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Abstract Arbuscular mycorrhizal symbiosis (AM) is a beneficial trait originating with the first land plants, which has subsequently been lost by species scattered throughout the radiation of plant diversity to the present day, including the modelArabidopsis thaliana. To explore if elements of this apparently beneficial trait are still present and could be reactivated we generatedArabidopsisplants expressing a constitutively active form ofInteracting Protein of DMI3, a key transcription factor that enables AM within the Common Symbiosis Pathway, which was lost fromArabidopsisalong with the AM host trait. We characterize the transcriptomic effect of expressingIPD3inArabidopsiswith and without exposure to the AM fungus (AMF)Rhizophagus irregularis, and compare these results to the AM modelLotus japonicusand itsipd3knockout mutantcyclops-4. Despite its long history as a non-AM species, restoringIPD3in the form of its constitutively active DNA-binding domain toArabidopsisaltered expression of specific gene networks. Surprisingly, the effect of expressingIPD3inArabidopsisand knocking it out inLotuswas strongest in plants not exposed to AMF, which is revealed to be due to changes inIPD3genotype causing a transcriptional state, which partially mimics AMF exposure in non-inoculated plants. Our results indicate that molecular connections to symbiosis machinery remain in place in this nonAM species, with implications for both basic science and the prospect of engineering this trait for agriculture. 

Abstract Circular RNAs (circRNAs) are covalently closed single‐stranded RNAs, generated through a back‐splicing process that links a downstream 5′ site to an upstream 3′ end. The only distinction in the sequence between circRNA and their linear cognate RNA is the back splice junction. Their low abundance and sequence similarity with their linear origin RNA have made the discovery and identification of circRNA challenging. We have identified almost 6000 novel circRNAs fromLotus japonicusleaf tissue using different enrichment, amplification, and sequencing methods as well as alternative bioinformatics pipelines. The different methodologies identified different pools of circRNA with little overlap. We validated circRNA identified by the different methods using reverse transcription polymerase chain reaction and characterized sequence variations using nanopore sequencing. We compared validated circRNA identified inL. japonicusto other plant species and showed conservation of high‐confidence circRNA‐expressing genes. This is the first identification ofL. japonicuscircRNA and provides a resource for further characterization of their function in gene regulation. CircRNAs identified in this study originated from genes involved in all biological functions of eukaryotic cells. The comparison of methodologies and technologies to sequence, identify, analyze, and validate circRNA from plant tissues will enable further research to characterize the function and biogenesis of circRNA inL. japonicus.