Cytoplasmic HYL1 modulates miRNA-mediated translational repression

MicroRNAs (miRNAs) control various biological processes by repressing target mRNAs. In plants, miRNAs mediate target gene repression via both mRNA cleavage and translational repression. However, the mechanism underlying this translational repression is poorly understood. Here, we found that Arabidopsis thaliana HYPONASTIC LEAVES1 (HYL1), a core component of the miRNA processing machinery, regulates miRNA-mediated mRNA translation but not miRNA biogenesis when it localized in the cytoplasm. Cytoplasmic HYL1 localizes to the endoplasmic reticulum and associates with ARGONAUTE1 (AGO1) and ALTERED MERISTEM PROGRAM1 (AMP1). In the cytoplasm, HYL1 monitors the distribution of AGO1 onto polysomes, binds to the mRNAs of target genes, represses their translation, and partially rescues the phenotype of the hyl1 null mutant. This study uncovered another function of HYL1 and provides insight into the mechanism of plant gene regulation.

Testing the inferred transcription rates of a dynamic, gene network model in absolute units

The circadian clock coordinates plant physiology and development. Mathematical clock models have provided a rigorous framework to understand how the observed rhythms emerge from disparate, molecular processes. However, models of the plant clock have largely been built and tested against RNA timeseries data in arbitrary, relative units. This limits model transferability, refinement from biochemical data and applications in synthetic biology. Here, we incorporate absolute mass units into a detailed, gene circuit model of the clock in Arabidopsis thaliana. We re-interpret the established P2011 model, highlighting a transcriptional activator that overlaps the function of REVEILLE 8/LHY-CCA1-LIKE 5, and refactor dynamic equations for the Evening Complex. The U2020 model incorporates the repressive regulation of PRR genes, a key feature of the most detailed clock model F2014, without greatly increasing model complexity. We tested the experimental error distributions of qRT-PCR data calibrated for units of RNA transcripts/cell and of circadian period estimates, in order to link the models to data more appropriately. U2019 and U2020 models were constrained using these data types, recreating previously-described circadian behaviours with RNA metabolic processes in absolute units. To test their inferred rates, we estimated a distribution of observed, transcriptome-wide transcription rates (Plant Empirical Transcription Rates, PETR) in units of transcripts/cell/hour. The PETR distribution and the equivalent degradation rates indicated that the models' predicted rates are biologically plausible, with individual exceptions. In addition to updated, explanatory models of the plant clock, this validation process represents an advance in biochemical realism for models of plant gene regulation.

Biogenesis and functional RNAi in fruit trees.

In plants, genome expression is linked to the transcribed mRNAs that are synthesized by RNA polymerase. Following its move to the cytoplasm, the generated mRNA is briefly translated to the encoded protein. If transcription and translation are dependent on the family of RNA polymerase, these two phenomena could be interfered with through the process designated as gene regulation. Thus, large molecules of RNA (single-stranded or double-stranded) consequently sliced into small molecules produce nascent small interfering RNA ranging from 21 to 27 nucleotides. This chapter revisits the biogenesis of these two types of RNAi, miRNA and siRNA, and notably their involvement in plant gene regulation. Following their sequential transcription and their specific involvement, we will consider the sources and roles of RNA interference in plants and we will look at their detection in fruit crops. We discuss their applications and the risk assessment studies in fruit crops.

Biogenesis and functional RNAi in fruit trees.

In plants, genome expression is linked to the transcribed mRNAs that are synthesized by RNA polymerase. Following its move to the cytoplasm, the generated mRNA is briefly translated to the encoded protein. If transcription and translation are dependent on the family of RNA polymerase, these two phenomena could be interfered with through the process designated as gene regulation. Thus, large molecules of RNA (single-stranded or double-stranded) consequently sliced into small molecules produce nascent small interfering RNA ranging from 21 to 27 nucleotides. This chapter revisits the biogenesis of these two types of RNAi, miRNA and siRNA, and notably their involvement in plant gene regulation. Following their sequential transcription and their specific involvement, we will consider the sources and roles of RNA interference in plants and we will look at their detection in fruit crops. We discuss their applications and the risk assessment studies in fruit crops.