Hydrochoric gene flow in invasive riparian Impatiens

Hydrochoric gene flow in invasive riparian Impatiens

Hydrochoric gene flow in invasive riparian Impatiens

Riparian systems are prone to invasion by alien plant species, which may be facilitated by hydrochory, the transport of seeds by water. Love et al. study gene flow associated with hydrochoric dispersal of the invasive riparian plant Impatiens glandulifera (Himalayan balsam) in two contrasting river systems and find a significant increase in levels of genetic diversity downstream, consistent with the accumulation of propagules from upstream source populations. There is strong evidence for organisation of this diversity between different tributaries, reflecting the dendritic organisation of the river systems studied. The results indicate that hydrochory, rather than anthropogenic dispersal, is primarily responsible for the spread of I. glandulifera in these river systems.

 

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Caught in the act…

Image: Marie Majaura/Wikimedia Commons.

Image: Marie Majaura/Wikimedia Commons.

Examples abound of ancient life forms trapped in suspended inanimation within amber (fossilised tree resin) and which give us clues about ancient – maybe even extinct – biota and their ecology (e.g. ‘The past is bright, the past is … amber’). A revelation concerning amber-encased plant material suggests that current sexual reproduction in angiosperms may have remained little changed in over 100 million years.

This insight comes from a new, albeit extinct, species named Micropetasos burmensis and work by George Poinar et al. with amber deposits from the mid-Cretaceous in Burma (Republic of the Union of Myanmar). Although given a binomial (with a formal description in English, as now permitted) and clearly a flowering plant, the team ‘prefer to leave the question of its exact familial relationships open at this time’. However, arguably the most interesting aspect of this discovery is the sight of pollen tubes growing out of two grains of pollen and penetrating the flower’s stigma (the receptive part of the female reproductive system). This precedes fertilisation of the egg, which would have begun the process of seed formation, had this act of plant coitus not been interrupted.

Curiously, this is not mentioned explicitly in the journal article, but was only discerned in the press release promoting it). Was that statement too outrageous or speculative for inclusion in the journal article? Surely not; legitimate commentary such as this ought to be encouraged, and only serves to make the discovery even more interesting. Come on, lads, don’t hide your light under a bush(-el)

[OK, you can relax, I’ve saved you the trouble of finding that story about 165-million-year-old fossil insects caught during copulation. Text – and pictures – at the Smithsonian’s website. – Ed.]

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Another bacterial trick to manipulate plant hormone-mediated responses

Another bacterial trick to manipulate host hormone-mediated response Pseudomonas syringae is a widespread bacterial pathogen that causes disease on a broad range of economically important plant species. In order to infect, P. syringae produces a number of toxins and uses a type III secretion system to deliver effector proteins into eukaryotic cells. This mechanism is essential for successful infection by both plant- and animal-associated bacteria as bacterial mutants are no longer pathogenic. However, the molecular function and host targets of the vast majority of effectors remain largely unknown.

Plant immunity relies on a complex network of small-molecule hormone signaling pathways (see: Wasternack, C. (2007) Jasmonates: an update on biosynthesis, signal transduction and action in plant stress response, growth and development. Annals of botany, 100(4), 681-697). Classically, salicylic acid (SA) signaling mediates resistance against biotrophic and hemi-biotrophic microbes such as P. syringae, whereas a combination of jasmonic acid (JA) and ethylene (ET) pathways activates resistance against necrotrophs such as the fungus Botrytis cinerea. SA and JA/ET defense pathways generally antagonize each other – elevated resistance against biotrophs is often correlated with increased susceptibility to necrotrophs and vice versa. The collective contribution of these two hormones during plant-pathogen interactions is crucial to the success of the interaction. Remarkably, some Pseudomonas strains have evolved a sophisticated strategy for manipulating hormonal balance by producing the toxin coronatine (COR), which mimics the plant hormone jasmonate-isoleucine (JA-Ile). The JA-Ile pathway plays a key role in plant immunity by activating defenses against fungal pathogens, while promoting bacterial growth by inhibiting the salicylic acid (SA)-dependent defenses required for Pseudomonas resistance.

