Abstract
Research into somatic embryogenesis in coffee has enabled the development of effective protocols, originally for clonal multiplication and later for genetic transformation in the two cultivated species, Coffea arabica and Coffea canephora, making these species a veritable model for woody plants. Most of the traditional obstacles involved in clonal multiplication such as obtaining embryogenic tissues, converting embryos into plants and the risks of losing genetic conformity have been resolved. Scaling up of somatic embryogenesis was achieved by different groups using temporary immersion bioreactors, which enabled mass production of pre-germinated embryos, and through the development of effective acclimatisation and nursery hardening procedures applied on a large scale. This technology is currently being used to speed up breeding programmes and for the large-scale dissemination of heterozygous genotypes or mutants of great agronomic interest (arabica F1 hybrids, Robusta clones). Several OMICs studies on coffee somatic embryogenesis have improved our understanding of the underlying key mechanisms. Mastery of coffee somatic embryogenesis has facilitated the development of methods for Agrobacterium tumefaciens-mediated genetic transformation and enabled the functional analysis of genes involved in coffee quality or the adaptation of coffee plants to environmental stresses, such as drought. Based on similar protocols, successful genome editing of C. canephora was reported in 2018. Here we review the state of the art in these three areas of application of somatic embryogenesis in coffee tree, that is clonal mass propagation, genetic transformation and genome editing, describe the difficulties encountered, the role played by somatic embryogenesis in these technological developments, and its future outlook.