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Posts Tagged ‘ecology’

Anthers pollenEscape of the Transgenes?

Last week, I was a bit startled as I listened to a podcast of NPR’s Science Friday program.

In this episode (2/18/2011), host Ira Flatow was interviewing the new president of the American Association for the Advancement of Science (AAAS) Dr. Nina Fedoroff (a distinguished plant molecular biologist, by the way).

She shocked me (and, apparently, Ira Flatow) by flatly denying that there were any cases of transgenes “leaking” into the environment from genetically-engineered (GE) crop plants.

To Ira’s credit, he challenged her on this somewhat preposterous statement. (See below why it was indeed such a surprising remark.)

Because this episode elicited a “storm” of letters and e-mails, Ira Flatow did a follow-up interview (which you can listen to here) with Fedoroff and plant ecologist Dr. Allison Snow.

Briefly, Dr. Snow provided several examples of transgenes being acquired by wild relatives of genetically engineered crop plants, particularly canola. Dr. Fedoroff seemed to dismiss these examples as merely “management” problems.

It’s Hard To Corral A Transgene In The Wild.

Contrary to Dr. Fedoroff’s statement on Science Friday, there is ample evidence that transgenes have “leaked” from GE crops to other plants.

Escape plantFor example, in a previous post regarding the herbicide Roundup® (glyphosate), I noted how a transgene conferring resistance to Roundup® had escaped from a test plot of genetically-engineered turfgrass to adjacent populations of a related native grass.

There certainly are other published examples (see ref. 1, e.g.) of gene flow from GE crops to other non-GE crops and to weedy or wild relatives. And, as genetically-engineered organisms (GEOs), such as crop plants, proliferate, there will likely be more.

It’s not hard to imagine the ecological and agricultural implications if so-called “weedy” plants acquire transgenes conferring herbicide tolerance and pest resistance, for example, from related GE crop species.

But, although gene flow from GE plants to wild relatives has been well documented, the ecological significance of these occurrences is much less well understood.

Overall, there are relatively few data available with which to evaluate the potential for increased weediness or invasiveness in a crop species with fitness-enhancing abiotic and biotic GM traits. A better understanding is needed of the factors that presently control population size and range limits of either the crop volunteers or wild recipient populations, and the degree that survival or reproduction in the field is presently affected by the relevant biotic or abiotic stress-tolerance trait.” – from Ref. 1 below.

In a sense, Dr. Fedoroff is correct in stating that this is a “management” issue. But perhaps such management of GE crops should be conducted primarily by plant ecologists, such as Dr. Snow (see ref. 2, e.g.), rather than by plant genetic engineers.

Re. DIY Biotechnologists: This is certainly one of the serious drawbacks of GEOs that all of you DIY genetic engineers must seriously consider before releasing your creations into the wild.

References

1. Warwick, S.I., H.J. Beckie and L.M. Hall (2009) “Gene Flow, Invasiveness, and Ecological Impact of Genetically Modified Crops”, Annals of the New York Academy of Sciences, Vol. 1168, pp. 72–99. (PDF)

2. Snow, Allison A. (2010) “Risks of Environmental Releases of Synthetic GEOs”, Invited Presentation for the Presidential Commission for the Study of Bioethical Issues, July 8, 2010 (PDF) The agenda and video of this meeting are available here.

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ethylene_T.jpgC’est un gaz. Es un gas. Es ist ein gas. It’s a Gas!

If you are familiar with the gaseous plant hormone ethylene, it’s most likely because of its ability to promote fruit ripening in apples, bananas, tomatoes, etc..

Ethylene also affects many other aspects of a plant’s life cycle, including seed germination, growth and development, responses to physical and biological stress, leaf abscission, and senescence.

It may even be responsible for how some herbicides kill plants.

But how does ethylene work?

That is, how can this simple gas (CH2-CH2) mediate so many different processes in plants? Where and how is this chemical signal produced in plants? And how is this signal received by plant cells and then amplified into the responses we observe?

Making the Signalethylene_T2.jpg

Virtually all the cells in a plant have the potential to make ethylene. Plant cells make ethylene starting from the amino acid methionine (see below).

