Establishment of a direct somatic embryogenesis regeneration system using immature cotyledon explants in Camellia sinensis cv. Shuchazao

Tea is one of the most popular non-alcoholic beverages, while tea plant is also an important cash crop in the world. Somatic embryogenesis (SE) is a powerful tool for producing large scale vegetative propagation, but the unestablished SE regeneration system greatly impedes the mass production of tea seedlings, and thereby affecting the development of tea industry. In this study, we established a high-efficiency direct SE system in tea including somatic embryo initiation, maturation and germination. Somatic embryo initiation was affected by tea cultivars, explant age and plant growth regulator. Cotyledons of tea seeds at 270 days after flowering had the highest globular embryos induction efficiency as explant. Somatic embryos were induced well in embryos initiation medium adding 1 mg/L NAA and 0.5 mg/L 6-BA. The optimum induction rate from globular embryos to cotyledonary embryos was 12.62 ± 1.57%, when the globular embryos was transferred to the hormone-free medium supplemented with 2 g/L activated carbon. Mature embryos germinated to produce plantlet on MS medium with 1 mg/L 6-BA and 0.1 mg/L NAA with a generation frequency of 20.2 ± 0.1%. In addition, six SE-related genes were identified, and the expression level of these genes during the SE of tea were analyzed by quantitative real-time RT-PCR (qRT-PCR). These genes showed higher expression level in the initiation embryo stage than maturated embryo stage, which deduced that these genes are crucial during the initiation of SE in tea. Taken together, the establishment of a direct SE regeneration system for tea plant would confer to large-scale propagation and genetic improvement of tea plant as well as studies about SE-related genes would lay the foundation for further clarifying the molecular mechanism of SE in tea plant.