Roles of the first intron on the expression of Arabidopsis (Arabidopsis thaliana) genes for actin and actin-binding proteins

We have recently reported that intron is required for strong and constitutive expression of two actin-binding proteins (ABPs), actin-depolymerizing factor (ADF) and profilin in vegetative tissues. To examine whether the expression of their target gene, actin, is also regulated by the introns, we examined the role of the first intron on the expression of the ACT2 gene, which encodes vegetative actin, using transgenic plants and a transient expression system. Transgenic plants carrying the ACT2 promoter-GUS with its first intron showed strong expression throughout the vegetative tissues, and the intron was necessary for expression in the shoot apical meristem region and root tips. Along with changes in expression pattern, the intron also increased GUS expression about 13-fold. However, this enhancement was not observed when the intron was moved upstream of the ACT2 promoter or the minimal promoter, suggesting that the intron is not a transcriptional enhancer. To further examine the role of the intron in the expression of actin and ABP genes, introns of actin, ADF, and profilin genes were exchanged. Introns of vegetative profilin and the ADF genes significantly enhanced gene expression under the control of heterologous promoters. Together with the role of the first intron of the ACT2 gene, these results suggest that the expression of actin and ABPs is regulated by intron-mediated enhancement.