Might exogenous circular RNAs act as protein-coding transcripts in plants?

Area of Science:

• Molecular Biology
• Plant Pathology
• RNA Biology

Background:

• Circular RNAs (circRNAs) are increasingly recognized for their regulatory roles in gene expression.
• While animal circRNAs can be translated, plant circRNAs are largely unstudied for coding potential.
• Viroids, small pathogenic plant circRNAs, have historically been considered non-coding.

Purpose of the Study:

• To investigate the coding potential of plant circRNAs, specifically viroids.
• To explore whether viroids contain translatable open reading frames (ORFs).
• To assess the biological significance of putative viroid ORFs.

Main Methods:

• Analysis of Hop stunt viroid (HSVd) and Eggplant latent viroid (ELVd) sequences for putative ORFs.
• Bioassays in host plants to evaluate the impact of ORF mutations on viroid efficiency.
• Co-sedimentation assays with polysomes to detect interaction with the translational machinery.

Main Results:

• Viroids HSVd and ELVd possess putative ORFs encoding peptides with organelle localization signals.
• Mutations in these viroid ORFs significantly reduce their biological efficiency in host plants.
• Circular forms of HSVd and ELVd were found associated with plant cell polysomes.

Conclusions:

• Plant circRNAs, exemplified by viroids, may possess non-canonical coding capacity.
• Viroids might act as translatable transcripts under specific cellular conditions.
• This challenges the traditional view of viroids as solely non-coding RNA pathogens.