The Putative Smallest Introns in the Arabidopsis Genome

Most eukaryotic genes contain introns, which are noncoding sequences that are removed during premRNA processing. Introns are usually preserved across evolutionary time. However, the sizes of introns vary greatly. In Arabidopsis, some introns are longer than 10 kilo base pairs (bp) and others are predicted to be shorter than 10 bp. To identify the shortest intron in the genome, we analyzed the predicted introns in annotated version 10 of the Arabidopsis thaliana genome and found 103 predicted introns that are 30 bp or shorter, which make up only 0.08% of all introns in the genome. However, our own bioinformatics and experimental analyses found no evidence for the existence of these predicted introns. The predicted introns of 30-39 bp, 40-49 bp, and 50-59 bp in length are also rare and constitute only 0.07%, 0.2%, and 0.28% of all introns in the genome, respectively. An analysis of 30 predicted introns 31-59 bp long verified two in this range, both of which were 59 bp long. Thus, this study suggests that there is a limit to how small introns in A. thaliana can be, which is useful for the understanding of the evolution and processing of small introns in plants in general.