In-depth investigation of any developmental process in plants requires knowledge of both the underpinning molecular networks and how they directly determine patterns of cell division and expansion ...over time. Floral meristems (FMs) produce floral organs, after which they undergo floral meristem termination (FMT); precise control of organ initiation and FMT is crucial to the reproductive success of any flowering plant. Using live confocal imaging, we characterized developmental dynamics during floral organ primordia initiation and FMT in Aquilegia coerulea (Ranunculaceae). Our results uncover distinct patterns of primordium initiation between stamens and staminodes compared with carpels, and provide insight into the process of FMT, which is discernable based on cell division dynamics that precede carpel initiation. To our knowledge, this is the first quantitative live imaging of meristem development in a system with numerous whorls of floral organs, as well as an apocarpous gynoecium. This study provides crucial information for our understanding of how the spatial-temporal regulation of floral meristem behavior is achieved in both evolutionary and developmental contexts. This article has an associated 'The people behind the papers' interview.
As the sister group to seed plants, ferns are a phylogenetically informative lineage. Functional studies in representatives of the fern lineage are helping bridge the knowledge gap in developmental ...mechanisms between angiosperms and non-vascular plants. The fern life cycle has the advantage of combining a sizable free-living haploid gametophyte, more amenable for developmental studies than the reduced seed plant gametophyte, with an indeterminate and complex diploid sporophyte. Ceratopteris richardii has long been proposed as a model fern and has recently become tractable due to stable transgenesis and increasing genomic resources, allowing researchers to test explicit questions about gene function in a fern for the first time. As with any model system, a detailed understanding of wild-type morphology and a staged ontogeny are indispensable for the characterization of mutant phenotypes resulting from genetic manipulations. Therefore, the goal of this study is to provide a unified reference ontogeny for this emerging model fern as a tool for comparative evolutionary and developmental studies. It complements earlier research by filling gaps in major stages of development of the haploid gametophyte and diploid sporophyte generations, and provides additional descriptions of the shoot apical meristem and early leaf development. This resource is meant to facilitate not only studies of candidate genes within C. richardii, but also broader ontogenetic comparisons to other model plants.
•Ceratopteris richardii is becoming a tractable model fern, with stable transgenesis and genetic resources.•Morphological landmarks deliver a unified developmental staging system across the Ceratopteris life cycle.•This reference ontogeny provides a framework for phenotypic characterizations of gametophyte and sporophyte generations.
Abstract
Background and Aims
Aquilegia produce elongated, three-dimensional petal spurs that fill with nectar to attract pollinators. Previous studies have shown that the diversity of spur length ...across the Aquilegia genus is a key innovation that is tightly linked with its recent and rapid diversification into new ranges, and that evolution of increased spur lengths is achieved via anisotropic cell elongation. Previous work identified a brassinosteroid response transcription factor as being enriched in the early developing spur cup. Brassinosteroids are known to be important for cell elongation, suggesting that brassinosteroid-mediated response may be an important regulator of spur elongation and potentially a driver of spur length diversity in Aquilegia. In this study, we investigated the role of brassinosteroids in the development of the Aquilegia coerulea petal spur.
Methods
We exogenously applied the biologically active brassinosteroid brassinolide to developing petal spurs to investigate spur growth under high hormone conditions. We used virus-induced gene silencing and gene expression experiments to understand the function of brassinosteroid-related transcription factors in A. coerulea petal spurs.
Key Results
We identified a total of three Aquilegia homologues of the BES1/BZR1 protein family and found that these genes are ubiquitously expressed in all floral tissues during development, yet, consistent with the previous RNAseq study, we found that two of these paralogues are enriched in early developing petals. Exogenously applied brassinosteroid increased petal spur length due to increased anisotropic cell elongation as well as cell division. We found that targeting of the AqBEH genes with virus-induced gene silencing resulted in shortened petals, a phenotype caused in part by a loss of cell anisotropy.
