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

Abstract.

We have isolated a banana actin (ACT1) gene and characterised its expression levels, tissue-specificity and upstream regulatory sequences in banana. The ACT1 promoter (2.2 kbp) was isolated by a combination of ligation-mediated polymerase chain reaction and a method for amplifying flanking sequences. A single transcriptional start site was mapped to within 215 bp of the ATG, within which was located a large intron of 840 bp with almost consensus monocot 5′ and 3′ splice recognition sites. The ACT1 gene was amplified from genomic DNA, and the deduced amino acid sequence showed the highest levels of similarity to vegetatively expressed plant actins. Northern analysis indicated that the ACT1 transcript was present in all tissues examined (petals/sepals, stigma/stamens, leaves and roots). Expression studies in transgenic banana plants showed the ACT1 promoter drove strong reporter gene expression in both leaves and roots. Truncations of the ACT1 promoter suggested that all of the necessary regulatory elements required for strong (twofold greater than CaMV 35S) near-constitutive expression were located within 1.2 kbp of the ACT1 ATG.