- Email: [email protected]
More GM tomatoes
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trends in plant science Headlines New ways for old genes We already know from classical physiological studies that plant signals interact with each other to generate downstream developmental responses. Arabidopsis genetics is now about to identify the molecular links between signaling pathways in plants. Recently, five groups have identified mutations in genes that had been previously implicated in other pathways, revealing interactions between abscisic acid (ABA) and ethylene signal transduction as well as between ABA and sugar signaling. Recently, Majid Ghassemian et al.1 and Nathalie Beaudoin et al.2 reported that they recovered alleles of ein2 in genetic screens for mutants with enhanced responses to ABA at seed germination. The EIN2 locus had previously been shown to determine sensitivity to another plant hormone, ethylene. In parallel, Francisco Arenas-Huertero et al.3, Ron Laby et al.4 and Casper Huijser et al.5 reported that they isolated alleles of abi4 in mutant screens for sugar insensitivity during seedling development. A mutation in ABI4 was originally shown to confer resistance to ABA at seed germination. Altogether, these findings show that ABA and ethylene, along with sugar and ABA transduction pathways, share common genetic determinants. However, the connections between these two pairs of signaling cascades are not restricted to one genetically defined step in the cascade. Mutations in other
Green tea lowers cholesterol Christina Bursill and Paul Roach (CSIRO, Adelaide, SA, Australia) have shown that antioxidants in green tea, called catechins, can
elements of the ethylene transduction pathway, such as ctr1, which confers constitutive response to ethylene, or etr1, which is a member of the ethylene receptor family, also modulate seed sensitivity to ABA during germination. In fact, Beaudoin et al. also recovered ctr1 in a screen for decreased sensitivity to ABA. This suggests that the ethylene transduction pathway impinges on the ABA signaling cascade to regulate seed germination. In the case of the interplay between sugar sensing and ABA signaling, ABI4 plays a prominent role whereas mutations in other ABI genes have little or no influence on the sugar sensitivity of seedling development. However, mutants impaired in ABA biosynthesis are also insensitive to sugar, suggesting that ABA production is required for sugar sensing. These interesting findings point to an extensive cross talk between ABA and another stress signal molecule, ethylene, and between ABA and the sugar nutrient-sensing pathways. However, these are probably just flashes of light on parts of the transduction networks that allow plants to integrate diverse signals such as environmental signals, nutrient status and developmental signals to produce adaptive responses. Further studies show that ethylene and ABA signaling pathways also interact to regulate root development but, in this organ, mutations that confer ethylene insensitivity also decrease ABA-mediated inhibition of
root growth1,2. Hopefully, new tools such as DNA microarrays, which enable us to monitor changes in gene expression triggered by a signal or a mutation on a genome wide scale, should help us to uncover the molecular basis for signal cross talk in plants in more detail.
lower cholesterol in rabbits by increasing the quantity of a liver’s LDL receptors, which work to clear cholesterol from the blood. Black tea contains much lower levels of catechins because they are oxidized during processing. Studies by other researchers suggest
that humans could lower their cholesterol levels by up to 10% if they habitually consumed between five to ten cups of green tea daily (for more information e-mail paul.roach@ hsn.csiro.au).
More GM tomatoes Autar Mattoo and colleagues (Agricultural Research Service, Beltsville, MA, USA) have developed a novel way of slowing down tomato ripening by introducing a yeast gene that controls this function in the fruit (Fig. 1). The new transgenic tomatoes also have a lycopene content, a carotenoid with positive qualities for eyesight, cancer prevention and cardiovascular health, which is 2.5 times higher than non-transgenic tomatoes (www.ars.usda.gov/is/AR/archive/sep00/ tomato0900.htm). Fig. 1. Autar Mattoo examines tomato plants genetically engineered to enhance phytonutrient content and longevity of the fruit. Photograph by Scott Bauer, courtesy of USDA, USA.