A recent paper in PLOS Biology reports that the effector HopX1 from a Pseudomonas syringae strain that does not produce COR exploits an alternative evolutionary strategy to activate the JA-Ile pathway. HopX1 encodes a cysteine protease that interacts with and promotes the degradation of key JA pathway repressors, the JAZ proteins. Correspondingly, ectopically expressing HopX1 in the model plant Arabidopsis induces the expression of JA-dependent genes, and natural infection with Pseudomonas producing HopX1 promotes bacterial growth in a similar fashion to COR. These results highlight a novel example by which a bacterial effector directly manipulates core regulators of hormone signaling to facilitate infection:

Gimenez-Ibanez S, Boter M, Fernández-Barbero G, Chini A, Rathjen JP, et al. (2014) The Bacterial Effector HopX1 Targets JAZ Transcriptional Repressors to Activate Jasmonate Signaling and Promote Infection in Arabidopsis. PLoS Biol 12(2): e1001792. doi:10.1371/journal.pbio.1001792

 

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Erotic Botany wins National Poetry Competition

Botany is sexy. To prove it, Bernard and Cerinthe by Linda France has won the National Poetry Competition in the UK.

Cerinthe major Purpurascens

Cerinthe major ‘Purpurascens’ by gnomicscience / Flickr. CC BY-NC.

The Guardian reports the poet saying:

It was the end of August and there was a plant I’d never seen before – Cerinthe major Purpurascens – and I was just astonished by it. It’s a very intense blue and the leaves are a silvery green … they’re quite thick, almost waxy, fleshy. That’s one of the things I’m drawn to about plants – they express this tremendous ‘otherness’, but they just stay there and let you respond to them, unlike a bird or animal that disappears. A plant remains for you to give your attention to.

You can read the poem, or hear Linda France recite it at the National Poetry Society’s page.

You can also read more about her work at Botanical: Poetry and Plants.

Image

Cerinthe major ‘Purpurascens’ by gnomicscience / Flickr. This image licensed under a Creative Commons by-nc licence.

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How environmental stress from transplanting into foreign habitats influences inbreeding depression

Inbreeding depression can lower individual fitness and cause the extinction of populations. As a result, it is of interest to evolutionary biologists and conservationists alike. Studies have shown that inbreeding depression can increase in stressful environments. However, most of these studies do not utilize natural environmental stress. In a recent article published in AoB PLANTS, Hereford tested how natural environmental stress from transplanting into foreign habitats influences inbreeding depression. While there was significant inbreeding depression, there was no difference in inbreeding depression between plants in their native environment versus foreign habitats. These results imply that inbreeding depression does not increase when environmental stress reflects natural variation.

The image shows a flower of Diodia teres along with Inland (left) and Dunes (right) habitats.

The image shows a flower of Diodia teres along with Inland (left) and Dunes (right) habitats.

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Evolutionary history of Afro-Madagascan Ixora

Ixora regalis

Ixora regalis

The pantropical genus Ixora is one of the largest genera in Rubiaceae, with approximately 530 species. Tosh et al. conduct phylogenetic analyses based on four plastid and two nuclear ribosomal markers to infer the historical biogeography of Afro-Madagascan Ixora species. They find that Madagascan Ixora do not form a monophyletic group, but are represented by two separate lineages of different ages, with at least one dispersal event occurring from East Africa into Madagascar in the late Pliocene. Both lineages of Madagascan Ixora exhibit morphological characters that are rare throughout the rest of the genus, including pauciflorous inflorescences and extreme corolla tube length.

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Biomechanics of aquatic plants under aerial conditions

Biomechanics of aquatic plants under aerial conditions

Biomechanics of aquatic plants under aerial conditions

Terrestrial plants don’t like being underwater for long periods of time – as farmers across the UK have found out to their cost in the past few months. But aquatic plants are not designed to “work” out of the water either. Normally, the aquatic environment supports much of the weight of the plant and consequently, aquatic plants don’t devote as much of their resources to the sort of structural tissues required to hold up land plants.

But what about plants from environments where the water level routinely fluctuates? Wetlands are impacted by hydrological regimes that can lead to periods of low water levels. During these periods, aquatic plants experience a drastic change in the mechanical conditions that they encounter, from low gravitational and tensile hydrodynamic forces when exposed to flow under aquatic conditions, to high gravitational and bending forces under terrestrial conditions. The objective of this study was to test the capacity of aquatic plants to produce self-supporting growth forms when growing under aerial conditions by assessing their resistance to terrestrial mechanical conditions and the associated morpho-anatomical changes.

A recent paper in Annals of Botany investigates the capacity of aquatic plants from eight genera to produce self-supportive phenotypes capable of resisting terrestrial mechanical conditions.

They find that six species show higher stiffness in bending, either as the result of an increased allocation to strengthening tissues or by an increase in cross-sectional area in the organs bearing the mechanical forces. These plastic responses may play a key role in the ability of the species to colonize highly fluctuating environments, but reduced capacity for plants to tolerate aquatic mechanical conditions when water level rises again could represent a cost of producing a growth form adapted to aerial conditions.

