- Email: [email protected]
Plankton protects grain stores
News & Comment
suggesting that SDE3 is required for the maintenance but not the initiation of TRV silencing. In contrast with cucumber mosaic virus (CMV), there was an increase in viral RNA and an overall reduction in PTGS in sde3 plants, suggesting an effect on initiation. Dalmay et al. suggest that the sde3 mutation affects the silencing by the two viruses in different ways because they have different strategies for defense against PTGS. TRV might not produce an RNA species acted on by SDE3 during the initiation of gene silencing, whereas CMV does.
‘…sde3 is necessary for the initiation of transgene-mediated silencing, but only for maintenance of silencing by tobacco rattle virus…’ Cloning of the sde3 locus revealed a protein with homology to RNA helicases.
TRENDS in Plant Science Vol.6 No.8 August 2001
345
According to the current model of RNAbased silencing, an RNA helicase probably contributes to the production of dsRNA by creating additional single stranded RNA templates for an RNA-dependent RNA polymerase (RdRP). Although the RNA helicase domain of SDE3 is highly homologous to previously identified RNA helicases involved in RNA silencing in other species, it lacks other important motifs. This suggests that it might not be the functional homologue of these genes. The milder defect in PTGS in sde3 than in sde1 (an RdRP) mutants, and the fact that C. elegans displays efficient dsRNA silencing and yet lacks an RNA helicase of the sde3 subfamily, suggest that sde3 might be a regulator of PTGS rather than an essential factor. The phenotype of the sde3 mutants suggests some alternative explanations beyond those provided by Dalmay et al.
The effect of sde3 on transgene-mediated silencing and viral-mediated silencing might not be different. In both cases, silencing is initiated and maintained at an original site, but is not found in newer tissues. These observations suggest that the sde3 deficiency might be preventing the systemic spread of silencing. Alternatively, sde3 might be more generally involved in maintenance in both instances. Also, as transgene silencing is only seen in tissues of embryonic origin, a maternal effect might be at play.
use the technology to avoid over application of fertilizers. [Reay, D. (2001) New Sci. 3 June, p. 54] TS
fetuses,’ Tobin told a recent meeting of horse breeders. [McCarthy, D. (2001) The Press (Christchurch, New Zealand), Racing section, p. 30] TS
1 Dalmay, T. et al. (2001) SDE3 encodes an RNA helicase required for post-transcriptional gene silencing in Arabidopsis. EMBO J. 20, 2069–2077
Matthew R. Willmann [email protected]
In Brief
‘T’ is for teeth Thanks to research from a College of Dentistry team at the University of Illinois (USA), drinkers of tea (‘the cup that cheers’) might have even more reason to smile. The group has found that compounds in tea destroy cavity-causing bacteria, and if included as part of a normal oral-hygiene routine, tea drinking might lead to a reduction in dental cavities. Although their work related specifically to black tea (which constitutes ~80% of the world tea consumption), it adds to similar results that had been found previously for green tea, which is favored in Japan. Additionally, tea is one of the few dietary sources of fluoride that helps to strengthen teeth. [Chapman, J. (2001) Daily Mail, 23 May, p. 35] NC
Colorful idea Leaf color might enable scientists to determine how well plants are fed says David Reay (University of Edinburgh, UK). When each of the three main nutrients (nitrogen, phosphorus and potassium) required for plant growth is in short supply, leaves change color in a specific manner. Deficiencies in nitrogen, phosphorus and potassium lead to yellowing, purpling or leaf-edge browning, respectively. A sensor could determine the color of the leaves, which would give scientists an idea of the nutrient supply of the plant. Farmers could http://plants.trends.com
Cherry trees harm horse business
Photograph courtesy of Scott Bauer, USDA.
