Canadian Forest Service Publications

Potential link between biotic defense activation and recalcitrance to induction of somatic embryogenesis in shoot primordia from adult trees of white spruce (Picea glauca). 2013. Rutledge, R.G.; Stewart, D.; Caron, S.; Overton, C.; Boyle, B.; MacKay, J.; Klimaszewska, K. BMC Plant Biol. 13:116.

Year: 2013

Issued by: Laurentian Forestry Centre

Catalog ID: 35163

Language: English

Availability: PDF (request by e-mail)

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Background: Among the many commercial opportunities afforded by somatic embryogenesis (SE), it is the ability to clonally propagate individual plants with rare or elite traits that has some of the most significant implications. This is particularly true for many long-lived species, such as conifers, but whose long generation times pose substantive challenges, including increased recalcitrance for SE as plants age. Identification of a clonal line of somatic embryo-derived trees whose shoot primordia have remained responsive to SE induction for over a decade, provided a unique opportunity to examine the molecular aspects underpinning SE within shoot tissues of adult white spruce trees.

Results: Microarray analysis was used to conduct transcriptome-wide expression profiling of shoot explants taken from this responsive genotype following one week of SE induction, which when compared with that of a nonresponsive genotype, led to the identification of four of the most differentially expressed genes within each genotype. Using absolute qPCR to expand the analysis to three weeks of induction revealed that differential expression of all eight candidate genes was maintained to the end of the induction treatment, albeit to differing degrees. Most striking was that both the magnitude and duration of candidate gene expression within the nonresponsive genotype was indicative of an intense physiological response. Examining their putative identities further revealed that all four encoded for proteins with similarity to angiosperm proteins known to play prominent roles in biotic defense, and that their high-level induction over an extended period is consistent with activation of a biotic defense response. In contrast, the more temperate response within the responsive genotype, including induction of a conifer-specific dehydrin, is more consistent with elicitation of an adaptive stress response.

Conclusions: While additional evidence is required to definitively establish an association between SE responsiveness and a specific physiological response, these results suggest that biotic defense activation may be antagonistic, likely related to the massive transcriptional and metabolic reprogramming that it elicits. A major issue for future work will be to determine how and if suppressing biotic defense activation could be used to promote a physiological state more conducive to SE induction.

Plain Language Summary

Somatic embryogenesis is a plant cloning process that takes place in the laboratory. It can be used to reproduce conifer trees with desirable characteristics (size, wood quality, etc.), and make thousands of copies.

Up until very recently, this process could only be applied to seedlings and young tree shoots. This study made it possible, for the first time, to induce somatic embryogenesis from shoots of a mature white spruce.

The researchers found that the cells of mature trees responded to somatic embryogenesis treatment in one of two ways: by fighting or adapting. The somatic embryogenesis treatment causes significant stress to the cells of the tree in question. When they fight against this stress, they either die or survive by adapting to these new conditions.

This work has made it possible to identify several chemical compounds that could play a role in the fight-or-adapt response of these tree cells during somatic embryogenesis.