skip to main content


The NSF Public Access Repository (NSF-PAR) system and access will be unavailable from 11:00 PM ET on Thursday, May 23 until 2:00 AM ET on Friday, May 24 due to maintenance. We apologize for the inconvenience.

Title: The YABBY gene SHATTERING1 controls activation rather than patterning of the abscission zone in Setaria viridis

Abscission is predetermined in specialized cell layers called the abscission zone (AZ) and activated by developmental or environmental signals. In the grass family, most identified AZ genes regulate AZ anatomy, which differs among lineages. A YABBY transcription factor,SHATTERING1(SH1), is a domestication gene regulating abscission in multiple cereals, including rice andSetaria. In rice,SH1inhibits lignification specifically in the AZ. However, the AZ ofSetariais nonlignified throughout, raising the question of howSH1functions in species without lignification.

Crispr‐Cas9 knockout mutants ofSH1were generated inSetaria viridisand characterized with histology, cell wall and auxin immunofluorescence, transmission electron microscopy, hormonal treatment and RNA‐Seq analysis.

Thesh1mutant lacks shattering, as expected. No differences in cell anatomy or cell wall components including lignin were observed betweensh1and the wild‐type (WT) until abscission occurs. Chloroplasts degenerated in the AZ of WT before abscission, but degeneration was suppressed by auxin treatment. Auxin distribution and expression of auxin‐related genes differed between WT andsh1, with the signal of an antibody to auxin detected in thesh1chloroplast.

SH1inSetariais required for activation of abscission through auxin signaling, which is not reported in other grass species.

more » « less
Award ID(s):
Author(s) / Creator(s):
 ;  ;  ;  ;  
Publisher / Repository:
Date Published:
Journal Name:
New Phytologist
Medium: X Size: p. 846-862
["p. 846-862"]
Sponsoring Org:
National Science Foundation
More Like this
  1. Summary

    Abscission is a process in which plants shed their parts, and is mediated by a particular set of cells, the abscission zone (AZ). In grasses (Poaceae), the position of the AZ differs among species, raising the question of whether its anatomical structure and genetic control are conserved.

    The ancestral position of the AZ was reconstructed. A combination of light microscopy, transmission electron microscopy, RNA‐Seq analyses and RNAin situhybridisation were used to compare three species, two (weedy rice andBrachypodium distachyon) with the AZ in the ancestral position and one (Setaria viridis) with the AZ in a derived position below a cluster of flowers (spikelet).

    Rice andBrachypodiumare more similar anatomically thanSetaria. However, the cell wall properties and the transcriptome of rice andBrachypodiumare no more similar to each other than either is toSetaria. The set of genes expressed in the studied tissues is generally conserved across species, but the precise developmental and positional patterns of expression and gene networks are almost entirely different.

    Transcriptional regulation of AZ development appears to be extensively rewired among the three species, leading to distinct anatomical and morphological outcomes.

    more » « less
  2. Abstract Abscission, known as shattering in crop species, is a highly regulated process by which plants shed parts. Although shattering has been studied extensively in cereals and a number of regulatory genes have been identified, much diversity in the process remains to be discovered. Teff (Eragrostis tef) is a crop native to Ethiopia that is potentially highly valuable worldwide for its nutritious grain and drought tolerance. Previous work has suggested that grain shattering in Eragrostis might have little in common with other cereals. In this study, we characterize the anatomy, cellular structure, and gene regulatory control of the abscission zone (AZ) in E. tef. We show that the AZ of E. tef is a narrow stalk below the caryopsis, which is common in Eragrostis species. X-ray microscopy, scanning electron microscopy, transmission electron microscopy, and immunolocalization of cell wall components showed that the AZ cells are thin walled and break open along with programmed cell death (PCD) at seed maturity, rather than separating between cells as in other studied species. Knockout of YABBY2/SHATTERING1, documented to control abscission in several cereals, had no effect on abscission or AZ structure in E. tef. RNA sequencing analysis showed that genes related to PCD and cell wall modification are enriched in the AZ at the early seed maturity stage. These data show that E. tef drops its seeds using a unique mechanism. Our results provide the groundwork for understanding grain shattering in Eragrostis and further improvement of shattering in E. tef. 
    more » « less
  3. Premise

