Alternative processing of the maize Ac transcript in Arabidopsis

Abstract

The successful application of the maize transposable element system Ac/Ds as a genome mutagen in heterologous plant species has recently proved the versatility and power of this technique in plant molecular biology. However, the frequency of Ac/Ds transposition is considerably lower in Arabidopsis thaliana than in most other dicot plant species that have been studied. Since previous research has established that transcripts derived from monocot genes can be alternatively processed in dicot plants, we have investigated both the efficiency of intron splicing and polyadenylation of the maize Ac transposase pre-mRNA in Arabidopsis thaliana, Nicotiana tabacum, Nicotiana plumbaginifolia and Zea mays. In this paper, we demonstrate that intron 4 is alternatively spliced within Arabidopsis, using cryptic 5' and 3'splice sites within the intron sequence, leading to a heterogeneous population of full length of transposase transcript. Furthermore, analysis of transposase transcript polyadenylation revealed that at least four alternative poly(A) sites were utilized between introns 2 and 3, resulting in truncated transposase transcripts. Finally, by Northern blotting, we established that the truncated transposase transcript was the most abundant form of transposase message in Arabidopsis. In contrast to these findings, the alternative splicing and premature polyadenylation of Ac message in Arabidopsis was unparalleled in the other species examined. We suggest that the poor frequency of transposition of Ac in Arabidopsis may be in part due to the low quantity of correctly processed transposase transcript available in this species.