The fruit-fly and the cactus
Aesop (slave and story-teller believed to have lived in ancient Greece, 620–560 bc; http://en.wikipedia.org/wiki/Aesop%27s_Fables) is credited with many fables that delivered morality tales, etc. But one you won't find amongst his collection is ‘the fruit-fly and the cactus’. However, this modern-day cautionary tale has a ‘take home message’ (THM) that would not be out of place alongside his ‘The woman and the fat hen’ (whose THM apparently is that ‘relying on statistics does not always produce results’, or ‘figures are not always facts’; http://www.amazon.com/Aesops-Fables-Signet-Classics-Aesop/dp/0451525655). Anyway, back to the modern-day. We've probably got so used to fruit-flies (‘the arabidopsis of the animal biology world’) being lab-based model organisms (http://en.wikipedia.org/wiki/Model_organisms) that we may be surprised to hear that they do actually live outside of the research facility in the wild. And there are many different species too – not just Drosophila melanogaster (http://en.wikipedia.org/wiki/Drosophila). And some of them are really ‘unusual’ (botanist's speak for ‘really rather interesting, if in a non-plant way’…). Take for instance D. pachea, which is wholly dependent upon the senita cactus (Lophocereus schottii) in the Sonoran Desert (South-western USA/Northern Mexico; http://en.wikipedia.org/wiki/Sonoran_Desert). Why is it so fussy? Work by Michael Lang et al. (Science 337: 1658–1661, 2012) shows that the fly is unable to transform cholesterol into 7-dehydrocholesterol – an important reaction in the usual biosynthetic pathway to the insect hormone ecdysone, which permits the fly's maturation (http://en.wikipedia.org/wiki/Ecdysone) – which is generally a bad thing. However, the fly is able to use cactus-produced lathosterol in place of cholesterol. Thus, the mutation of the fly's appropriately named Neverland enzyme – which deprives it of the ability to transform cholesterol and thus its ability ‘to grow up’ (http://en.wikipedia.org/wiki/Neverland) – has firmly tied the fly's fortunes to those of the cactus. Fortuitously, the fly also has resistance to the otherwise toxic compounds of the cactus (which, the study's authors speculate, may actually have been the first step along the road to its ultimate obligate specialist status as this enabled it to escape competition from other fly species). If you're wondering what the cactus may get out of this, Virginie Orgogozo (last-named author of the Science study) says, ‘D. pachea flies live on rotten parts of the senita cactus. We don't know if there is any benefit for the cactus to host these flies’ (http://blogs.discovermagazine.com/notrocketscience/2012/09/28/). But maybe removal of rotten parts of the plant by the fly lessens the chances of microbial infection of the cactus? Anyway, in its own microcosmic way – and in a satisfying nod in Aesop's direction – this study demonstrates a universal truth: animal fortunes on this rock we call home are intimately bound up with those of plants (and survival of both is probably contingent upon survival of each).
Image: Tomas Castelazo/Wikimedia Commons.
Tentacular spectacular
All plants are fascinating, but some are more fascinating than others (to misquote George Orwell, English novelist and journalist; http://www.quotationspage.com/quote/122.html). And what is more fascinating than a new insight into the world of the carnivorous plant, such as that provided by Simon Popping and colleagues (PLoS ONE 7: e45735, 2012)? Despite appearances to the contrary, not all of those bejewelled, dew-dropped, sun-light-catching tentacles within the glistening ‘disc of death’ that frequently typifies the insect-trapping ends of leaves in the carnivorous sundews (Drosera species) are alike. Indeed, Popping et al. have shown that touch-sensitive ‘snap-tentacles’ of D. glanduligera – near the edge of the tentacle tangle – catapult prey into the mass of sticky tentacles where they become adhered and trapped. Those latter tentacles more slowly convey the hapless victim – as if on a conveyor belt of death - towards its ultimate digestive fate. This combination of ‘snap-and-trap’ adds yet another dimension to the bizarre world of these fascinating zootrophs.
Image: Satu Suro/Wikimedia Commons.
