A single-nucleotide exon found in Arabidopsis

Area of Science:

• Molecular Biology
• Genetics
• Plant Science

Background:

• Introns in eukaryotic gene-coding regions are evolutionarily enigmatic.
• Exonic sequences, in addition to intronic sequences, can influence intron splicing.
• Previously, the smallest known constitutively spliced exon was 6 nucleotides, and alternatively spliced exons were 3 nucleotides.

Purpose of the Study:

• To investigate the minimum size of functional exons in plant genes.
• To report the discovery of a single-nucleotide exon in Arabidopsis thaliana.
• To assess the splicing efficiency of this minimal exon in vivo.

Main Methods:

• Identification of a single-nucleotide exon in the Anaphase Promoting Complex subunit 11 (APC11) gene of Arabidopsis thaliana.
• In vivo transcription and translation assays using APC11-Green Fluorescence Protein (GFP) fusion constructs.
• Analysis of splicing effectiveness in both Arabidopsis and rice.

Main Results:

• A constitutive single-nucleotide exon was identified in the APC11 gene of Arabidopsis thaliana.
• In vivo assays confirmed effective intron splicing surrounding this single-nucleotide exon in both Arabidopsis and rice.
• This represents the smallest known constitutive exon in any organism.

Conclusions:

• The existence of a single-nucleotide exon challenges current models of exon definition and splicing.
• Plant genomes may contain numerous unannotated minimal exons.
• Future genome annotations should consider the possibility of extremely small exons for accurate gene prediction.