Conclusions
Collectively, our results support a role for brassinosteroids in anisotropic cell expansion in Aquilegia petal spurs and highlight the brassinosteroid pathway as a potential player in the diversification of petal spur length in Aquilegia.
In this study, we present a detailed protocol for live imaging and quantitative analysis of floral meristem development in
, a member of the buttercup family (Ranunculaceae). Using confocal ...microscopy and the image analysis software MorphoGraphX, we were able to examine the cellular growth dynamics during floral organ primordia initiation, and the transition from floral meristem proliferation to termination. This protocol provides a powerful tool to study the development of the meristem and floral organ primordia, and should be easily adaptable to many plant lineages, including other emerging model systems. It will allow researchers to explore questions outside the scope of common model systems.
SUMMARY
Members of the YABBY gene family of transcription factors in angiosperms have been shown to be involved in the initiation of outgrowth of the lamina, the maintenance of polarity, and ...establishment of the leaf margin. Although most of the dorsal‐ventral polarity genes in seed plants have homologs in non‐spermatophyte lineages, the presence of YABBY genes is restricted to seed plants. To gain insight into the origin and diversification of this gene family, we reconstructed the evolutionary history of YABBY gene lineages in seed plants. Our findings suggest that either one or two YABBY genes were present in the last common ancestor of extant seed plants. We also examined the expression of YABBY genes in the gymnosperms Ephedra distachya (Gnetales), Ginkgo biloba (Ginkgoales), and Pseudotsuga menziesii (Coniferales). Our data indicate that some YABBY genes are expressed in a polar (abaxial) manner in leaves and female cones in gymnosperms. We propose that YABBY genes already acted as polarity genes in the last common ancestor of extant seed plants.
During land plant evolution, determinate spore-bearing axes (retained in extant bryophytes such as mosses) were progressively transformed into indeterminate branching shoots with specialized ...reproductive axes that form flowers. The LEAFY transcription factor, which is required for the first zygotic cell division in mosses and primarily for floral meristem identity in flowering plants, may have facilitated developmental innovations during these transitions. Mapping the LEAFY evolutionary trajectory has been challenging, however, because there is no functional overlap between mosses and flowering plants, and no functional data from intervening lineages. Here, we report a transgenic analysis in the fern
that reveals a role for LEAFY in maintaining cell divisions in the apical stem cells of both haploid and diploid phases of the lifecycle. These results support an evolutionary trajectory in which an ancestral LEAFY module that promotes cell proliferation was progressively co-opted, adapted and specialized as novel shoot developmental contexts emerged.
We present a multiyear time series of column abundances of carbon monoxide (CO), hydrogen cyanide (HCN), and ethane (C2H6) measured using Fourier-transform infrared (FTIR) spectrometers at 10 sites ...affiliated with the Network for the Detection of Atmospheric Composition Change (NDACC). Six are high-latitude sites: Eureka, Ny-Ålesund, Thule, Kiruna, Poker Flat, and St. Petersburg, and four are midlatitude sites: Zugspitze, Jungfraujoch, Toronto, and Rikubetsu. For each site, the interannual trends and seasonal variabilities of the CO time series are accounted for, allowing background column amounts to be determined. Enhancements above the seasonal background were used to identify possible wildfire pollution events. Since the abundance of each trace gas emitted in a wildfire event is specific to the type of vegetation burned and the burning phase, correlations of CO to the long-lived wildfire tracers HCN and C2H6 allow for further confirmation of the detection of wildfire pollution. A GEOS-Chem tagged CO simulation with Global Fire Assimilation System (GFASv1.2) biomass burning emissions was used to determine the source attribution of CO concentrations at each site from 2003 to 2018. For each detected wildfire pollution event, FLEXPART back-trajectory simulations were performed to determine the transport times of the smoke plume. Accounting for the loss of each species during transport, the enhancement ratios of HCN and C2H6 with respect to CO were converted to emission ratios. We report mean emission ratios with respect to CO for HCN and C2H6 of 0.0047 and 0.0092, respectively, with a standard deviation of 0.0014 and 0.0046, respectively, determined from 23 boreal North American wildfire events. Similarly, we report mean emission ratios for HCN and C2H6 of 0.0049 and 0.0100, respectively, with a standard deviation of 0.0025 and 0.0042, respectively, determined from 39 boreal Asian wildfire events. The agreement of our emission ratios with literature values illustrates the capability of ground-based FTIR measurements to quantify biomass burning emissions. We provide a comprehensive dataset that quantifies HCN and C2H6 emission ratios from 62 wildfire pollution events. Our dataset provides novel emission ratio estimates, which are sparsely available in the published literature, particularly for boreal Asian sources.
