Orchid pollen, clover and salinity and Arabidopsis REM – This Week in Annals of Botany

Dactylorhiza maculata Desiccation tolerance, longevity and seed-siring ability of entomophilous pollen from UK native orchid species
Pollinator-limited seed-set in some terrestrial orchids is compensated for by the presence of long-lived flowers. This study tests the hypothesis that pollen from these insect-pollinated orchids should be desiccation tolerant and relatively long lived using four closely related UK terrestrial species; Anacamptis morio, Dactylorhiza fuchsii, D. maculata and Orchis mascula.

 

Heritability and quantitative genetic divergence of serotiny, a fire-persistence plant trait
Although it is well known that fire acts as a selective pressure shaping plant phenotypes, there are no quantitative estimates of the heritability of any trait related to plant persistence under recurrent fires, such as serotiny. In this study, the heritability of serotiny in Pinus halepensis is calculated, and an evaluation is made as to whether fire has left a selection signature on the level of serotiny among populations by comparing the genetic divergence of serotiny with the expected divergence of neutral molecular markers.

 

Leaf hydraulic vulnerability to drought is linked to site water availability across a broad range of species and climates
Vulnerability of the leaf hydraulic pathway to water-stress-induced dysfunction is a key component of drought tolerance in plants and may be important in defining species’ climatic range. However, the generality of the association between leaf hydraulic vulnerability and climate across species and sites remains to be tested.

 

Salinity-mediated cyanogenesis in white clover (Trifolium repens) affects trophic interactions
Increasing soil salinity poses a major plant stress in agro-ecosystems worldwide. Surprisingly little is known about the quantitative effect of elevated salinity on secondary metabolism in many agricultural crops. Such salt-mediated changes in defence-associated compounds may significantly alter the quality of food and forage plants as well as their resistance against pests. In this study, the effects of soil salinity on cyanogenesis in white clover (Trifolium repens), a forage crop of international importance, are analysed.

 

Analysis of the arabidopsis REM gene family predicts functions during flower development
The REM (Reproductive Meristem) gene family of Arabidopsis thaliana is part of the B3 DNA-binding domain superfamily. Despite the fact that several groups have worked on the REM genes for many years, little is known about the function of this transcription factor family. This study aims to identify a set of REM genes involved in flower development and to characterize their function.

 

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Prosopis: A global assessment of the biogeography, benefits, impacts and management of one of the world’s worst woody invasive plant taxa

14023S1R1Invasive species cause ecological, economic and social impacts and are key drivers of global change. This is the case for the genus Prosopis (mesquite; Fabaceae) where several taxa are among the world’s most damaging invasive species. Prosopis taxa are currently naturalised or invasive in 103 countries and are bioclimatically suitable for many more. There are numerous management practices available to control Prosopis invasions, each with their benefits and costs, however, in most areas management has had only limited success. In a new article published in AoB PLANTS, Shackleton et al. present a global review of Prosopis, focusing on its distribution, impacts, benefits and approaches to management. Key gaps in knowledge and promising options for management are highlighted.

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Variation of genes responsible for maturity loci in soybean

Variation of genes responsible for maturity loci in soybean

Variation of genes responsible for maturity loci in soybean

Soybean (Glycine max) is a typical short-day plant and several loci controlling flowering have been characterized. Whilst genes have been identified for loci E1 to E4, their degree of natural variation is unknown. Tsubokura et al. determine the sequences of these genes and their flanking regions for 39 accessions by primer walking, and perform systematic discrimination among alleles using DNA markers. Allelic combinations at the E1 to E4 loci are found to be associated with ecological types and about 62–66 % of variation of flowering time can be attributed to the loci. The results therefore suggest the existence of unidentified genes for flowering in soybean.

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One of a kind…

Image: Scott Zona/Wikimedia Commons.

Image: Scott Zona/Wikimedia Commons.

These articles have been going long enough(!) to be able now to report a successful outcome to a research project whose initiation was announced in a former news item entitled ‘Old meets new’. The project is the elucidation of the genome of Amborella trichopoda. “Amborella is a monotypic genus of rare understory [sic! What ever happened to understorEy??? - Ed.] shrubs or small trees endemic to… New Caledonia”.

Not only is this plant rare and monotypic – truly ‘one of a kind’! – but it is also probably the living – extant – flowering plant [angiosperm] that is closest evolutionarily to the earliest true first member of the angiosperm plant group, and may therefore be “the last survivor of a lineage that branched off during the dynasty’s earliest days, before the rest of the 350,000 or so angiosperm species diversified”. Given Amborella’s exalted status (which “represents the equivalent of the duck-billed platypus in mammals”), it is hoped that understanding its genetics will shed light on the evolution of the angiosperms as a whole. Indeed, the University of Bonn’s Dietmar Quandt is reported as describing Amborella as a more worthy model organism than Arabidopsis(!!!).

