Large Introns of 5 to 10 Kilo Base Pairs Can Be Spliced out in Arabidopsis.

Most of the eukaryotic genes contain introns, which are removed from the pre-RNA during RNA processing. In contrast to the introns in animals, which are usually several kilo base pairs (kb), those in plants generally are very small, which are mostly from dozens of base pairs (bp) to a few hundred bp. According to annotation version 10.0 of the genome of Arabidopsis thaliana, there are 127,854 introns in the nuclear genes; 99.23% of them are less than 1 kb, and only 16 introns are annotated to be larger than 5 kb, which are extremely large introns (ELI) in Arabidopsis. To learn whether these introns are true introns or not and how large introns could be in Arabidopsis, RT-PCR analysis of genes containing these ELIs were carried out. The results indicated that some of these putative introns are indeed ELIs. These ELIs are mainly composed of transposons or transposable elements (TE), excepting one, whose counterparts are also very long in diverse plant species. Thus, this study confirms the existence of introns larger than 5 kb or even 10 kb in Arabidopsis.