Circular RNAs and Plant Stress Responses

Circular RNAs (circRNAs) are a novel class of noncoding RNAs that have been extensively explored in the past few years. The advent of new high-throughput sequencing technologies coupled with bioinformatics tools revealed the presence of these molecules in the transcriptome of a wide range of organisms. In animals, circRNAs can modulate gene expression and act as sponges of miRNAs to inhibit their activity. It has been demonstrated that they have the potential to be diagnostic biomarkers as their expression is closely associated to human diseases, such as Alzheimer and cancer. However, in plants their function remains elusive. Recently, the role of the circRNAs in plant stress responses has been studied. During the infection of Pseudomonas syringae in kiwifruit plants, 584 circRNAs were differentially expressed in leaf samples, and a group of them could be further associated with the stage of infection. Under phosphate deficiency conditions, 27 rice circRNAs were reported to be differentially expressed. In tomato, 163 circRNAs demonstrated chilling-responsive expression, with 102 containing miRNA-binding sites and are predicted to act as miRNA sponges. Additionally, Arabidopsis seedlings presented 1583 heat-specific circRNAs, and it was also reported that heat stress could increase the quantity, length, and alternative circularization events of circRNAs. Finally, wheat seedlings under dehydration stress had 62 circRNAs differentially expressed, with 6 being predicted as miRNA sponges. Although the role of plant circRNAs during the biotic and abiotic stresses is still poorly characterised, these molecules have the potential to expand the number of targets and tools in the biotechnology field.