Cherry trees might be the cause of the worst devastation in the history of horse breeding in the state of Kentucky (USA), which is famous for its equine breeding. With >1200 natural abortions to date, the multi-billion $US crisis has led scientists to search exhaustively for the cause. Tom Tobin, a toxicologist at the Gluck Equine Research Centre, concluded that cyanide has infiltrated Kentucky pastures from the many surrounding black cherry trees (Prunus serotina). An unexpected ‘hot to frozen’ weather pattern in April caused the cherrytree leaves to wilt earlier than usual, which released cyanide into the pastures. ‘There is preliminary evidence of cyanide in aborted
Vegetables need space to grow Recent experiments conducted by Chinese scientists suggest that exposure of seeds to the conditions found in space significantly promote the growth of the resulting plants. Reports suggest that rice (Oryza sativa) and peppers (Capsicum spp.) grown from such seed have higher levels of vitamin C, and that some types of melon grow larger and sweeter than their terrestrial counterparts. These effects have been attributed to high levels of radiation and low gravity experienced by the seeds during their space flight. However, NASA – the US space agency – has not reported such effects in its own experiments. [Daily Mail (2001), 28 May, p. 19] NC
Plankton protects grain stores Scientists at the University of Greenwich (London, UK) want to raise awareness of a grain storage method that Chinese farmers used 4000 years ago. Farmers stored grain along with diatomaceous earth (DE), a chalky rock that came from the fossilized remains of plankton. DE, an alternative to the pesticides currently in use, kills insects
1360-1385/01/$ – see front matter © 2001 Elsevier Science Ltd. All rights reserved.
346
News & Comment
by attacking the waxy covering on the outside of their bodies. Tanya Stathers, a researcher at the Natural Resources Institute in Greenwich told reporters, ‘DE could offer a locally available, cheaper, healthier and more environmentally friendly alternative. It is already being used in large-scale grain treatment in Australia.’ [von Radowitz, J. (2001) The Press Association, 29 May] TS
Robots push plants to grow Thigmomorphogenesis is a technique whereby brushing the tips of growing plants results in sturdier vegetation. With the technique in mind, researchers in the UK created Dr Green, a robot that strokes seedlings. David Carey of Hadlow College said, ‘Stroking seedlings once a day makes them 30% stockier.’ Tony Dodson, at Greenwich University, designed Dr Green, which is now being tested on a large scale by a UK bedding-plant producer. Some plants that get the robot’s touch have greater insect resistance suggesting that the robot could cut down on chemical controls of pests. How brushing plants increases their vigor is unclear. [Uhlig, R. (2001) The Daily Telegraph (London), 12 June, p. 13] TS
Restricting water supply enhances crop growth
Satellite water snoops
Treating wood, a hot topic
Satellites are being used to measure water loss from plants on Earth. Hamlyn Jones (Dundee University, UK) is the leader of the international team that will use satellitegenerated images of leaf temperatures to create maps of vegetative evaporation across Europe. The method should enable researchers to measure how different ecosystems use water, and should assist water policy makers in important decisions. Water use worldwide has tripled in the past 50 years. ‘The need for accurate methods of measuring water systems has never been greater’ says Jones. [Montgomery, D. (2001) The Scotsman, 6 June, p. 4] TS
In spite of its inert appearance, the sugars within wood are an ideal food source for rot fungi that severely limit the longevity of timber products. However, in a new process that involves heating the wood to 200°C, many changes take place that not only improve the resistance of the timber to fungal attack, but also result in reduced shrinkage and swelling, thereby improving its usefulness. Additionally, the heat treatment, developed by the Finnish organization Stellac Oy, imparts a pleasing brown color to the wood, which makes it an attractive alternative to the use of expensive tropical timbers. [http://www.stellac.fi/ english/index.htm] NC
Blue means bad Transgenic plants can now detect toxic metals in contaminated soils [Nat. Biotechnol. (2001) 19, 568–572; Trends Plant Sci. (2001) 6, 306–310]. Olga Kovalchuk and colleagues designed genetically engineered plants that contain a GUS reporter gene, which generates blue spots when the marker gene undergoes base pair mutation or homologous recombination. The study shows that in a laboratory setting, transgenic Arabidopsis plants detect increased levels of mutation and recombination in the presence of heavy metals. Mutation rates depend on the concentration and uptake of the heavy metals. The researchers also planted the metal-sniffing plants on contaminated soil near an oil refinery and showed a significant increase in mutation and recombination. TS
Junked java
Water is essential for plant growth; yet, it seems that allowing some roots to dry out does not impair crop yields. This counterintuitive discovery has led to the development of partial root drying (PRD) by scientists at Lancaster University (UK). The PRD technique relies on the fact that the abscisic acid produced by roots when encountering dry soil promotes stomatal closure and suppresses leaf formation. Not only does this prevent significant waterstress from developing, but fruit growth is also maintained and fruit flavor can even be improved. Compared with other deficit-based irrigation systems, PRDtreated crops did not suffer damaging water deficits, and trials are now being undertaken worldwide. NC http://plants.trends.com
TRENDS in Plant Science Vol.6 No.8 August 2001
Scientists are thinking up new uses for the coffee bean because of a worldwide surplus of the commodity. In the present market, although production and surplus are high, the crop’s value is low. To reverse the price slump, Central and South American countries have adopted measures that will use 5% of their lowest grade coffee for purposes other than the coffee cup. Currently, scientists are developing java as a source of construction materials and fuel. Guatemalan tests began in April when a cement factory used blackened and fermented beans to fire the ovens. Dias Cardenas, researcher at Chapingo University (Veracruz, Mexico), told reporters that local farmers are already selling their rejected beans to industry. [Jordan, P. (2001) Reuters, 5 June] TS
Wine as smooth as silk?