Hamann, E., & Puijalon, S. (2013). Biomechanical responses of aquatic plants to aerial conditions. Annals of botany, 112(9), 1869-1878.

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Science: for the sheer fun of it!

Image: Robert Hooke, 1665. Micrographia. Jo. Martyn and Ja. Allestry, London.

Image: Robert Hooke, 1665. Micrographia. Jo. Martyn and Ja. Allestry, London.

Despite frequently expressed assumptions to the contrary, science – whether it’s botany or some lesser intellectual pursuit – isn’t always about having an idea and undertaking an experiment to test it. Anyway, that type of investigation can be hard work. Fortunately, there is an alternative approach that basically studies ‘what’s there’ and muses on why that might be (or not…), so-called blue skies research.  Sadly, the latter type of science – which I think is much more fun and interesting – is less likely to get financed than the ‘there’s a definite question that we aim to answer’ type of study, and is generally much less common. Nice then to see that, in conversation with Sarah Williams in the Howard Hughes’ Medical Institute’s Fall 2013 issue of the HHMI BulletinDr Richard Flavell (Sterling Professor of Immunobiology at Yale School of Medicine) promotes the view that observation-driven studies have a place in science. He goes further in saying that, ‘there’s nothing wrong with a lab team doing observational study after observational study. They are still helping advance the science, and likely providing fodder for hypothesis-driven studies to come…’. Now that is my kind of science. I do hope those who fund research are listening to – and heeding – this!

Unfortunately, I suspect the more usual reaction to requests to finance such work from the grant-awarding bodies would be similar to that which prompted this acknowledgement in a scientific paper: ‘I thank the National Science Foundation for regularly rejecting my (honest) grant applications for work on real organisms (cf. Szent-Gyorgyi, 1972)…’ (from Leigh Van Valen’s* paper, ‘A new Evolutionary Law’). But occasionally studies along the lines of ‘let’s just see what turns up’ do appear. Take, for example, Michael Proctor and Margaret Bradshaw’s first in a planned series of papers on scanning electron microscopy (SEM) examination of leaves of British sedges in New Journal of Botany**. Acknowledging that the ability to identify sedges in the field is important to many vegetation studies but recognising that inflorescences are available for only a short period each year, the pair have concentrated on SEM studies of leaf surfaces to assist those identification endeavours. Whilst the duo don’t advocate taking a SEM into the field, they do believe that such SEM studies will be ‘useful in putting leaf characters on a firmer footing, and drawing attention to characters which could be useful for identification with a hand-lens or low power microscope’ (which can be taken into the field…). The images need to be seen to be properly appreciated, but the imaging of epicuticular waxes in, for example, Figure 1f attests to their high quality. Bring on Part 2!

[For those expecting to read about ‘botanist’ Richard Flavell PhD, FRS, CBE, former Director of the John Innes Centre, etc, I’m sorry to ‘disappoint’ – Ed.]

* Leigh van Valen is an American evolutionary biologist probably best known for the Red Queen Hypothesis.

** this is the official organ of the BSBI,  the leading society in Britain and Ireland for the study of plant distribution and taxonomy. The Botanical Society of Britain and Ireland was formerly called the Botanical Society of the British Isles, and represents a name change every bit as slick as that of the WWF (which changed from World Wildlife Fund to World Wide Fund for Nature in 1986), and which also allows it to keep its abbreviation of BSBI (which is an initialism not an acronym) the same. The New Journal of Botany is itself the successor to the BSBI’s Watsonia journal, named in honour of Hewett Cottrell Watson (one of the “most colourful figures in the annals of British botany”) who developed the vice-county system in 1852 that currently divides up the United Kingdom and the Republic of Ireland into 152 geographical units for vegetation recording purposes.]

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Abscisic acid underlies genotypic variation in stomatal responses

Abscisic acid underlies genotypic variation in stomatal responses

Abscisic acid underlies genotypic variation in stomatal responses

Stomata formed at high relative humidity (RH) are less responsive to abscisic acid (ABA), an effect that varies widely between genotypes. Giday et al. study four rose cultivars (Rosa hybrida) grown at 60% and 90% RH and find stomatal responsiveness to desiccation and ABA feeding to be attenuated in two of them at high RH. [ABA] is lower in plants grown at high RH, an effect that is more pronounced in these sensitive cultivars. They determine that the sensitive cultivars undergo a larger decrease in [ABA], rather than having a higher [ABA] threshold for inducing stomatal functioning. However, the cultivar differences in stomatal closure following ABA feeding are not apparent in response to H2O2 and downstream elements, indicating that signalling events prior to H2O2 generation are involved in the observed genotypic variation.

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