And it turns out that during the course of a plant’s life – from seed germination to senescence – ethylene may be made not only as part of the developmental program of the plant, but also in response to random events, such as wounding and pathogen attack.

The primary way plants (at least Arabidopsis) regulate the amount of ethylene is through the expression of a family of genes that encode enzymes (the ACS protein family) that catalyze the synthesis of the key metabolic precursor to ethylene, namely, ACC*.

Methionine –> SAM* –ACS proteins –> ACC* + O2 –> Ethylene
* SAM = S-Adenosyl-L-Methionine, ACC = 1-AmminoCyclopropane-Carboxylate

(Please see here for diagram of ethylene biosynthetic pathway in plants.)

Quoting part of a recent report (ref. 1 below) on the genetics of ethylene biosynthesis:

“We view the ACS protein family as a “Symphony Orchestra” (45-member when all nine genes are expressed in a cell) that regulates ethylene-mediated processes by generating appropriate amounts of ACC in the proper spatial and temporal manner through their harmonious interplay. At any given moment, the orchestra is tuned by various inducers to produce ACC sufficient to mediate myriad ethylene responses…”

orchestra.jpg


So, this may explain why the biosynthesis of ethylene in plants can be affected by so many different factors.

Next-time: The Ripe Stuff – Part 3: How Plants Respond to Ethylene

References:

1. Tsuchisaka, A., et al. (November 2009) “A Combinatorial Interplay Among the 1-Aminocyclopropane-1-Carboxylate Isoforms Regulates Ethylene Biosynthesis in Arabidopsis thaliana.” Genetics vol. 183, pp. 979-1003. (PDF)

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big_leaf.jpgLeaf Surfaces = Microbial Habitats

Imagine all the leaves of all the plants currently living on planet Earth.

Now, add up all the surface areas of all of those leaves.

And your answer is?… No idea?….

Luckily, some microbiologists have made an estimate, and it’s an astounding number.

According to a current review (see ref 1 below), the terrestrial leaf surface area that might be colonized by microbes is approximately 640,000,000 square kilometers or about 250 million square miles! (For perspective, consider that the total surface area of the Earth is 197 million square miles.)

From this, microbiologists have estimated that the planetary leaf-surface bacterial population on Earth may be as large as 1026 cells! (Yes, that’s the numeral 1 with 26 zeros behind it.)

“Clearly, in aggregate, these bacteria are sufficiently numerous to contribute in many processes of importance to global processes, as well as to the behavior of the individual plants on which they live.”-(from ref 1 below).

In other words, the bacteria that live on the leaf surface are so numerous that they not only likely affect the plant on which they dwell but, collectively – on a planetary scale – they are so numerous as to significantly affect the global carbon and nitrogen cycles on Earth.

The Phyllosphereleaf_droplets.jpg

The term “phyllosphere” was first published by Dr. Jakoba Ruinen in 1961 (see ref 2 below), who studied tropical ecology beginning in the 1950’s. She called the interface between leaves and air the “phyllosphere”, and said that this was a much neglected milieu, compared to studies of the rhizosphere.

“Under the microscope, aerial plant leaves resemble eerie landscapes, with deep gorges, tall peaks and gaping pits that riddle the waxy surface. [e.g., see photo below] Add to this scenery a climate that features temperature highs of 50 °C [122 °F] or more, exposure to harmful ultraviolet rays, erratic periods of drought and limited access to nutrients, and one gets the picture that this is a hostile environment. Still, many bacteria, fungi, yeast and other microorganisms dwell in great abundance in this ‘phyllosphere’…” (from ref 3 below).

leaf_surface.jpgWho Lives in the Phyllosphere?

“The microbial communities of leaves are diverse and include many different genera of bacteria, filamentous fungi, yeasts, algae, and, less frequently, protozoa and nematodes.” (from ref 1 below)

Most of what we know about these leaf “epiphytes” come from culturing (or trying to culture) representative isolates in the lab.

In a recent report (ref 4 below), the investigators have taken a 21st-century approach to the question: “What bacteria live in the phyllosphere?”.