Photograph courtesy of Scott Bauer, USDA.
The world of wine seems set to be the next beneficiary of the attention of plant genetic engineers. Pierce’s disease is a bacterial infection of grapevines that affects the xylem and ultimately kills the plant. To date, the infected vines cannot be treated and there are no resistant varieties. US scientists have solved this problem by engineering the silkworm cecropin gene into grape plants. Cecropin sticks to and punctures the bacterial membrane, killing the bacteria. However, whether the wine industry – or its customers – will find this solution easy to swallow remains to be seen. [Samuel, E. (2001) New Sci., 26 May, p. 6] NC
Tasty mutant It seems that some Arabidopsis plants are more appetizing to eat than others. Georg Jander and colleagues [Plant Physiol. (2001) 126, 890–898] found that the insect herbivore Trichoplusia ni, or cabbage looper, ravages the Landsberg type of
1360-1385/01/$ – see front matter © 2001 Elsevier Science Ltd. All rights reserved.
suggesting that SDE3 is required for the maintenance but not the initiation of TRV silencing. In contrast with cucumber mosaic virus (CMV), there was an increase in viral RNA and an overall reduction in PTGS in sde3 plants, suggesting an effect on initiation. Dalmay et al. suggest that the sde3 mutation affects the silencing by the two viruses in different ways because they have different strategies for defense against PTGS. TRV might not produce an RNA species acted on by SDE3 during the initiation of gene silencing, whereas CMV does.
‘…sde3 is necessary for the initiation of transgene-mediated silencing, but only for maintenance of silencing by tobacco rattle virus…’ Cloning of the sde3 locus revealed a protein with homology to RNA helicases.
TRENDS in Plant Science Vol.6 No.8 August 2001
345
According to the current model of RNAbased silencing, an RNA helicase probably contributes to the production of dsRNA by creating additional single stranded RNA templates for an RNA-dependent RNA polymerase (RdRP). Although the RNA helicase domain of SDE3 is highly homologous to previously identified RNA helicases involved in RNA silencing in other species, it lacks other important motifs. This suggests that it might not be the functional homologue of these genes. The milder defect in PTGS in sde3 than in sde1 (an RdRP) mutants, and the fact that C. elegans displays efficient dsRNA silencing and yet lacks an RNA helicase of the sde3 subfamily, suggest that sde3 might be a regulator of PTGS rather than an essential factor. The phenotype of the sde3 mutants suggests some alternative explanations beyond those provided by Dalmay et al.