Premise of research. The structure and organization of the conifer shoot apical meristem was investigated using confocal microscopy of whole-mount shoot apical meristems. This article presents ...detailed surface and internal patterns that provide an informative and comparative model of meristem growth that is able to account for the diversity and variation of conifer meristem form.
Methodology. Confocal microscopy; light microscopy.
Pivotal results. On the surface of the meristem, two zones with distinct cell division patterns were recognized. The first is the summit zone that covers the apex of the meristem dome, and the second is the peripheral zone that covers the flanks of the meristem. In the summit zone, successive anticlinal cell divisions are perpendicular to each other and produce isotropic growth. In the peripheral zone, surface cells divide with repetitive transverse divisions to form long axial chains that create packets with anisotropic growth. Only cells in the summit zone divide periclinally to contribute daughter cells to the underlying tissue. Those meristems with a small number of cells in the summit zone have a correspondingly small number of periclinal divisions of apical initial cells. Those meristems with larger summit zones and many wedge-shaped packets have a larger number of apical initials dividing periclinally.
Conclusions. Conifer meristems have consistent cell division patterns that define the summit and peripheral zones. Apical initials are transient, and their number varies between meristems, depending on the size of the summit zone.
In this study, we present a detailed protocol for live imaging and quantitative analysis of floral meristem development in
Aquilegia coerulea
, a member of the buttercup family (Ranunculaceae). Using ...confocal microscopy and the image analysis software MorphoGraphX, we were able to examine the cellular growth dynamics during floral organ primordia initiation, and the transition from floral meristem proliferation to termination. This protocol provides a powerful tool to study the development of the meristem and floral organ primordia, and should be easily adaptable to many plant lineages, including other emerging model systems. It will allow researchers to explore questions outside the scope of common model systems.
Changes of atmospheric methane total columns (CH4) since 2005 have been evaluated using Fourier transform infrared (FTIR) solar observations carried out at 10 ground-based sites, affiliated to the ...Network for Detection of Atmospheric Composition Change (NDACC). From this, we find an increase of atmospheric methane total columns of 0.31 ± 0.03 % year−1 (2σ level of uncertainty) for the 2005–2014 period. Comparisons with in situ methane measurements at both local and global scales show good agreement. We used the GEOS-Chem chemical transport model tagged simulation, which accounts for the contribution of each emission source and one sink in the total methane, simulated over 2005–2012. After regridding according to NDACC vertical layering using a conservative regridding scheme and smoothing by convolving with respective FTIR seasonal averaging kernels, the GEOS-Chem simulation shows an increase of atmospheric methane total columns of 0.35 ± 0.03 % year−1 between 2005 and 2012, which is in agreement with NDACC measurements over the same time period (0.30 ± 0.04 % year−1, averaged over 10 stations). Analysis of the GEOS-Chem-tagged simulation allows us to quantify the contribution of each tracer to the global methane change since 2005. We find that natural sources such as wetlands and biomass burning contribute to the interannual variability of methane. However, anthropogenic emissions, such as coal mining, and gas and oil transport and exploration, which are mainly emitted in the Northern Hemisphere and act as secondary contributors to the global budget of methane, have played a major role in the increase of atmospheric methane observed since 2005. Based on the GEOS-Chem-tagged simulation, we discuss possible cause(s) for the increase of methane since 2005, which is still unexplained.
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