Potential new herbicide
The contentious matter of plant GM (genetic manipulation – which always sounds more menacing and mankind-meddling-with-nature than GE, genetic engineering) has been put in the spotlight recently with Gilles-Eric Séralini et al.'s paper (Food and Chemical Toxicology 50: 4221–4231). Entitled ‘Long term toxicity of a Roundup herbicide and a Roundup-tolerant genetically modified maize’, it ascribes health and ‘longevity-shortening’ (i.e. earlier deaths …) effects in rats not only to the endocrine-disrupting effects of Roundup (commercial name for glyphosate, a herbicide; http://en.wikipedia.org/wiki/Roundup_%28herbicide%29), but also the over-expression of the transgene for glyphosate tolerance in GM maize and its metabolic consequences. Strong stuff indeed, and which has caused not a little concern and understandable ‘interest’ amongst the media (e.g. prompting a press release by the European Food Safety Authority; http://www.efsa.europa.eu/en/press/news/121004.htm). Leaving aside considerations about what this episode might tell us about the process of peer-review of scientific research, given the long-standing and enduring interest/concerns about Roundup and GM crops (e.g. http://monsantoblog.com/2012/09/24/), suggestion of an alternative to glyphosate will probably be welcomed. Encouraging news then that Sarah Barry et al. have elucidated a key step in production of thaxtomin (Nature Chemical Biology 8: 814–816, 2012). Thaxtomin, which exhibits herbicidal activity by inhibiting cellulose biosynthesis and thus interfering with formation of plant cell walls, is made naturally by Streptomyces species (http://en.wikipedia.org/wiki/Streptomyces), actinomycetous bacteria that cause the disease known as potato scab (http://en.wikipedia.org/wiki/Streptomyces_scabiei). Although thaxtomin's herbicidal nature has been known for some time, its commercialisation was not realistically possible without elucidation of its biosynthetic pathway. With Berry et al.'s identification of the particular P450 cytochrome enzyme (http://en.wikipedia.org/wiki/Cytochrome_P450) – TxtE – that catalyses an important step in thaxtomin synthesis, it is expected that the phytocide might now be made in amounts that could be commercially exploited (http://phys.org/news/2012-09-bacterial-disease-natural-herbicide.html#nwlt). And, as a ‘natural product’, it is apparently able to be used in agricultural systems that have the cachet (to say nothing of any ‘sales-price-premium’) accorded by their ‘organic’ status/certification (http://en.wikipedia.org/wiki/Organic_certification). (But probably best not to dwell on the fact that commercial amounts of this natural, organic herbicide may need to be produced by GM'd bacteria.)
Image: Ben Mills / Wikimedia Commons.
Potential new fertiliser
This month's winner in the ‘so simple it's positively brilliant (but why did nobody think of it before?)’ category is Damar López-Arredondo and Luis Herrera-Estrella's paper entitled, ‘Engineering phosphorous [sic.] metabolism in plants to produce a dual fertilization and weed control system’ (Nature Biotechnology 30: 889–893, 2012). Apart from the unusual spelling of phosphorus in the title (it is correct in the body of the article – and this is important since they are dealing with two similarly worded phosphorus compounds: phosphate and phosphite!), this is a most interesting piece of research. I can do no better than reproduce the paper's own rather elegant summary of the work (from Laboratorio Nacional de Genómica para la Biodiversidad, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Irapuato, Guanajuato, México) here: ‘High crop yields depend on the continuous input of orthophosphate (PO43–)-based fertilizers and herbicides. Two major challenges for agriculture are that phosphorus is a nonrenewable resource and that weeds have developed broad herbicide resistance. One strategy to overcome both problems is to engineer plants to outcompete weeds and microorganisms for limiting resources, thereby reducing the requirement for both fertilizers and herbicides. Plants and most microorganisms are unable to metabolize phosphite (PO33–), so we developed a dual fertilization and weed control system by generating transgenic plants [arabidopsis and tobacco] that can use phosphite as a sole phosphorus source. Under greenhouse conditions, these transgenic plants require 30–50 % less phosphorus input when fertilized with phosphite to achieve similar productivity to that obtained by the same plants using orthophosphate fertilizer and, when in competition with weeds, accumulate 2–10 times greater biomass than when fertilized with orthophosphate’. Or, and in summary, ‘the production of transgenic crop plants able to utilize phosphite, together with the application of phosphite as a source of phosphorus, might potentially become an effective phosphorus-fertilization and weed control scheme in the almost 67 % of cultivated land with low orthophosphate availability’. Whilst the authors are appropriately – and understandably – cautious about the significance of the results and how well they will scale-up to field-sized trials, this work – from the country whose CIMMYT (The International Maize and Wheat Improvement Center) was a major player in the Green Revolution (http://en.wikipedia.org/wiki/Green_Revolution) of the last century – sounds like another agronomic development with tremendous potential. ¡Muchas gracias!
Image: Tennessee Valley Authority, 1942/ Franklin D. Roosevelt Presidential Library and Museum.
