Somatic embryogenesis is a promising vegetative propagation technology developed in France in the frame of a collaboration between FCBA and INRA of Orléans. A recent study (collaboration FCBA/University of Málaga, Spain) reported that arginine metabolism is dysregulated in maritime pine somatic embryos as compared with reference zygotic embryos from seeds. Arginine is an amino acid with high nitrogen content found in storage proteins. Dysfunction in both biosynthesis and metabolic utilization (catabolism) of arginine could explain the low initial vigor of somatic seedling in field tests established by FCBA since 1999. Such a knowledge will help to refine biotechnological procedures for clonal propagation of maritime pine via somatic embryogenesis, especially through the refinement of nitrogen nutrition during embryo development.
FCBA and INRA are refining for more than 20 years a powerful method for vegetative propagation of maritime pine through somatic embryogenesis, a process mimicking embryonal development in seeds but without sexual reproduction. Multiple applications are expected in genetic breeding, from sustainable management of genetic resources to more efficient selection and deployment of elite varieties in plantation forestry.
Field test managed by FCBA since 1999 showed that somatic seedlings have low initial vigor compared to reference seedling from seeds. Tree growth rate is however restored to levels observed in controls after a few years suggesting that the intrinsic quality of somatic embryo is somewhat different from that of zygotic embryos from seeds. Molecular analyses performed by INRA in the frame of the PhD thesis of Morel (2014) demonstrated that under our current experimental conditions, cotyledonary SEs did not reach a level of maturity equivalent to that of cotyledonary ZEs from dried seeds, especially considering storage proteins.
A long-lasting scientific collaboration was established between FCBA and a team from the University of Málaga (Spain) with high expertise in tree nitrogen metabolism (Pr. F. Cánovas and C. Avila). One important objective of this partnership is to study molecular aspects of somatic embryo quality in maritime pine related with nitrogen metabolism. Mobilization of nitrogen-rich proteins is indeed essential for the germination and production of vigorous somatic seedlings. XYLOBIOTECH was in charge of supplying different embryo developmental stages in a recent comparative study of somatic and zygotic embryos (Llebres et al. 2017, in press). This report showed that arginine metabolism is dysregulated in somatic embryos (simultaneous biosynthesis and degradation of arginine) and could explain the lower accumulation of storage proteins observed during the late stages of somatic embryogenesis. By contrast, arginine catabolism is only observed during the last stages of maturation and germination of zygotic embryos. These results suggested an overlap between late embryogenesis and precocious germination which is an unfavorable process for subsequent somatic plant development. New protocols would be hopefully designed for refinement of somatic embryo quality based in particular on improved nitrogen nutrition during embryo development.
Collaboration FCBA/University of Málaga, Spain
This study was partially supported by the French Ministry of Agriculture (DGAL, N°2014-352, QuaSeGraine project).
Link to the publication of Llebres et al. (2017)