Tag Archives: angiosperms

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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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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Highlight on diversity, ecology and evolution of extrafloral nectaries

Highlight on diversity, ecology and evolution of extrafloral nectaries

Highlight on diversity, ecology and evolution of extrafloral nectaries

Plants in over 100 families bear extrafloral nectaries (EFNs), which secrete a carbohydrate-rich food that attracts ants and other arthropods. By fostering ecologically important protective mutualisms, EFNs play a significant role in structuring both plant and animal communities. As an introduction to a Highlight collection of papers published in the June issue, Marazzi et al. provide an overview of recent research on EFN diversity, ecology and evolution, and conclude that our understanding of the roles EFNs play in plant biology is being revolutionized with the use of new tools from developmental biology and genomics, new modes of analysis allowing hypothesis-testing in large-scale phylogenetic frameworks, and new levels of inquiry extending to community-scale interaction networks. The authors highlight major gaps in our current knowledge, and outline directions for future research.

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Highlight on diversity, ecology and evolution of extrafloral nectaries

Highlight on diversity, ecology and evolution of extrafloral nectaries

Highlight on diversity, ecology and evolution of extrafloral nectaries

Plants in over 100 families bear extrafloral nectaries (EFNs), which secrete a carbohydrate-rich food that attracts ants and other arthropods. By fostering ecologically important protective mutualisms, EFNs play a significant role in structuring both plant and animal communities. As an introduction to a Highlight collection of papers published in the June issue, Marazzi et al. provide an overview of recent research on EFN diversity, ecology and evolution, and conclude that our understanding of the roles EFNs play in plant biology is being revolutionized with the use of new tools from developmental biology and genomics, new modes of analysis allowing hypothesis-testing in large-scale phylogenetic frameworks, and new levels of inquiry extending to community-scale interaction networks. The authors highlight major gaps in our current knowledge, and outline directions for future research.

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Fire

Image: Wikimedia Commons.

Image: Wikimedia Commons.

Picking up on my elemental theme, fire has long been considered a major influence on evolution of the angiosperms, whether natural or anthropogenic conflagrations. This incendiary interaction has not been helped by plants themselves, which not only generate highly calorific and combustible dry matter but also provide the oxygen needed to permit their combustion. The dramatic effect of fire on vegetation was graphically demonstrated in the Australian wildfires in January. Although fire has been an abiotic factor for hundreds of millions of years, the origins of so-called ‘fire prone’ floras have hitherto been considered to be comparatively recent phenomena. However, using a molecular-dated phylogeny for the Proteaceae, a ‘great Gondwanan family with a 113-million-year evolutionary history’, Byron Lamont and Tianhua He have established that angiosperm fire proneness can now be traced back 83–94 million years into the ‘fiery Cretaceous’. Furthermore, the associated evolution of on-plant (serotiny; in which seed release occurs in response to an environmental trigger, e.g. fire) and soil seed storage, and – evolutionarily – more recent ant-dispersal characteristics, affirms those behaviours as ancient adaptations to fire among flowering plants. Interestingly, and by way of setting up some sort of competition between angio- and gymnosperm, Tianhua He et al. have previously suggested a 126-million-year evolutionary history of fire-adapted traits in the Pinaceae. And if you want more on the evolutionary supremacy tussle between those great seed-bearing phyla, then I can recommend Clément Coiffard et al.’s paper that proposes a window of opportunity of approximately 145–66 million years ago (the Cretaceous Period) during which angiosperms rose to dominance over the gymnosperms – and all other members of the Plant Kingdom.

[A video blog on the Proteaceae can be found elsewhere on this site – Ed.]

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DNA content for 407 plant species from the USA

DNA content for 407 plant species from the USA

DNA content for 407 plant species from the USA

The genome sizes of plants represent a key character often associated with other traits. Bai et al. use flow cytometry to provide prime C-values for 514 taxa. Most of these (407) are new reports, including 129 genera and five families extending over 390 angiosperms, two gymnosperms, ten monilophytes and five lycophytes. New family C-value maxima or minima are reported for Betulaceae, Ericaceae, Ranunculaceae and Sapindaceae. These data provide the basis to explore phylogenetic patterns of C-value variation and relationships between genome size and other functional traits with the goal of linking genome size variation to other patterns of diversity and drivers of ecological change.

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Evolution of AGPase duplicates

Evolution of AGPase duplicates

Evolution of AGPase duplicates

ADP-glucose pyrophosphorylase (AGPase), a key enzyme in starch biosynthesis, is comprised of large (LSU) and small (SSU) sub-units encoded by multiple paralogous genes in angiosperms. Corbi et al. investigate the patterns of molecular evolution of AGPase genes following duplications. They find that both coevolution among amino acid residues located in between-sub-unit interaction domains or within the highly constrained SSU, and repeated subfunctionalization events under the ‘Escape from Adaptive Conflict’ model have contributed to AGPase evolution.

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Love and Flowers: When analogies break down

I’ve learned a lot from a new article in AoB PLANTS, the Open Access sister Journal to Annals of Botany. It’s Green love talks; Cell-cell communication during double-fertilization in flowering plants by Tomokazu Kawashima and Frederic Berger and it shows how things get really interesting when simple analogies break down. The paper is a review of recent research on cell signalling and how it works to ensure successful fertilisation of flowers by pollen. Borrowing from the title, it’d be easy to try and conjure up a start like: “Experts have got it right, the key to a successful relationship is communication.” But Kawashima and Berger show that there are times when anthropomorphising plants can effectively hide what is so fascinating about them.

Couple holding hands

This post would have been a lot easier to write if plant communication was simply about holding hands. Photo by Rachel Davies.

The issue is how does signalling work to get the male material into the female reproductive cells to start the seed making process? I’ve had the talk, so I know that it’s a matter of delivering sperm to the egg, so it’s just a case of making sure that the female organs signal they’re receptive, yes? In the case of angiosperms, flowering plants, it’s more complex. You need two male gametes to fertilise two parts of the female. There’s a central cell and within that there’s an egg cell.

This has been source of a puzzle for plant scientists. There are two female cells, so presumably there are two male cells, yet they’re coming from the same source i.e. a pollen grain that’s landed on the stigma and germinated there. How does the plant stop the wrong male cell getting to the wrong female one?

The answer found from studies of flowers, including Arabidopsis thaliana, is a surprise. They’re not two types of male cell. As the authors report, advances in high resolution imaging mean that they can identify that the two male cells are identical. All the hard work seems to be done by the female parts of the plant. Cells surrounding the egg cell produce proteins to attract the pollen tubes, and signalling between the female cells makes sure everything is delivered to the right place.

To be honest, some of the language in the paper is daunting. Being a human I’m used to the idea that plants are passive. No doubt, Kawashima and Berger would emphatically disagree. There’s a lot going on in a pollinated flower and the uses of various terms and proteins can be dizzying. What they show is that the signalling is complex. When you think about the scale of the operations it’s hard to see how so many proteins can be shuffled, ordered and directed to make everything happen. Far from silence, it looks like there’s a well-orchestrated chemical symphony being played in the cells that makes the double-fertilization possible. Keeping on top of all the detail means that the paper is not light-reading. It can however be rewarding reading.

The best papers don’t simply answer questions, they also open up new avenues of research. Here Kawashima and Berger are extremely helpful. If you’re looking for something to research in signalling then the authors have erected big signposts in the conclusion with big arrows marked ‘mysteries this way’. If you’re looking for a departure point into cell-cell signalling, then this looks like a helpful guide to where the interesting puzzles in mechanisms are.

Photo: Holding Hands by Rachel Davies. Licenced under a Creative Commons BY licence.

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