Marshall, C. M. | bioRxiv Science

bioRxiv2023

Lariat debranching by RNA DEBRANCHING ENZYME 1 depends on SICKLE in Arabidopsis thaliana

Spliceosome mediated intron removal from precursor mRNAs (pre-mRNAs) generates circular RNAs called intron lariats. RNA DEBRANCHING ENZYME 1 (DBR1) ribonucleases linearize, or debranch, intron lariats to allow their degradation. DBR1 genes occur across eukaryotes and are essential in animals and plants. High levels of intron lariats in the weak Arabidopsis thaliana dbr1-2 allele inhibits primary microRNA (pri-miRNA) processing, disrupting miRNA production and miRNA-regulated growth and development. Arabidopsis sickle (sic) mutants alter pri-miRNA processing and pre-mRNA splicing. This study demonstrates sic mutants accumulate intron lariats matching those in weak dbr alleles. The strong sic-1 and weak dbr1-3 alleles together cause synthetic lethality, while weak sic-3 with dbr1-3 has intron lariat accumulation like sic-3. Further, sic-3, dbr1-3, and sic-3 dbr1-3 similarly alter circadian rhythms and growth of roots and rosettes. The conserved MPLKIP amino acid motif in SIC mediates physical interaction with DBR1 in vitro and is required for intron lariat debranching in vivo. Thus, MPLKIP containing proteins, like SIC and human TTDN1, act with cognate DBR1 proteins to maintain RNA homeostasis critical for growth and development.

molecular biology↗

bioRxiv2022

The circadian clock controls temporal and spatial patterns of floral development in sunflower

Biological rhythms are ubiquitous. They can be generated by circadian oscillators, which produce daily rhythms in physiology and behavior, as well as by developmental oscillators such as the segmentation clock, which produces modular developmental units in a periodic fashion. Here, we show that the circadian clock controls the timing of late-stage floret development, or anthesis, in domesticated sunflower. In these plants, what appears to be a single inflorescence consists of up to thousands of individual florets tightly packed onto a capitulum disk. While early floret development occurs continuously across capitula to generate iconic spiral phyllotaxy, during anthesis floret development occurs in discrete ring-like pseudowhorls with up to hundreds of florets undergoing simultaneous maturation. We demonstrate circadian regulation of floral organ growth and show that the effects of light on this process are time-of-day dependent. Disruption of circadian rhythms in floral organ development causes loss of pseudowhorl formation. Thus, we show that the sunflower circadian clock acts in concert with environmental response pathways to tightly synchronize the anthesis of hundreds of florets each day, generating spatial patterns on the developing capitulum disk. This coordinated mass release of floral rewards at predictable times of day likely promotes pollinator visits and plant reproductive success.

plant biology↗