1360 - 1385/00/$ – see front matter © 2000 Elsevier Science Ltd. All rights reserved.
Sébastien Thomine (e-mail [email protected]) References 1 Ghassemian, M. et al. (2000) Regulation of abscisic acid signaling by the ethylene response pathway in Arabidopsis. Plant Cell 12, 1117–1126 2 Beaudoin, N. et al. (2000) Interactions between abscisic acid and ethylene signaling cascades. Plant Cell 12, 1103–1115 3 Arenas-Huertero, F. et al. (2000) Analysis of Arabidopsis glucose insensitive mutants, gin5 and gin6, reveals a central role of the plant hormone ABA in the regulation of plant vegetative development by sugar. Genes Dev. 14, 2085–2096 4 Laby, R.J. et al. (2000) The Arabidopsis sugarinsensitive mutants sis4 and sis5 are defective in abscisic acid synthesis and response. Plant J. 23, 587–596 5 Huijser, C. et al. (2000) The Arabidopsis SUCROSE UNCOUPLED-6 gene is identical to ABSCISIC ACID INSENSITIVE-4: involvement of abscisic acid in sugar responses. Plant J. 23, 577–585
GM crops welcome in China GM Bt rice varieties of Minghui 63 and Shanyou 63, two high-yield ‘hybrids’, have passed an important field test in Wuhan, China, and stood up to two common pests, leaffolder and yellow stem borer. Rice yields were 28.9% higher than non-Bt plants, an impressive result gained without the use of chemicals. The Institute of Microbe Research, under the Chinese Academy of Sciences (CAS), introduced an anti-virus, genetically modified tobacco seed and carried out the first field experiments in 1992. The Institute of Genetics under CAS developed eight types of anti-pest hybrid rice at about the same time. Although six GM varieties, including tomatoes and cotton, have been given licenses for commercial promotion by the Ministry of Agriculture in China, only two types of cotton seeds are December 2000, Vol. 5, No. 12
515
17/11/00
10:24
Page 515
trends in plant science Headlines New ways for old genes We already know from classical physiological studies that plant signals interact with each other to generate downstream developmental responses. Arabidopsis genetics is now about to identify the molecular links between signaling pathways in plants. Recently, five groups have identified mutations in genes that had been previously implicated in other pathways, revealing interactions between abscisic acid (ABA) and ethylene signal transduction as well as between ABA and sugar signaling. Recently, Majid Ghassemian et al.1 and Nathalie Beaudoin et al.2 reported that they recovered alleles of ein2 in genetic screens for mutants with enhanced responses to ABA at seed germination. The EIN2 locus had previously been shown to determine sensitivity to another plant hormone, ethylene. In parallel, Francisco Arenas-Huertero et al.3, Ron Laby et al.4 and Casper Huijser et al.5 reported that they isolated alleles of abi4 in mutant screens for sugar insensitivity during seedling development. A mutation in ABI4 was originally shown to confer resistance to ABA at seed germination. Altogether, these findings show that ABA and ethylene, along with sugar and ABA transduction pathways, share common genetic determinants. However, the connections between these two pairs of signaling cascades are not restricted to one genetically defined step in the cascade. Mutations in other
Green tea lowers cholesterol Christina Bursill and Paul Roach (CSIRO, Adelaide, SA, Australia) have shown that antioxidants in green tea, called catechins, can
elements of the ethylene transduction pathway, such as ctr1, which confers constitutive response to ethylene, or etr1, which is a member of the ethylene receptor family, also modulate seed sensitivity to ABA during germination. In fact, Beaudoin et al. also recovered ctr1 in a screen for decreased sensitivity to ABA. This suggests that the ethylene transduction pathway impinges on the ABA signaling cascade to regulate seed germination. In the case of the interplay between sugar sensing and ABA signaling, ABI4 plays a prominent role whereas mutations in other ABI genes have little or no influence on the sugar sensitivity of seedling development. However, mutants impaired in ABA biosynthesis are also insensitive to sugar, suggesting that ABA production is required for sugar sensing. These interesting findings point to an extensive cross talk between ABA and another stress signal molecule, ethylene, and between ABA and the sugar nutrient-sensing pathways. However, these are probably just flashes of light on parts of the transduction networks that allow plants to integrate diverse signals such as environmental signals, nutrient status and developmental signals to produce adaptive responses. Further studies show that ethylene and ABA signaling pathways also interact to regulate root development but, in this organ, mutations that confer ethylene insensitivity also decrease ABA-mediated inhibition of
root growth1,2. Hopefully, new tools such as DNA microarrays, which enable us to monitor changes in gene expression triggered by a signal or a mutation on a genome wide scale, should help us to uncover the molecular basis for signal cross talk in plants in more detail.
