Camellia sinensis var. sinensis is widely grown for tea beverages that possess significant health promoting effects. Studies on tea plant genetics and breeding are hindered due to its recalcitrance to Agrobacterium-mediated genetic transformation. Among the possible reasons, oxidation of phenolics released from explant tissues and bactericidal effects of tea polyphenols during the process of transformation play a role in the plant recalcitrance. The aim of the present study was to alleviate the harmful effects of phenolic compounds using in-planta transformation. Two-month old seedlings of tea cultivar “Nong Kangzao” were infected at the hypocotyl with wild type Agrobacterium rhizogenes and maintained in an environment of high humidity. 88.3% of infected plants developed hairy roots at the wounded site after 2 months of infection. Our data indicated that transgenic hairy root induction of tea can be achieved using A. rhizogenes following the optimized protocol. With this method, composite tea plants containing wild-type shoots with transgenic roots can be generated for “in root” gene functional characterization and root-shoot interaction studies. Moreover, this method can be applied to improve the root system of composite tea plants for a better resistance to abiotic and biotic stresses.

Tea (Camellia sinensis L.) is recalcitrant to Agrobacterium-mediated genetic transformation largely due to the bactericidal effects of tea polyphenols and phenolics oxidation induced by necrosis of explant tissue over the process of transformation. In this study, different antioxidants/adsorbents were added as supplements to the co-cultivation and post co-cultivation media to overcome these problems for the transformation improvement. Tea-cotyledon-derived calli were used as explants and Agrobacterium rhizognes strain ATCC 15834 was used as a mediator. Results showed that Agrobacterium growth, virulence (vir) gene expression and browning of explant tissue were greatly influenced by different supplements. Murashige and Skoog (MS) basal salts medium supplemented with 30 g·L⁻¹ sucrose, 0.1 g·L⁻¹ l-glutamine and 5 g·L⁻¹ polyvinylpolypyrrolidone (PVPP) as co-cultivation and post co-cultivation media could maintain these parameters better that ultimately led to significant improvement of hairy root generation efficiency compared to that in the control (MS + 30 g·L⁻¹ sucrose). Additionally, the reporter genes β-glucuronidase (gusA) and cyan fluorescent protein (cfp) were also stably expressed in the transgenic hairy roots. Our study would be helpful in establishing a feasible approach for tea biological studies and genetic improvement of tea varieties.