The effect of sde3 on transgene-mediated silencing and viral-mediated silencing might not be different. In both cases, silencing is initiated and maintained at an original site, but is not found in newer tissues. These observations suggest that the sde3 deficiency might be preventing the systemic spread of silencing. Alternatively, sde3 might be more generally involved in maintenance in both instances. Also, as transgene silencing is only seen in tissues of embryonic origin, a maternal effect might be at play.
use the technology to avoid over application of fertilizers. [Reay, D. (2001) New Sci. 3 June, p. 54] TS
fetuses,’ Tobin told a recent meeting of horse breeders. [McCarthy, D. (2001) The Press (Christchurch, New Zealand), Racing section, p. 30] TS
1 Dalmay, T. et al. (2001) SDE3 encodes an RNA helicase required for post-transcriptional gene silencing in Arabidopsis. EMBO J. 20, 2069–2077
Matthew R. Willmann [email protected]
In Brief
‘T’ is for teeth Thanks to research from a College of Dentistry team at the University of Illinois (USA), drinkers of tea (‘the cup that cheers’) might have even more reason to smile. The group has found that compounds in tea destroy cavity-causing bacteria, and if included as part of a normal oral-hygiene routine, tea drinking might lead to a reduction in dental cavities. Although their work related specifically to black tea (which constitutes ~80% of the world tea consumption), it adds to similar results that had been found previously for green tea, which is favored in Japan. Additionally, tea is one of the few dietary sources of fluoride that helps to strengthen teeth. [Chapman, J. (2001) Daily Mail, 23 May, p. 35] NC
Colorful idea Leaf color might enable scientists to determine how well plants are fed says David Reay (University of Edinburgh, UK). When each of the three main nutrients (nitrogen, phosphorus and potassium) required for plant growth is in short supply, leaves change color in a specific manner. Deficiencies in nitrogen, phosphorus and potassium lead to yellowing, purpling or leaf-edge browning, respectively. A sensor could determine the color of the leaves, which would give scientists an idea of the nutrient supply of the plant. Farmers could http://plants.trends.com
Cherry trees harm horse business
Photograph courtesy of Scott Bauer, USDA.
Cherry trees might be the cause of the worst devastation in the history of horse breeding in the state of Kentucky (USA), which is famous for its equine breeding. With >1200 natural abortions to date, the multi-billion $US crisis has led scientists to search exhaustively for the cause. Tom Tobin, a toxicologist at the Gluck Equine Research Centre, concluded that cyanide has infiltrated Kentucky pastures from the many surrounding black cherry trees (Prunus serotina). An unexpected ‘hot to frozen’ weather pattern in April caused the cherrytree leaves to wilt earlier than usual, which released cyanide into the pastures. ‘There is preliminary evidence of cyanide in aborted
Vegetables need space to grow Recent experiments conducted by Chinese scientists suggest that exposure of seeds to the conditions found in space significantly promote the growth of the resulting plants. Reports suggest that rice (Oryza sativa) and peppers (Capsicum spp.) grown from such seed have higher levels of vitamin C, and that some types of melon grow larger and sweeter than their terrestrial counterparts. These effects have been attributed to high levels of radiation and low gravity experienced by the seeds during their space flight. However, NASA – the US space agency – has not reported such effects in its own experiments. [Daily Mail (2001), 28 May, p. 19] NC
Plankton protects grain stores Scientists at the University of Greenwich (London, UK) want to raise awareness of a grain storage method that Chinese farmers used 4000 years ago. Farmers stored grain along with diatomaceous earth (DE), a chalky rock that came from the fossilized remains of plankton. DE, an alternative to the pesticides currently in use, kills insects
1360-1385/01/$ – see front matter © 2001 Elsevier Science Ltd. All rights reserved.