lower cholesterol in rabbits by increasing the quantity of a liver’s LDL receptors, which work to clear cholesterol from the blood. Black tea contains much lower levels of catechins because they are oxidized during processing. Studies by other researchers suggest
that humans could lower their cholesterol levels by up to 10% if they habitually consumed between five to ten cups of green tea daily (for more information e-mail paul.roach@ hsn.csiro.au).
More GM tomatoes Autar Mattoo and colleagues (Agricultural Research Service, Beltsville, MA, USA) have developed a novel way of slowing down tomato ripening by introducing a yeast gene that controls this function in the fruit (Fig. 1). The new transgenic tomatoes also have a lycopene content, a carotenoid with positive qualities for eyesight, cancer prevention and cardiovascular health, which is 2.5 times higher than non-transgenic tomatoes (www.ars.usda.gov/is/AR/archive/sep00/ tomato0900.htm). Fig. 1. Autar Mattoo examines tomato plants genetically engineered to enhance phytonutrient content and longevity of the fruit. Photograph by Scott Bauer, courtesy of USDA, USA.
1360 - 1385/00/$ – see front matter © 2000 Elsevier Science Ltd. All rights reserved.
Sébastien Thomine (e-mail [email protected]) References 1 Ghassemian, M. et al. (2000) Regulation of abscisic acid signaling by the ethylene response pathway in Arabidopsis. Plant Cell 12, 1117–1126 2 Beaudoin, N. et al. (2000) Interactions between abscisic acid and ethylene signaling cascades. Plant Cell 12, 1103–1115 3 Arenas-Huertero, F. et al. (2000) Analysis of Arabidopsis glucose insensitive mutants, gin5 and gin6, reveals a central role of the plant hormone ABA in the regulation of plant vegetative development by sugar. Genes Dev. 14, 2085–2096 4 Laby, R.J. et al. (2000) The Arabidopsis sugarinsensitive mutants sis4 and sis5 are defective in abscisic acid synthesis and response. Plant J. 23, 587–596 5 Huijser, C. et al. (2000) The Arabidopsis SUCROSE UNCOUPLED-6 gene is identical to ABSCISIC ACID INSENSITIVE-4: involvement of abscisic acid in sugar responses. Plant J. 23, 577–585
GM crops welcome in China GM Bt rice varieties of Minghui 63 and Shanyou 63, two high-yield ‘hybrids’, have passed an important field test in Wuhan, China, and stood up to two common pests, leaffolder and yellow stem borer. Rice yields were 28.9% higher than non-Bt plants, an impressive result gained without the use of chemicals. The Institute of Microbe Research, under the Chinese Academy of Sciences (CAS), introduced an anti-virus, genetically modified tobacco seed and carried out the first field experiments in 1992. The Institute of Genetics under CAS developed eight types of anti-pest hybrid rice at about the same time. Although six GM varieties, including tomatoes and cotton, have been given licenses for commercial promotion by the Ministry of Agriculture in China, only two types of cotton seeds are December 2000, Vol. 5, No. 12
515