Monday, December 17, 2018

Development in embryonic leaves of Setaria viridis

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Setaria viridis is being promoted as a model C4 photosynthetic plant because it has a small genome (~515Mb), a short life cycle (~60d) and it can be transformed. Unlike other C4 grasses such as maize, however, there is very little information about how C4 leaf anatomy (Kranz anatomy) develops in S. viridis. As a foundation for future developmental genetic studies, Junqueira and colleagues provide an anatomical and ultrastructural framework of early shoot development in S. viridis, focusing on the initiation of Kranz anatomy in seed leaves.

Scanning electron microscopy of <em>S. viridis</em> diaspore during germination from dry seed
Scanning electron microscopy of S. viridis diaspore during germination from dry seed to 36 h after imbibition (first embryonic leaf rupturing the coleoptile). (A) Stage S0 – dry seed – with bracts: first glume (*), second glume (**), sterile lemma (arrow) and fertile lemma (dashed arrow) enveloping the caryopsis (the palea remains covered by the sterile lemma). (B) Stage S1 – 12 h after imbibition, the coleorhiza rupturing the caryopsis (arrow). (C) Stage S2 – 15 h after imbibition, absorbent hairs of the coleorhiza (arrow) are visible. (D) Stage S3 – 24 h after imbibition, coleoptile breaking through the caryopsis (arrow); the radicle (*), the mesocotyl (dashed arrow) and coleorhiza (**) are visible. (E) Stage S4 – 36 h after imbibition, left: intact coleoptile; right: the first juvenile leaf has ruptured the coleoptile (arrow). (F) Ruptured coleoptile shown in detail. Scale bar = 500 μm (A, B, D), 1mm (C), 2 mm (E), 200 μm (F).

C4 plants of interest as they’re more efficient at photosynthesis than most plants, which are dubbed C3 as they first fix carbon into phosphoglyceric acid, a molecule with 3 carbon atoms. C4 plants have an extra step in photosynthesis, resulting in a reduced loss of water in photosynthesis. This ability to conserve water makes them of interest for crop development.

Reference List

Junqueira, N. E. G., Ortiz-Silva, B., Leal-Costa, M. V., Alves-Ferreira, M., Dickinson, H. G., Langdale, J. A., & Reinert, F. (2018). Anatomy and ultrastructure of embryonic leaves of the C4 species Setaria viridis. Annals of Botany, 121(6), 1163–1172. https://doi.org/10.1093/aob/mcx217

Snails use smell to select seedlings of favoured grassland species

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Although Darwin recognised long ago the destructive impact that snails and slugs have on seedlings, we understand remarkably little about why these herbivores select different plants at their most vulnerable stage. Hanley et al. examine the role of volatile compounds in the attractiveness of seedlings of 14 grassland species to snails (Cornu aspersum, Helicidae).

Cornu aspersum

Selection is closely associated with different volatile profiles; specifically snails used characteristic odour cues (smell) to select preferred seedlings. The study shows how seedling selection occurs before snail attack, and explains why some plants avoid herbivory and establish even when molluscs are active and abundant.

Reference List

Hanley, M. E., Shannon, R. W. R., Lemoine, D. G., Sandey, B., Newland, P. L., & Poppy, G. M. (2018). Riding on the wind: volatile compounds dictate selection of grassland seedlings by snails. Annals of Botany, 122(6), 1075–1083. https://doi.org/10.1093/aob/mcy190

Plants grow in winter on the eastern Qinghai-Tibetan Plateau

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Alpine plants growing on the Eastern Tibetan Plateau were thought to senesce or lie dormant during the winter, but after 4 years of field observations, Li et al. show how some species kept growing in this extremely cold and unpredictable environment.

Gentiana spathulifolia

One species, Gentiana spathulifolia (Gentianaceae) even flowers in winter and many others were conspicuous in terms of their allocation to above ground biomass, and contribution to establishment of the summer vegetation. The authors conclude that although often overlooked, these winter growth species are essential in our in understanding of Alpine ecosystem functions like carbon cycling and potentially community responses to climate change.

Reference List

Mo, L., Luo, P., Mou, C., Yang, H., Wang, J., Wang, Z., … Zuo, D. (2018). Winter plant phenology in the alpine meadow on the eastern Qinghai–Tibetan Plateau. Annals of Botany, 122(6), 1033–1045. https://doi.org/10.1093/aob/mcy112

Floral mimicry of Faboideae in an Australian orchid

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While there is increasing recognition of floral mimicry in plants, there are few cases where any explanatory mechanism is confirmed. Scaccabarozzi et al. test for pollination by mimicry in western Australian Diuris orchids, a genus hypothesized to attract pollinators by mimicking a range of sympatric Daviesia species Faboideae.

Diuris brumalis

The mimicry in this system was revealed by pollinator behaviour, examined using artificial clumps of orchids; like Daviesia, Diuris brumalis was pollinated by Trichocolletes spp. (Colletidae). Interestingly, D. brumalis belongs to a complex of species with similar floral traits, suggesting that this genus represents a useful system for investigating speciation in lineages that employ mimicry of food plants.

