Somatic embryogenesis (SE) in conifers: a powerful research tool and a method to capture genetic gains from the breeding programs

Somatic embryogenesis (SE) is an in vitro based clonal propagation method that can be used as a model system for research, or for multiplication of valuable seeds of commercial value or for conservation of threatened species.

In order to meet the demands on future forests for higher productivity and also for higher adaptability to climate change, it is necessary to capture the genetic gains from the breeding programs. This can only be done by large-scale clonal propagation of elite trees selected from the breeding programs.

For spruce and other conifers, somatic embryogenesis (SE) is the only method that has the potential for clonal propagation to sufficiently large numbers of elite trees for commercial planting.

The process steps of somatic embryogenesis (SE) in conifers

Cost effective SE-plant production requires automated methods. Such methods have been demonstrated on a pilot scale for Swedish forestry operations.

In the UPSC SE lab, we have an automated instrument based on the same key technology utilized in the pilot system for SE plant production (the SE Fluidics System). The instrument is a valuable tool in fundamental research projects to study embryo development. It can perform dispersion, separation/singulation, image analysis and selection of plant propagules such as somatic embryos.

The R&D SE Fluidics System is mainly used for singulation and harvest of mature somatic embryos (system overview in A). Mature somatic embryos are produced in liquid medium in a temporary immersion bioreactor system (B) where hundreds to thousands of mature embryos are produced in each bioreactor (C: top view into bioreactor), or on solid medium in a petri plate (E). After processing in the Fluidics system, singulated mature embryos are analyzed by image analysis (D) and selected based on the pre-programmed selection criteria for embryos with good chances to form a plant (F).

Our research interest is to understand and explain the different processes that regulate development of conifer embryos into early-stage plants. We utilize somatic embryogenesis as a model system to study how metabolic processes are required and regulated during embryo development. By studying the nutritional requirements of the embryo during development and the correlated active cellular processes, we have found that nitrogen utilization appears to be regulated over the course of embryo development with the earlier embryo stages benefiting from a supply of organic nitrogen such as glutamine (Dahrendorf et al. 2018). During later stages of embryo development, our results indicate the importance of desiccation tolerance and suggest key functions for different types of carbohydrates (Businge et al. 2013). Key metabolic events during shoot and root apical meristem formation are associated with morphological events during early plant formation (Dobrowolska et al. 2016).

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