Efficient production of Agrobacterium rhizogenes-transformed roots and composite plants in peanut (Arachis hypogaea L.)

Recalcitrance of most large-seeded legumes, such as peanut, to regeneration and genetic transformation has hampered studies on gene function and efforts for genetic improvement. Agrobacterium rhizogenes-mediated transformation provides a system for rapid and efficient transformation of plant tissues. In this study, embryonic axes along with cotyledons of peanut were injected with a suspension culture of A. rhizogenes using microliter syringes. The influence of several factors such as plant genotype, A. rhizogenes culture stage, co-culture period of A. rhizogenes, and acetosyringone concentration in the co-cultivation medium have been evaluated. It is found that A. rhizogenes-mediated transformation of peanut is genotype-independent. Up to 61% transformation was recorded when embryonic axes were co-cultivated with 5 × 10 A. rhizogenes cells from logarithmic phase for 2 days on co-culture medium containing 50 μmol l acetosyringone. Composite plants with transgenic roots were harvested after 45 days of treatment. Furthermore, this method was applied to assess the insecticidal activity of a synthetic cry8Ea1 gene against Holotrichia parallela in transgenic roots of peanut