Boundary Formation through a Direct Threshold-Based Readout of Mobile Small RNA Gradients.

Small RNAs have emerged as a new class of mobile signals. Here, we investigate their mechanism of action and show that mobile small RNAs generate sharply defined domains of target gene expression through an intrinsic and direct threshold-based readout of their mobility gradients. This readout is highly sensitive to small RNA levels at the source, allowing plasticity in the positioning of a target gene expression boundary.

The ASYMMETRIC LEAVES Complex Employs Multiple Modes of Regulation to Affect Adaxial-Abaxial Patterning and Leaf Complexity.

Flattened leaf architecture is not a default state but depends on positional information to precisely coordinate patterns of cell division in the growing primordium. This information is provided, in part, by the boundary between the adaxial (top) and abaxial (bottom) domains of the leaf, which are specified via an intricate gene regulatory network whose precise circuitry remains poorly defined. Here, we examined the contribution of the ASYMMETRIC LEAVES (AS) pathway to adaxial-abaxial patterning in Arabidopsis thaliana and demonstrate that AS1-AS2 affects this process via multiple, distinct regulatory mechanisms.

Developmental patterning by gradients of mobile small RNAs.

Development of multicellular organisms depends on intercellular communication via mobile signals that provide positional information to coordinate cell fate decisions. In addition to peptide ligands, transcription factors, and hormones, plants use small RNAs as positional instructive signals. The unique patterning properties of small RNA gradients resulting from regulated mobility suggest conceptual similarities to the function of animal morphogens, and provide robustness and precision to the formation of cell fate boundaries.

Plant nonsense-mediated mRNA decay is controlled by different autoregulatory circuits and can be induced by an EJC-like complex.

Nonsense-mediated mRNA decay (NMD) is a eukaryotic quality control system that recognizes and degrades transcripts containing NMD cis elements in their 3'untranslated region (UTR). In yeasts, unusually long 3'UTRs act as NMD cis elements, whereas in vertebrates, NMD is induced by introns located >50 nt downstream from the stop codon. In vertebrates, splicing leads to deposition of exon junction complex (EJC) onto the mRNA, and then 3'UTR-bound EJCs trigger NMD.

The late steps of plant nonsense-mediated mRNA decay.

Nonsense-mediated mRNA decay (NMD) is a eukaryotic quality control system that identifies and degrades mRNAs containing premature termination codons (PTCs). If translation terminates at a PTC, the UPF1 NMD factor binds the terminating ribosome and recruits UPF2 and UPF3 to form a functional NMD complex, which triggers the rapid decay of the PTC-containing transcript. Although NMD deficiency is seedling lethal in plants, the mechanism of plant NMD remains poorly understood.

Functional analysis of the grapevine paralogs of the SMG7 NMD factor using a heterolog VIGS-based gene depletion-complementation system.

Nonsense-mediated mRNA decay (NMD) is a eukaryotic quality control system that identifies and eliminates transcripts having a premature translation termination codon (PTC). NMD is also involved in the control of several wild-type mRNAs. The NMD core machinery consists of three highly conserved NMD factors (UPF1, UPF2 and UPF3) and at least one less conserved 14-3-3-like domain containing protein (SMG7).

Plant upstream ORFs can trigger nonsense-mediated mRNA decay in a size-dependent manner.

Nonsense-mediated decay (NMD) is a quality control mechanism that identifies and degrades aberrant mRNAs containing premature termination codons (PTC). NMD also regulates the expression of many wild-type genes. In plants, NMD identifies a stop codon as a PTC and initiates the rapid degradation of the transcript if the 3'untranslated region (UTR) is unusually long or if it harbors an intron.