An efficient method for hairy root transformation and transgenic plant regeneration of Melia azedarach

Rhizobium rhizogenes -mediated hairy root induction and transformation have been developed and applied in various plant species. In this study, an efficient procedure for hairy root induction was established for Melia azedarach , an economically important woody plant worldwide. The highest hairy root induction efficacy (91.8%) was achieved using optimal transformation parameters including R. rhizogenes strain ATCC 15834 at density of OD 650 = 0.6, hypocotyl segments as initial explants, and 3 days of co-cultivation. Different hairy root phenotypes including hairy roots with limited branching (type 1), green compact callus formation (type 2), shoot induction (type 3), and white fragile callus formation (type 4) were found as results from the presences of T L and T R -DNA in hairy root lines. Among them, the abundance of the T L -DNA insertion was confirmed in most of the tested hairy roots. The two hairy root phenotypes (type 1 and type 2) showed potential to induce whole regenerated plants at the average rates from 29.13 to 76.40%. The established procedure was successfully used to validate the activity of the GUS reporter gene construct in hairy roots and directly regenerate transgenic shoots. This is the first report in development of the hairy root induction and transformation system for Melia azedarach and provides a potential approach for further fundamental and applied research in this woody plant.