Establishment of an efficient protocol for regeneration and genetic transformation is required in
banana for the incorporation of useful traits. Therefore an efficient
method has been developed for somatic embryogenesis, plant regeneration and transformation of Cavendish
banana cultivar Robusta (AAA). Embryogenic cell suspension culture
(ECS) was established using immature male flowers. Percentage appearance of embryogenic callus and
distinct globular embryos was 10.3 and 11.1, respectively. ECS obtained was cocultivated under different cocultivation
conditions with Agrobacterium tumefaciens strain EHA105 harboring
pCAMBIA 1301 plant expression vector. Up to 30 transgenic plants/50 mg settled cell volume
(SCV) was obtained with cocultivation in semisolid medium whereas no transgenics could be obtained with parallel
experiments carried out in liquid medium. Histochemical GUS assay in different tissues of putatively transformed
plants demonstrated expression of uidA gene. Among the putatively transformed plants obtained, a set of 4 were
confirmed by PCR analysis and stable integration of the transgene by Southern analysis. GUS specific activity
measured by a MUG (4-methylumbelliferyl-b-D-glucuronide)
based flourometric assay revealed increase in transient GUS expression in semisolid as well as liquid cocultivation
with centrifugation. This is the first report showing somatic embryogenesis and
Agrobacterium tumefaciens mediated transformation using embryogenic cell
suspension cultures in an important Cavendish banana cultivar Robusta. The
present protocol will make possible agronomic improvement of this important
commercially grown cultivar by introduction of disease resistance characteristics
and antisense-mediated delayed fruit ripening strategies. Further, it
will also assist in functional characterization of new gene or promoter elements isolated from this or
other cultivars of banana.
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