Abstract
The propensity to capture and mobilize gene fragments by the highly abundant Helitron family of transposable elements likely impacts the evolution of genes in Zea mays. These elements provide a substrate for natural selection by giving birth to chimeric transcripts by intertwining exons of disparate genes. They also capture flanking exons by read-through transcription. Here, we describe the expression of selected Helitrons in different maize inbred lines. We recently reported that these Helitrons produce multiple isoforms of transcripts in inbred B73 via alternative splicing. Despite sharing high degrees of sequence similarity, the splicing profile of Helitrons differed among various maize inbred lines. The comparison of Helitron sequences identified unique polymorphisms in inbred B73, which potentially give rise to the alternatively spliced sites utilized by transcript isoforms. Some alterations in splicing, however, do not have obvious explanations. These observations not only add another level to the creation of transcript diversity by Helitrons among inbred lines but also provide novel insights into the cis-acting elements governing splice-site selection during pre-mRNA processing.
Highlights
The propensity to capture and mobilize gene fragments by the highly abundant Helitron family of transposable elements likely impacts the evolution of genes in Zea mays
Because alternative splicing and Helitrons are both viewed as potentially important forces in the processes of evolution, we examined the expression of Helitrons Hel1-331, Hel1-332, and Hel1-333 in different maize inbred lines
Total RNA from etiolated root and shoot tissues from inbred lines B73, CML277, CML322, HP301, Ki11, Mo17, Ms71, OH43, OH7B, and Tzi8 was subjected to reverse transcription (RT)-polymerase chain reaction (PCR) analysis using the same primers for each Helitron reported previously in B73 (Barbaglia et al 2012)
Summary
The propensity to capture and mobilize gene fragments by the highly abundant Helitron family of transposable elements likely impacts the evolution of genes in Zea mays. These observations add another level to the creation of transcript diversity by Helitrons among inbred lines and provide novel insights into the cis-acting elements governing splice-site selection during pre-mRNA processing. Helitron-captured gene pieces represent dead remnants of their progenitors in the majority of cases They are sometimes transcribed, giving birth to eclectic transcripts, which fuse coding regions of different genes. We recently demonstrated that alternative splicing and readthrough transcription dramatically augment the transcript diversity of Helitron-captured genes in maize (Barbaglia et al 2012) These provide a potential substrate for natural selection. These observations add another degree of complexity to the diversity of Helitron-captured genes among inbred lines for potential natural selection, and provide novel insights into the mechanism of splice site selection during pre-mRNA processing in plants
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