Since the angiosperms are probably the most ‘successful’ of all the groups in the Plant Kingdom (‘the land plants’, the Plantae), hopes are understandably high that unravelling the genome of Amborella – reported by the aptly named Amborella Genome Project – will lead to the identification of “the molecular basis of biological innovations that contributed to their geologically near-instantaneous rise to ecological dominance”. And accompanying the main nuclear genome article, Danny Rice et al. report on Amborella’s mitochondrial genome (mitochondria have some of their own DNA additional to that located in the nucleus) and find that numerous genes were acquired by horizontal gene transfer from other plants, including almost four entire mitochondrial genomes from mosses and algae. So, as ancient as it is, Amborella was still prepared to ‘learn’ from the experiences of even older land plants – mosses – and plant-like algae (which are in a different kingdom entirely to the land plants, the Protista). Adopt and adapt: a life lesson for all living things, I suggest.

[For more on this fascinating story, visit the home of the Amborella genome database. And if you still need some ‘proper’ botany (after all this genomery), you need look no further than Paula Rudall and Emma Knowles’ paper examining ultrastructure of stomatal development in early-divergent angiosperms (including Amborella…).  Notwithstanding all of this understandable present-day excitement, I can’t help but think that the importance of Amborella was foretold many decades ago, as "popular-in-the-mid-1970s" British-based pop band Fox seemingly declared: "things can get much better, under your Amborella…". Indeed! So, arabidopsis had better watch out! – Ed.]

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Reproduction and invasiveness in St. John’s wort

Reproduction and invasiveness in St. John’s wort

Reproduction and invasiveness in St. John’s wort

The relative ability of different plant taxa to invade new biogeographic regions successfully is dependent upon a number of biological and physical factors, one of which is the reproductive system, which directly influences population structure, gene flow and evolutionary potential. Considering seed formation, plants can reproduce through sex (selfing and outcrossing) or apomixis (asexual reproduction through seed.

St. John’s wort (Hypericum perforatum) is such an invasive species which is indigenous to central and eastern Europe; it is self-compatible and can reproduce through sex or apomixis. H. perforatum has successfully invaded North America since the first record of introduction in Lancaster, Pennsylvania in 1793. Its high genotypic plasticity in conjunction with variable levels of facultative apomixis are hypothesized to have contributed to its rapid spread throughout the continent. For example, in an analysis of multiple phenotypic traits, Maron et al. (2004) demonstrated that the introduction of H. perforatum into North America was accompanied by rapid climatic adaptation.

Using an analysis of a collection of European native and North American invasive accessions, a recent paper in Molins Annals of Botany examines biogeographic differentiation in both natural and introduced populations, and test whether variation in apomixis traits is correlated with the propensity for H. perforatum to invade novel environments.

 

Molins, M.P., Corral, J.M., Aliyu, O.M., Koch, M.A., Betzin, A., Maron, J.L., & Sharbel, T.F. (2014) Biogeographic variation in genetic variability, apomixis expression and ploidy of St. John’s wort (Hypericum perforatum) across its native and introduced range. Annals of Botany, 113 (3): 417-427 doi: 10.1093/aob/mct268.
St. John’s wort (Hypericum perforatum) is becoming an important model plant system for investigations into ecology, reproductive biology and pharmacology. This study investigates biogeographic variation for population genetic structure and reproduction in its ancestral (European) and introduced (North America) ranges. Over 2000 individuals from 43 localities were analysed for ploidy, microsatellite variation (19 loci) and reproduction (flow cytometric seed screen). Most individuals were tetraploid (93 %), while lower frequencies of hexaploid (6 %), diploid (<1 %) and triploid (<1 %) individuals were also identified. The presence of pure and mixed populations representing all three genetic clusters in North America demonstrates that H. perforatum was introduced multiple times onto the continent, followed by gene flow between the different gene pools. Taken together, the data presented here suggest that plasticity in reproduction has no influence on the invasive potential of H. perforatum.

 

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Tomorrow’s Table by Pamela Ronald and Raoul Adamchak

Tomorrow's Table cover

Quite a few people have recommended this book to me, but I hadn’t made time to read it. My loss, this is an excellent book. I was told it was a good explanation about the uses of Genetic Engineering in farming. It does tackle that, but it also has a much broader vision, also talking about the role of organic farming in the future.

The authors Pamela Ronald and Raoul Adamchak are a husband and wife team. Pamela Ronald talks about genetic engineering, while Raoul Adamchak talks about the teaching he does on UC Santa Cruz’s organic farm. The third feature of the book is the recipes interspersed with the text. The recipes highlight one of the best features of the book, it’s very personal, which makes it very relatable. There is a danger with this in that you risk replacing facts with anecdata: genetic engineering is ok, because it worked for me. Fortunately they authors move from the specific, this is what we do on the farm, to the general, and this is what the science says about how it works.