346
News & Comment
by attacking the waxy covering on the outside of their bodies. Tanya Stathers, a researcher at the Natural Resources Institute in Greenwich told reporters, ‘DE could offer a locally available, cheaper, healthier and more environmentally friendly alternative. It is already being used in large-scale grain treatment in Australia.’ [von Radowitz, J. (2001) The Press Association, 29 May] TS
Robots push plants to grow Thigmomorphogenesis is a technique whereby brushing the tips of growing plants results in sturdier vegetation. With the technique in mind, researchers in the UK created Dr Green, a robot that strokes seedlings. David Carey of Hadlow College said, ‘Stroking seedlings once a day makes them 30% stockier.’ Tony Dodson, at Greenwich University, designed Dr Green, which is now being tested on a large scale by a UK bedding-plant producer. Some plants that get the robot’s touch have greater insect resistance suggesting that the robot could cut down on chemical controls of pests. How brushing plants increases their vigor is unclear. [Uhlig, R. (2001) The Daily Telegraph (London), 12 June, p. 13] TS
Restricting water supply enhances crop growth
Satellite water snoops
Treating wood, a hot topic
Satellites are being used to measure water loss from plants on Earth. Hamlyn Jones (Dundee University, UK) is the leader of the international team that will use satellitegenerated images of leaf temperatures to create maps of vegetative evaporation across Europe. The method should enable researchers to measure how different ecosystems use water, and should assist water policy makers in important decisions. Water use worldwide has tripled in the past 50 years. ‘The need for accurate methods of measuring water systems has never been greater’ says Jones. [Montgomery, D. (2001) The Scotsman, 6 June, p. 4] TS
In spite of its inert appearance, the sugars within wood are an ideal food source for rot fungi that severely limit the longevity of timber products. However, in a new process that involves heating the wood to 200°C, many changes take place that not only improve the resistance of the timber to fungal attack, but also result in reduced shrinkage and swelling, thereby improving its usefulness. Additionally, the heat treatment, developed by the Finnish organization Stellac Oy, imparts a pleasing brown color to the wood, which makes it an attractive alternative to the use of expensive tropical timbers. [http://www.stellac.fi/ english/index.htm] NC
Blue means bad Transgenic plants can now detect toxic metals in contaminated soils [Nat. Biotechnol. (2001) 19, 568–572; Trends Plant Sci. (2001) 6, 306–310]. Olga Kovalchuk and colleagues designed genetically engineered plants that contain a GUS reporter gene, which generates blue spots when the marker gene undergoes base pair mutation or homologous recombination. The study shows that in a laboratory setting, transgenic Arabidopsis plants detect increased levels of mutation and recombination in the presence of heavy metals. Mutation rates depend on the concentration and uptake of the heavy metals. The researchers also planted the metal-sniffing plants on contaminated soil near an oil refinery and showed a significant increase in mutation and recombination. TS
Junked java
Water is essential for plant growth; yet, it seems that allowing some roots to dry out does not impair crop yields. This counterintuitive discovery has led to the development of partial root drying (PRD) by scientists at Lancaster University (UK). The PRD technique relies on the fact that the abscisic acid produced by roots when encountering dry soil promotes stomatal closure and suppresses leaf formation. Not only does this prevent significant waterstress from developing, but fruit growth is also maintained and fruit flavor can even be improved. Compared with other deficit-based irrigation systems, PRDtreated crops did not suffer damaging water deficits, and trials are now being undertaken worldwide. NC http://plants.trends.com
TRENDS in Plant Science Vol.6 No.8 August 2001
Scientists are thinking up new uses for the coffee bean because of a worldwide surplus of the commodity. In the present market, although production and surplus are high, the crop’s value is low. To reverse the price slump, Central and South American countries have adopted measures that will use 5% of their lowest grade coffee for purposes other than the coffee cup. Currently, scientists are developing java as a source of construction materials and fuel. Guatemalan tests began in April when a cement factory used blackened and fermented beans to fire the ovens. Dias Cardenas, researcher at Chapingo University (Veracruz, Mexico), told reporters that local farmers are already selling their rejected beans to industry. [Jordan, P. (2001) Reuters, 5 June] TS
Wine as smooth as silk?
Photograph courtesy of Scott Bauer, USDA.
The world of wine seems set to be the next beneficiary of the attention of plant genetic engineers. Pierce’s disease is a bacterial infection of grapevines that affects the xylem and ultimately kills the plant. To date, the infected vines cannot be treated and there are no resistant varieties. US scientists have solved this problem by engineering the silkworm cecropin gene into grape plants. Cecropin sticks to and punctures the bacterial membrane, killing the bacteria. However, whether the wine industry – or its customers – will find this solution easy to swallow remains to be seen. [Samuel, E. (2001) New Sci., 26 May, p. 6] NC
Tasty mutant It seems that some Arabidopsis plants are more appetizing to eat than others. Georg Jander and colleagues [Plant Physiol. (2001) 126, 890–898] found that the insect herbivore Trichoplusia ni, or cabbage looper, ravages the Landsberg type of
1360-1385/01/$ – see front matter © 2001 Elsevier Science Ltd. All rights reserved.