Optimization of hairy root induction and producing high vindoline and catharanthine clones in Catharanthus roseus through Transformation by Agrobacterium rhizogenes

 Hairy roots induced by inoculation with Agrobacterium rhizogenes are suitable for the production and accumulation of plant secondary metabolites. Genetically modified hairy roots produce valuable secondary metabolites to a greater amount and with more genetic stability than cell suspension cultures and normal roots. Catharanthus roseus is one of the most important medicinal plants that produces valuable secondary metabolites such as indole alkaloids. The purpose of this research was to investigate the effect of factors influencing the induction of hairy roots and to investigate the amount of production of secondary metabolites (vindoline and catharanthine) in the hairy roots produced by inoculation of C. roseus plant with A. rhizogenes.

 In order to produce sterile C. roseus seedlings and to prepare explants, seeds cultured on MS culture medium. The effect of the type of culture medium (MS, 1/2 MS and B5), the type of explant (leaf and stem), the type of bacterial strain (A4, 1132 and 2656) and the type of plant genotype (white and red) on the amount of hairy root induction in a completely randomized design was investigated. Extraction of samples was done using methanol solvent, then the amount of indole alkaloids was calculated using HPLC method and standard curve. The nature of transgenic hairy roots was confirmed after DNA extraction from different samples using PCR method with specific primers (rolB and virD).

 According to the results, the most efficient strain in transferring T-DNA to the explants and the appearance of hairy roots was related to A4 strain (53.8%). 1/2 MS culture medium with 77.69% of root induction was the best medium combination for the appearance of hairy roots. Also, white genotype (62% rooting) and leaf explant (77% rooting) were identified as the best genotype and explant for the production of hairy roots. After the specific amplification of the rolB gene and the lack of amplification of the virD gene in the PCR reaction in the samples, the molecular confirmation of the transgenic nature of the hairy root clones was done. Based on the results of HPLC experiment, the average amount of vindoline and catharanthine in hairy roots (0.24 and 0.615 mg/g dry weight) is higher than aerial parts (0.106 and 0.488 mg/g dry weight) and normal root (0.021 and 0.013 mg/g dry weight). The amount of these alkaloids in the aerial parts was higher than in the normal roots of the plant.

 The production of hairy roots in response to the inoculation of plant explants with A. rhizogenes is influenced by various factors such as the type of explant, the genotype of the plant, the strain of bacteria and the composition of culture medium. These factors must be optimized to establish effective hairy root cultur in a plant. It seems that with the introduction of rol genes from bacteria to the plant genome (hairy root) and as a result of the change in the amount of endogenous hormone production and the response of the plant cell to the entry of bacterial genes, the amount and profile of the production of the secondary metabolites of the plant will change. As a result, by selecting clones with increased production of medicinally important alkaloids and optimizing the conditions of large scale production of secondary metabolites in bioreactors, we can move towards the commercial production of these compounds through cell and plant tissue culture.