The book opens with Pamela Ronald’s work with rice. She had been trying to make a breed of rice that can survive flooding. I’ve seen paddy fields and I thought all rice could survive flooding, but you can take it too far. It matters because rice is the staple food in a lot of the world. The climate is becoming more unpredictable and while drought might be a problem in some places, in others there’s a very real danger of catastrophic flooding. Rice can survive some flooding but not weeks.

Pamela Ronald found a gene in another form of rice that could help it survive longer and then used genetic engineering to transfer the gene to a rice people ate. It’s not the popular image of genetic engineering, but it is one that could make a lot of difference.
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This Week in Annals of Botany

Light microscopy images of wood Automatic identification and characterization of radial files in light microscopy images of wood
Analysis of anatomical sections of wood provides important information for understanding the secondary growth and development of plants. This study reports on a new method for the automatic detection and characterization of cell files in wood images obtained by light microscopy.

 

Using virtual 3-D plant architecture to assess fungal pathogen splash dispersal in heterogeneous canopies: a case study with cultivar mixtures and a non-specialized disease causal agent
Recent developments in plant disease management have led to a growing interest in alternative strategies, such as increasing host diversity and decreasing the use of pesticides. Use of cultivar mixtures is one option, allowing the spread of plant epidemics to be slowed down. As dispersal of fungal foliar pathogens over short distances by rain-splash droplets is a major contibutor to the spread of disease, this study focused on modelling the physical mechanisms involved in dispersal of a non-specialized pathogen within heterogeneous canopies of cultivar mixtures, with the aim of optimizing host diversification at the intra-field level.

 

AGO1 controls arabidopsis inflorescence architecture possibly by regulating TFL1 expression
The TERMINAL FLOWER 1 (TFL1) gene is pivotal in the control of inflorescence architecture in arabidopsis. Thus, tfl1 mutants flower early and have a very short inflorescence phase, while TFL1-overexpressing plants have extended vegetative and inflorescence phases, producing many coflorescences. TFL1 is expressed in the shoot meristems, never in the flowers. In the inflorescence apex, TFL1 keeps the floral genes LEAFY (LFY) and APETALA1 (AP1) restricted to the flower, while LFY and AP1 restrict TFL1 to the inflorescence meristem. In spite of the central role of TFL1 in inflorescence architecture, regulation of its expression is poorly understood. This study aims to expand the understanding of inflorescence development by identifying and studying novel TFL1 regulators.

 

Explaining ontogenetic shifts in root-shoot scaling with transient dynamics
Simple models of herbaceous plant growth based on optimal partitioning theory predict, at steady state, an isometric relationship between shoot and root biomass during plant ontogeny, i.e. a constant root–shoot ratio. This prediction has received mixed empirical support, suggesting either that optimal partitioning is too coarse an assumption to model plant biomass allocation, or that additional processes need to be modelled to account for empirical findings within the optimal partitioning framework. In this study, simulations are used to compare quantitatively two potential explanations for observed non-isometric relationships, namely nutrient limitation during the experiments and initial developmental constraints.

 

Callose biosynthesis in arabidopsis with a focus on pathogen response: what we have learned within the last decade
(1,3)-β-Glucan callose is a cell wall polymer that is involved in several fundamental biological processes, ranging from plant development to the response to abiotic and biotic stresses. Despite its importance in maintaining plant integrity and plant defence, knowledge about the regulation of callose biosynthesis at its diverse sites of action within the plant is still limited. Arabidopsis (Arabidopsis thaliana) is one of the best-studied models not only for general plant defence responses but also for the regulation of pathogen-induced callose biosynthesis. This article summarizes what is known about the regulation of callose synthase activity as well as what has been discussed with regard to this topic within the last decade based on results derived from new techniques and available mutant lines, focusing on the progress that has been made in understanding the regulation of callose biosynthesis in response to pathogen attack.

 

Linking ecophysiological modelling with quantitative genetics to support marker-assisted crop design for improved yields of rice under drought stress
Genetic markers can be used in combination with ecophysiological crop models to predict the performance of genotypes. Crop models can estimate the contribution of individual markers to crop performance in given environments. This study explores the use of crop models to design markers and virtual ideotypes for improving yields of rice (Oryza sativa) under drought stress.

