Homeologous Genes Involved in Mannitol Synthesis Reveal Unequal Contributions in Responses to Abiotic Stress in Coffea arabica

Coffea arabica is an allotetraploid originating from a natural hybridization between C. canephora and C. eugenioides, and it accounts for 75% of the world’s coffee production. Abiotic stresses, such as extreme temperatures, salinity, and drought, limit worldwide commercial coffee production. The accumulation of compatible solutes, such as mannitol, is known to be involved in abiotic stress tolerance in higher plants. The aim of this study was to investigate the transcriptional responses of genes involved in mannitol biosynthesis and catabolism in C. arabica leaves under water deficit, salt stress and high temperature. Mannitol concentration was significantly increased in leaves of plants under drought and salinity but reduced by heat stress. Fructose content followed the level of mannitol only in heat-stressed plants, suggesting the partitioning of the former into other metabolites during drought and salt stress conditions. Transcripts of the key enzymes involved in mannitol biosynthesis, CaM6PR, CaPMI and CaMTD, were modulated in distinct ways depending on the abiotic stress. Our data suggest that changes in mannitol accumulation during drought and salt stress in leaves of C. arabica are due, at least in part, to the increased expression of the key genes involved in mannitol biosynthesis. In addition, the homeologs of the C. canephora subgenome did not present the same pattern of overall transcriptional response, indicating differential regulation of these genes by the same stimulus. Finally, this study adds new information on the differential expression of C. arabica homeologous genes under adverse environmental conditions.