Reference List

Scaccabarozzi, D., Cozzolino, S., Guzzetti, L., Galimberti, A., Milne, L., Dixon, K. W., & Phillips, R. D. (2018). Masquerading as pea plants: behavioural and morphological evidence for mimicry of multiple models in an Australian orchid. Annals of Botany. https://doi.org/10.1093/aob/mcy166

Understanding glacial biogeographical patterns using environmental niche modelling and geostatistics

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Identifying Quaternary glacial refugia has been a major focus of biogeographical research efforts over the last century. The concept of refugia presumes a contraction in species range to a particular geographic area along with a reduction in its abundance due to unfavourable environmental conditions. The Balkan Peninsula represents one of the three southern European glacial refugia where biodiversity persisted throughout the climatically unstable Quaternary period.

The endemic species used in this study
The endemic plant Edraianthus tenuifolius. Image credit: Boštjan Surina.

In a recent study published in AoBP, Glasnović et al. combined species occurrence data with present and last glacial maximum environmental conditions. They coupled this with spatial analysis of phenotypic plasticity of floral characters to reveal the intricate biogeographic patterns of the endemic plant Edraianthus tenuifolius within the Balkan Peninsula. The species showed patterns of geographical variation that strongly support the ‘refugia within refugia’ concept, which assumes environmental heterogeneity over time and space within larger refugia. Both environmental niche modelling and the geographical variability of morphological characters suggested spatial partitioning, indicating the potential presence of two separate refugia during the LGM. The results from this work support the findings of previous studies that recognised refugial areas for thermophytic plant taxa during the glacial events of the Pleistocene. However, detecting areas that represent potential ice age refugia is just the beginning of understanding biodiversity processes on a geographical level. Further efforts are now needed to address the mechanisms that have led to present day-diversity in terms of environmental changes and ecological processes through recent Earth history.

Researcher highlight

Peter Glasnović

Peter Glasnović is a botany enthusiast, who obtained a BSc in Biology and Chemistry from the University of Ljubljana, Slovenia in 2006. In 2017 he completed a PhD in biogeography at the University of Primorska, Slovenia under the supervision of Professor Boštjan Surina and Professor Valentina Brečko Grubar.

Peter currently works as an assistant at the Faculty of Mathematics, Natural Sciences and Information Technologies of the University of Primorska, Slovenia. He is involved in courses of Systematic Botany, Biogeography and GIS. His scientific interests are plant biology and geographical patterns of plant diversity in the Mediterranean and in the Balkan Peninsula.

Reference List

Glasnović, P., Temunović, M., Lakušić, D., Rakić, T., Grubar, V. B., & Surina, B. (2018). Understanding biogeographical patterns in the western Balkan Peninsula using environmental niche modelling and geostatistics in polymorphic Edraianthus tenuifolius. AoB PLANTS. https://doi.org/10.1093/aobpla/ply064

Male reproductive success and floral trait evolution in animal-pollinated plants

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More than 85% of flowering plant species require the services of foraging animal pollinators to transfer male gametes (pollen) to stigmas of potential mates. The vast majority (95-99%) of pollen grains produced by a plant never successfully fertilize ovules, and are instead lost during the complex and chaotic process of pollen transport. For example, some pollen grains fall to the ground as the pollinator picks up pollen or following intense gusts of wind. Other grains are deposited onto the pollinator, but then groomed to pollen carrying baskets or other locations where the grains will no longer contact stigmas of potential mates. Still other pollen grains are buried by pollen from rival males visited subsequently by the pollinator. Recent research suggests that flowering plants have evolved numerous mechanisms to increase the efficiency of the pollen transport process.

Dimorphotheca pollen is deposited onto a fly Corsomyza as it probes a flower for nectar.
Dimorphotheca pollen is deposited onto a fly Corsomyza as it probes a flower for nectar. Photo by Bruce Anderson.

A new Review by Minnaar et al. in Annals of Botany explores the intricate “pathway to paternity” in flowering plants, and highlights the evolution of pollination strategies that favor male reproductive success. In particular, they describe bodies of pollinators as arenas for pollen competition where rival males constantly cover or displace competitor pollen. This work provides important new insights about how sexual selection operates in flowering plant populations. The paper is beautifully illustrated with many stunning photos of the pollination process.

Reference List

Minnaar, C., Anderson, B., de Jager, M. L., & Karron, J. D. (2018). Plant–pollinator interactions along the pathway to paternity. Annals of Botany. https://doi.org/10.1093/aob/mcy167

Multiple parallel dispersal events and mosaic genetic structure in Dactylorhiza

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Orchids have minute seeds and can disperse over long distances. Hedrén et al. use genetic markers to track how the marsh orchid Dactylorhiza majalis ssp. lapponica (Orchidaceae) colonised the Baltic Sea island of Gotland repeatedly (and mostly from the east) after the last ice age.