Sports turf below PAR
Of all the incredible diversity of plants on this planet, arguably the grass family (the Poaceae; http://en.wikipedia.org/wiki/Poaceae) is one of the greatest of Nature's gifts to Mankind. Not only does it feed over half of the world's population as cereals, (http://en.wikipedia.org/wiki/Cereals), but as amenity grasslands and sports fields it allows us to relax with a wide range of ball games, contact sports and the like. So why don't we take just a little more care of it? Well, although those prized playing surfaces may be highly pampered in terms of watering, mowing, heating and nutrient regimes, we've overlooked the fact that they are photosynthetic organisms and if we cover them up their ability to photosynthesise and ‘look after themselves’ is impaired. So, timely that William Reynolds et al. have looked into this very problem (Crop Science 52: 2375–2384, 2012). But what they investigated isn't the long-term, big-scale covering-up of large manicured lawned areas with a tarpaulin or whatever, but the much smaller-scale, though longer-lasting week-in-week-out application and re-application of paint that marks out the various pitches and corporate sponsorship logos, etc. In summary, they found that paints reduce the amount of PAR (photosynthetically active radiation – wavelengths that are between 400 and 700 nm) penetrating to the grass below the markings. However, recognising the issue is one thing, what is done about it is more problematic. As the authors recognise, ‘… the delicate balance between producing bright, distinct logos and preserving turfgrass health is one that field managers need to dictate based on their individual situation’. One thing's for sure, this is one sports question that is now as likely to be discussed in the research seminar as it is down the pub!
Image: Wikimedia Commons.
Funds flood into plant water use research
For too long, CAM [crassulacean acid metabolism (http://en.wikipedia.org/wiki/Crassulacean_acid_metabolism), in which CO2 is fixed into an organic acid at night when stomata are open(!) in such plants and re-fixed via the Calvin–Benson–Bassham et al. Cycle – C3 photosynthesis (http://en.wikipedia.org/wiki/C3_photosynthesis) during daylight, when stomata are shut(!!)…] has been on the plant physiological sidelines as a quirky bit of biochemistry at one end of the spectrum of photosynthetic-variations-on-a-theme. But now it is poised to take centre stage as more water-efficient solutions for plant biology are sought as we enter a more water-frugal age. Famously, the water-use efficiency, which describes ‘a plant's photosynthetic production rate relative to the rate at which it transpires water to the atmosphere’ (e.g. Lucas Cernusak et al., New Phytologist 173: 294–305, 2007) of CAM plants is rather low, which is good. However, they do also tend to grow rather slowly – albeit in hotter climes than temperate ones – which is not so good if you are interested in high-yielding crops to feed a growing world population or generate lots of biomass in a hurry. But if you are concerned about the ability of today's plants to cope with drier, warmer climates in future, CAM might have a lot to offer. Well, if a new transatlantic alliance has its way CAM is set to invade the world of the C3 photosynthesisers with US$14·3 million of funding from the USA's Department of Energy (http://www.unr.edu/nevada-today/news/2012/cushman-cam-research). The dosh will be dished out amongst the Universities of Nevada and Tennessee (in the USA), Liverpool and Newcastle (in the UK), and the USA's Oak Ridge National Laboratory. Although crops may benefit from this research in the longer term, a more immediate shorter-term goal is to engineer CAM into the fast-growing biomass energy tree poplar so it can cope better with anticipated future growing conditions. CAM, coupled with a genetically engineered semi-dwarf stature in poplar (Ani Elias et al., Plant Physiology 160: 1130–1144, 2012), may be a ‘negative double-whammy’ (http://en.wikipedia.org/wiki/Double_Whammy) that can deliver tree phenotypes that are not only more water-use-efficient, but advantageous for short-rotation forestry (http://en.wikipedia.org/wiki/Short_rotation_forestry) and biomass energy (http://en.wikipedia.org/wiki/Biomass_energy_crop) purposes. So, no longer will CAM be the exclusive preserve of such exotics as pineapples, epiphytic orchids and Crassula species, and the notion of poplar as a ‘facultative CAM plant’ – a sort of Mesembryanthemum crystallinum of the temperate forest (Charlotte Lin, Journal of Undergraduate Life Sciences 3: 64–66, 2009) – might just be science fiction turned into science fact. However, if Ming Yuan et al.'s work (Tree Physiology 32: 188–199, 2012) on Camellia – ‘tree-like shrubs’ – is widely applicable, then CAM can be induced in C3 species (such as, say – and chosen entirely at random you understand – poplar) by the much cheaper option of fungus infection. Hmmm, who'll be the first to tell the UK–USA team/DoE that..?
Image: Wikimedia Coomons.