Using a new “metaproteogenomic” approach, they analyzed the bacteria associated with leaves of field-grown soybean and clover plants and wild populations of Arabidopsis thaliana plants. (This technique is related to proteogenomics.)

This study not only revealed “who” was there, but also provided clues to how such bacteria survive in the phyllosphere. Briefly, they discovered “…a high consistency of the communities on the 3 different plant species, both with respect to the predominant community members…” and with respect to the proteins that these bacteria apparently use to survive such a relatively hostile environment.

Photo Credit: Top two photos above by Koolpix/ Jay D., who has been awarded the Nature Photo of the Week by the Nature Conservancy. Twice! (please see here and here). Congratulations! And thank you!

Bottom Line: Using new molecular biology techniques, scientists have discovered important new information regarding not only what bacteria live in the phyllosphere but also how they do it.

References

1. Lindow, S. and Brandl, M.T. (2006) “Microbiology of the Phyllosphere”, Applied and Environmental Microbiology vol. 69, pp. 1875-1883. (full text)

2. Ruinen, J. (1961) “The Phylloshere. I. An Ecologically Neglected Mileau”, Plant and Soil vol. 15, pp. 81-106. (preview PDF)

3. Leveau, J. (2009) “Life on leaves.” Nature vol. 461, p. 741. (Abstract)

4. Delmotte, N., et al. (2009) “Community proteogenomics reveals insights into the physiology of phyllosphere bacteria” Proceedings of the National Academy of Sciences (USA) vol. 106, pp. 16428-16433. (full text).

HowPlantsWork © 2008-2011 All Rights Reserved.

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rice.jpgWhat do a fungal disease of rice, dwarf plants, flowering, and beer have in common?

Answer: They all may involve the action of the plant hormone gibberellin, a.k.a. gibberellic acid (GA).

Let me explain…..

This plant hormone was first discovered by Japanese scientists working on a rice disease called bakanae caused by the fungus Gibberella fujikuroi. (And now you see how the hormone got its name.) The fungus infects rice and produces GA as a metabolic byproduct. This is too much GA for the rice, which causes the plants to grow too tall and spindly. The plants are eventually blown over by the wind and die. The fungus dines on the remains.

Many dwarf plants produce too little GA, typically because of a mutation in a gene that codes for an enzyme involved in GA biosynthesis.

Gibberellins have long been implicated in stimulating the bolting (rapid stem elongation) and flowering in rosette plants, though it’s still unclear exactly how GA’s work in different plant families (more on this at another time).

Guinness.jpgBeer? Well, stick with me here…. Malted barley is a key ingredient in most beers. Malting (starch into sugars) is the result of the spouting (germination) of the cereal grains. And GA stimulates germination in the seeds of some plant species, particularly barley.

Thus, gibberellins mediate many aspects of plant development – from seed germination to stem elongation to flowering – all of which will likely be affected by climate change. Understanding how GA’s work in plants may help us ameliorate some of the effects of such environmental changes.

How do plants adjust their development and physiology in response to environmental conditions?

Plant response to the environment can usually be divided into three consecutive steps: perception –> signal –> response.

That is, land plants must first perceive the environmental conditions. They then use hormonal signals to elicit appropriate biological responses. Some responses affected by gibberellins include: seed dormancy/germination, plant height, and flowering.

Indeed, gibberellins have been theorized to be critical in how early land plants learned to respond to changing environments.

Array.jpgHow do gibberellins work?

A fundamental step in understanding how a signal works is identifying what specifically receives the signal.

Hence, much effort has been devoted to identifying and characterizing plant hormone receptors.

Recent evidence supports the idea that GA works by triggering the elimination of proteins -called DELLA proteins – that inhibit plant growth.

It turns out that these DELLA proteins may be important for the integration of plant responses to the environment.

Last week two reports in the journal Nature further refined our knowledge of GA receptors proteins.

Bottom Line: Because gibberellins play a central role in plant responses to the environment, understanding how they work only enhances our ability to cope with problems – both ecological and agricultural – that may result from climate change.

HowPlantsWork © 2008-2011 All Rights Reserved.

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