Dactylorhiza majalis ssp. lapponica

These multiple colonization events have resulted in a mosaic pattern of genetic variation, such that adjacent populations are not necessarily closely related. Hedrénet al. also find that the genetically most diverse populations are located at older sites, suggesting that genetic diversity builds up over time.

Reference List

Hedrén, M., Olofsson, S. N., & Paun, O. (2018). Orchid colonization: multiple parallel dispersal events and mosaic genetic structure in Dactylorhiza majalis ssp. lapponica on the Baltic island of Gotland. Annals of Botany. https://doi.org/10.1093/aob/mcy111

Unmasking cryptic biodiversity in polyploids

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Up to one-quarter of flowering plant species may have escaped recognition due to processes such as autopolyploidy-whole genome duplication events where polyploids may be morphologically identical to their diploid progenitors. Mairal et al. combine macroevolutionary, microevolutionary and niche modelling tools to disentangle the origin and demographic history of the polyploid complex of Aster amellus (Asteraceae).

Aster amellus
Aster amellus distribution.

They demonstrate that diploid and hexaploid A. amellus may be considered as two independent lineages at the onset of their diversification, with separate niches and different evolutionary histories. The considerable cryptic diversity of polyploid taxa should be thus further evaluated in order to obtain a full picture of global angiosperm biodiversity.

Reference List

Mairal, M., Šurinová, M., Castro, S., & Münzbergová, Z. (2018). Unmasking cryptic biodiversity in polyploids: origin and diversification of Aster amellus aggregate. Annals of Botany. https://doi.org/10.1093/aob/mcy149

The loss of genetic diversity threatens the last Afro-Macaronesian subtropical forests

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Subtropical African forests are on the verge of extinction due to a long history of exploitation. Considered sanctuaries of exceptional biodiversity, they shelter many endemic and irreplaceable species. Some component plant species remain widely distributed however, and by studying their demographic history, we might understand better the fate of these threatened ecosystems.

A drawing of a loss of diversity

Mairal et al. use molecular and ecological niche modelling approaches to assess the demographic evolution of Canarina (Campanulaceae) a rare and relict plant species, but one widely distributed in Afro-Macaronesian subtropical forests. The authors report an alarming recent demographic decline in the species, highlighting how locally widespread endemics may be threatened by habitat loss. The extinction debt, and extinction spiral to which these populations are subject, demands urgent conservation measures for the last world remnants of these important forests.

Reference List

Mairal, M., Caujapé-Castells, J., Pellissier, L., Jaén-Molina, R., Álvarez, N., Heuertz, M., & Sanmartín, I. (2018). A tale of two forests: ongoing aridification drives population decline and genetic diversity loss at continental scale in Afro-Macaronesian evergreen-forest archipelago endemics. Annals of Botany, 122(6), 1005–1017. https://doi.org/10.1093/aob/mcy107

Genome-wide identification of long non-coding RNA targets of the tomato MADS box transcription factor RIN and function analysis

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In recent years, increasing numbers of long non-coding RNAs (lncRNAs) have been identified in humans, animals and plants, and several of them have been shown to play important roles in diverse biological processes. However, little work has been performed on the regulation mechanism of lncRNA biogenesis and expression, especially in plants. Compared with studies of tomato MADS-box transcription factor RIPENING INHIBITOR (RIN) target coding genes, there are few reports on its relationship to non-coding RNAs. The aim of the present study was to identify and explore the specific role of RIN target lncRNAs in tomato fruit development and ripening.

Schematic representation of the proposed model for a regulatory mechanism of tomato fruit ripenin
Schematic representation of the proposed model for a regulatory mechanism of tomato fruit ripening. Full-line arrows indicate RIN regulates fruit ripening by ethylene via ACS4 and ripening-related target genes. Dotted-line arrow indicates that the regulatory mechanism of lncRNAs during fruit ripening is unclear.

lncRNA targets of RIN were identified by chromatin immunoprecipitation sequencing (ChIP-seq) combined with RNA deep sequencing analysis. Yu et al. identified 187 lncRNAs as direct RIN targets, which exhibited RIN binding sites in their promoters and showed different expression between the wild-type and rin mutant. Six target lncRNAs were shown to bind with RIN directly in their promoters in vivo and in vitro. Moreover, using CRISPR/Cas9 technology to knock out the locus of the target lncRNA2155 indicated that it delayed fruit ripening in tomato.

Collectively, these findings provide new insight into RIN in the transcriptional regulation of lncRNAs and suggest that lncRNAs will contribute to a better understanding of the RIN regulatory network that controls fruit ripening.

Reference List

Yu, T., Tzeng, D. T. W., Li, R., Chen, J., Zhong, S., Fu, D., … Zhu, H. (2018). Genome-wide identification of long non-coding RNA targets of the tomato MADS box transcription factor RIN and function analysis. Annals of Botany. https://doi.org/10.1093/aob/mcy178

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