    Abscission zones (AZ) are specialized cell layers that separate plant parts at the organ junction upon developmental or environmental signals. Fruit or seed abscission has been well studied in model species because of its crucial role for seed dispersal. Previous work showed thatAZlocalization differs among species of Poaceae and thatAZformation is histologically and genetically distinct in three distantly related grass species, refuting the idea of a broadly conserved module. However, whetherAZstructure is consistent within subfamilies is unknown.


    Eleven species were selected from six subfamilies of Poaceae, and theirAZwas investigated using paraffin‐embedded, stained material. Observations were added from the literature for an additional six species. Data were recorded onAZlocation and whether cells in theAZwere distinguishable by size or lignification. Characteristics of theAZwere mapped on the phylogeny using maximum likelihood.


    Abscission zone anatomy and histology vary among species, and characteristics of theAZdo not correlate with phylogeny. Twelve of the seventeen studied species have anAZin which the cells are significantly smaller than surrounding cells. Of these, eight have differential lignification. Differential lignification is often associated with differential cell size, but not vice versa.


    Neither smaller cells in theAZnor differential lignification between the AZand surrounding cells is required for abscission, although differential cell size and lignification are often correlated. Abscission zone anatomy does not correlate with phylogeny, suggesting its rapid change over evolutionary time.

    more » « less
  4. Summary

    Style length is a major determinant of breeding strategies in flowering plants and can vary dramatically between and within species. However, little is known about the genetic and developmental control of style elongation.

    We characterized the role of two classes of leaf adaxial–abaxial polarity factors, SUPPRESSOR OF GENE SILENCING3 (SGS3) and the YABBY family transcription factors, in the regulation of style elongation inMimulus lewisii. We also examined the spatiotemporal patterns of auxin response during style development.

    Loss ofSGS3function led to reduced style length via limiting cell division, and downregulation ofYABBYgenes by RNA interference resulted in shorter styles by decreasing both cell division and cell elongation. We discovered an auxin response minimum between the stigma and ovary during the early stages of pistil development that marks style differentiation. Subsequent redistribution of auxin response to this region was correlated with style elongation. Auxin response was substantially altered when bothSGS3andYABBYfunctions were disrupted.

    We suggest that auxin signaling plays a central role in style elongation and that the way in which auxin signaling controls the different cell division and elongation patterns underpinning natural style length variation is a major question for future research.

    more » « less
  5. Summary

    Plant embryogenesis results from the fusion of male and female gametes but can also be induced in somatic cells. The molecular pathways for embryo initiation are poorly understood, especially in monocots. In rice, the male gamete expressed BABY BOOM1 (OsBBM1) transcription factor functions as an embryogenic trigger in the zygote and can also promote somatic embryogenesis when ectopically expressed in somatic tissues.

    We used gene editing, transcriptome profiling, and chromatin immunoprecipitation to determine the molecular players involved in embryo initiation downstream ofOsBBM1.

    We identifyOsYUCCA(OsYUC) auxin biosynthesis genes as direct targets ofOsBBM1. Unexpectedly, theseOsYUCtargets in zygotes are expressed only from the maternal genome, whereas the paternal genome exclusively provides functionalOsBBM1to initiate embryogenesis. Induction of somatic embryogenesis by exogenous auxin requiresOsBBMgenes and downstreamOsYUCtargets. EctopicOsBBM1initiates somatic embryogenesis without exogenous auxins but requires functionalOsYUCgenes.

    Thus, anOsBBM‐OsYUCmodule is a key player for both somatic and zygotic embryogenesis in rice. Zygotic embryo initiation involves a partnership of male and female genomes, through which paternalOsBBM1activates maternalOsYUCgenes. In somatic embryogenesis, exogenous auxin triggersOsBBM1expression, which then activates endogenous auxin biosynthesisOsYUCgenes.

    more » « less