 

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Floral volatiles in Ipomopsis hybrids

Floral volatiles in Ipomopsis hybrids

Floral volatiles in Ipomopsis hybrids

Ipomopsis aggregata and I. tenuituba are two sister species that frequently produce natural hybrids. Bischoff et al. study floral scent in parental species and natural hybrids to explore potential scent mediation of prezygotic and postzygotic reproductive isolation. They find that there is qualitative overlap in the floral bouquets, yet the quantitative emission rates differ. A striking difference is the compound indole, emitted almost exclusively by I. tenuituba at night. Emissions by hybrids are highly variable, and not generally intermediate between the parents, although indole emissions are intermediate. The indole signal could potentially serve as a hawkmoth attractant that mediates reproductive isolation both before and after hybrid formation.

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Genome size variation and evolution in allotetraploid Arabidopsis kamchatica and its parental species, A. lyrata and A. halleri

OLYMPUS DIGITAL CAMERAGenome doubling and changes in genome size are fundamental evolutionary processes, with polyploidy being one of the most important forces influencing plant diversification. However, little is currently known about the extent of genome size variation within taxa and the evolutionary forces acting on this variation. Arabidopsis kamchatica has been reported to contain both diploid and tetraploid individuals (2 or 4 copies of every chromosome). In a new study in AoB PLANTS, Wolf et al. found genome size differences among populations, and among populations genome size varied by 7%. However, all sampled A. kamchatica plants from a wide geographic range were tetraploids. This level of intraspecific genome size variation in A. kamchatica is lower than in other Arabidopsis taxa. Due to its close relationship to A. thaliana, A. kamchatica has the potential to be very useful in the study of polyploidy and genome evolution.

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Making waves at the Plant Calcium Signalling Meeting

Calcium ions (Ca2+) are important signal molecules to relay information around, and between cells. In plants, calcium signals are involved in many processes including cell growth, environmental stress (e.g. high salt in soil) responses, and defence against disease-causing microbes. Last week, many of the researchers studying calcium signals in plants gathered together at the Plant Calcium Signalling 2014 meeting in Münster, Germany.

Main administration building of WWU Münster.

Main administration building of WWU Münster. Photo by Rüdiger Wölk / Wikipedia.

I really enjoyed the meeting. It was great to hear about the current research being undertaken by others, and to see how much the research area has moved forward since the previous meeting was held in 2010. Lots of exciting research was presented at the conference, but I’m just going to mention a few of my favourites.

Long-distance calcium waves in plant roots were discussed from the perspective of a biologist (Simon Gilroy, University of Wisconsin), and then a physicist (Matthew J Evans, John Innes Centre). Gilroy’s research group found that treating plant roots with salt (NaCl) activates rapid calcium (Ca2+) waves that travel at speeds of around 400 µm/s from root to shoot (1). High salt levels can be harmful to plants and the calcium wave is likely to be involved in activation of whole-plant stress responses that help the plant survive in these conditions. In the video below the wave is visible as a colour change from yellow (low calcium ion levels) to red (high calcium ion levels).

Evans then presented the mathematical model he is developing based on Gilroy’s biological data. Although the model is a simplification of what would be happening in a plant, it matches the current biological data pretty well. Using the model, it is possible to make predictions that Gilroy’s research group can now test in plants.

Calcium signals are sensed by calcium-binding proteins that then activate/inactivate downstream responses in cells. There are loads of calcium-binding proteins in plants, grouped into several types. Why plants need so many calcium-binding proteins is a bit of a mystery. At the meeting, Jürg Kudla (WWU Münster, Germany) presented data that may help to answer this question. He found that two calcium-binding proteins from different families act synergistically to activate a downstream cell response. Although both proteins could activate the response on their own, a much higher level of activation was achieved when both were present.

Researchers have access to several tools to visualise calcium signals in cells. Melanie Krebs (University of Heidelberg) discussed her work adapting the GECO calcium sensors, which were first developed for use in animal cells (2), for expression in various locations within plant cells. The GECOs are more sensitive than other calcium reporters such as Cameleon YC3.6. Krebs demonstrated that they could be used to visualise some calcium changes in individual cells that have only previously been observed at the whole plant/organ level.

My two other favourite talks were about the roles of calcium in plant development. José Feijo (University of Maryland) discussed the role of calcium in pollen tube growth during fertilisation. Straight after, Alex Webb (University of Cambridge) presented his research on the role of calcium in the circadian clock, which is the internal clock plants have to co-ordinate their growth and metabolism with the day-night cycle. Alongside all the talks, the conference had poster sessions where researchers could discuss their work on a more informal basis.

The meeting was a really useful opportunity for the plant calcium signalling research community to get together and I would like to thank the organising committee for all the hard work they put into running it.

References

1) Choi et al (2014) Salt stress-induced Ca2+ waves are associated with rapid, long-distance root-to-shoot signalling in plants. PNAS. PMID: 24706854
2) Zhao et al (2013) An Expanded Palette of Genetically Encoded Ca2+ Indicators. PubMed Central. PMID: 21903779

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