate changes are becoming more unpredictable and abiotic stress, such as drought and high temperatures, are key factors that affect coffee plant development and production. Although the strategies for drought adaptation in perennial plants are complex, there is genetic variability within the Coffea genus that could be used to increase tolerance. Drought tolerant clones of Coffea canephora have been characterized as vigorous plants with high productivity throughout years under water deficit. Recently, novel intracellular ABA receptors (PYL/RCARs) involved in sensing and signaling of this hormone were identified. A mechanism of ABA transduction was proposed, involving PYR/PYL/RCARs receptors interacting with PP2Cs phosphatases and SnRK2 protein kinases. The goal of this study was to identify and characterize orthologous genes of this tripartite system in C.canephora. For this purpose, protein sequences from Arabidopsis, citrus, rice, grape, and tomato were chosen as query to search orthologous genes in sequence databases. This approach allowed the identification and characterization of 24 candidate genes (9 PYL/RCAR, 6 PP2Cs and 9 SnRK2s) in C. canephora genome. The protein domains identified in the predicted coffee sequences enabled to characterize these genes as family's members of receptors (PYR/PYL/ RCAR), phosphatases (PP2Cs) or kinases (SnRK2) of ABA response pathway. Phylogenetic analysis allowed the classification of coffee-polypeptide sequences between subclasses and subfamilies. The gene structures of these three gene families were functionally annotated in Coffee Genome Hub (http://coffee-genome.org/). Tissue (leaf, seed, root and floral organ) differential expression was verified through in silico analyses. Regarding drought conditions, data from root transcriptome showed contrasting gene expression for those genes between the tolerant (Cc14, Cc73 and Cc120) and susceptible(Cc22)clones of C. canephora. By comparing gene expression profiles of only drought tolerant(Cc14, Cc73 and Cc120) clones, differential responses were observed suggesting the existence of multiple biological mechanisms for drought tolerance in coffee. All those evidences will help to identify the genetic determinism of drought tolerance essential to obtain molecular markers that could be used in coffee breeding programs. (Résumé d'auteur