Progress towards the genetic transformation of Acacia crassicarpa

Acacia crassicarpa is a fast-growing tree belonging to the Leguminosae (Mimosoideae) which lives in symbiotic association with a Gram-negative bacteria, Bradyrhizobium. A. crassicarpa is native to Papua New Guinea and Australia. It is a pioneer species which has the ability to grow vigorously on poor soils of humid tropical regions. A. crassicarpa can be used for timber, pulp, fuelwood, and as a reforestation species for soil rehabilitation. Our goal is to develop a genetic transformation technique for A. crassicarpa to further introduce agronomically important traits. Regeneration of rooted plants of A. crassicarpa was obtained from callus derived from cotyledons and possibility to transfer foreign genes was investigated using both Agrobacterium tumefaciens and particle bombardment. In preliminary experiments three disarmed strains of A. tumefaciens were used: C5SC1(pGV2260), LBA4404 and EHA101. They carried in a binary vector the nptll and uidA reporter genes. Experiments were performed on 10-13 day-old decapited seedlings and inoculations were achieved either on the epicotyls or on the cotyledonary meristems. Three weeks after wounding, [bêta]-glucuronidase activity was observed in 15 to 40% of the inoculated plants. Particle bombardment was achieved on cotyledons excised from one-week-old seedlings of A. crassicarpa. Optimal conditions of shooting were determined following transient expression experiments with a plasmid containing the [bêta]-glucuronidase gene under the control of the 35S promoter. Possibility to obtain transformed tissues from the bombarded cotyledons is currently investigated. (Texte intégral