Transgenic Spartina alterniflora for phytoremediation

Perennial monoculture forming grasses are very important natural remediators of pollutants. Their genetic improvement is an important task because introduction of key transgenes can dramatically improve their remediation potential. Transfer of key genes for mercury phytoremediation into the salt marsh cordgrass (Spartina alterniflora) is reported here. S. alterniflora plays an important role in the salt marsh by cycling of␣elements, both nutrients and pollutants, protects the coastline from erosion, is a keystone species in the␣salt marsh supporting a large food web, which in turn supports a significant segment of economy, including tourism, has an impact on cloud formation and consequently on global weather, and is thus an ecologically important species relevant for our life-support systems. Embryogenic callus of S. alterniflora was co-inoculated with a pair of Agrobacterium strains LBA4404 carrying the organomercurial lyase (merB) and mercuric reductase (merA) genes, respectively, in order to co-introduce both the merA and the merB genes. Seven stable geneticin resistant lines were recovered. The presence of merA and merB genes was verified by PCR and Southern blotting. All but one transgenic lines contained both the merA and the merB sequences proving that co-introduction into Spartina of two genes from separate Agrobacterium strains is feasible and frequent, although the overall frequency of transformation is low. Northern blotting showed differences in relative expression of the two transgenes among individual transformants. The steady-state RNA levels appeared to correlate with the phenotype. Line #7 showed the highest resistance to HgCl₂ (up to 500 μM), whereas line #3 was the most resistant to phenylmercuric acetate (PMA). Wild-type (WT) callus is sensitive to PMA at 50 μM and to HgCl₂ at 225 μM.