The banana actin 1 promoter drives near-constitutive transgene expression in vegetative tissues of banana (Musa spp.)

We have isolated a banana actin (ACT1) gene and characterised its expressio n levels, tissue-specificity and upstream regulatory sequences in banana. T he ACT1 promoter (2.2 kbp) was isolated by a combination of ligation-mediat ed polymerase chain reaction and a method for amplifying flanking sequences . A single transcriptional start site was mapped to within 215 by of the AT G, within which was located a large intron of 840 by with almost consensus monocot 5 ' and 3 ' splice recognition sites. The ACT1 gene was amplified f rom genomic DNA, and the deduced amino acid sequence showed the highest lev els of similarity to vegetatively expressed plant actins. Northern analysis indicated that the ACT1 transcript was present in all tissues examined (pe tals/sepals, stigma/stamens, leaves and roots). Expression studies in trans genic banana plants showed the ACT1 promoter drove strong reporter gene exp ression in both leaves and roots. Truncations of the ACT1 promoter suggeste d that all of the necessary regulatory elements required for strong (twofol d greater than CaMV 35S) near-constitutive expression were located within 1 .2 kbp of the ACT1 ATG.