World wheat grain yields increased substantially in the 1960s and 1970s because farmers rapidly adopted the new varieties and cultivation methods of the so-called 'green revolution'. The new varieties are shorter, increase grain yield at the expense of straw biomass, and are more resistant to damage by wind and rain. These wheats are short because they respond abnormally to the plant growth hormone gibberellin. This reduced response to gibberellin is conferred by mutant dwarfing alleles at one of two Reduced height-1 (Rht-B1 and Rht-D1) loci. Here we show that Rht-B1/Rht-D1 and maize dwarf-8 (d8) are orthologues of the Arabidopsis Gibberellin Insensitive (GAI) gene. These genes encode proteins that resemble nuclear transcription factors and contain an SH2-like domain, indicating that phosphotyrosine may participate in gibberellin signalling. Six different orthologous dwarfing mutant alleles encode proteins that are altered in a conserved amino-terminal gibberellin signalling domain. Transgenic rice plants containing a mutant GAI allele give reduced responses to gibberellin and are dwarfed, indicating that mutant GAI orthologues could be used to increase yield in a wide range of crop species.

Imagine a world in which any protein, either naturally occurring or designed by man, could be produced safely, inexpensively and in almost unlimited quantities using only simple nutrients, water and sunlight. This could one day become reality as we learn to harness the power of plants for the production of recombinant proteins on an agricultural scale. Molecular farming in plants has already proven to be a successful way of producing a range of technical proteins. The first plant-derived recombinant pharmaceutical proteins are now approaching commercial approval, and many more are expected to follow.

SummaryBacillus thuringiensis (Bt) is a soil bacterium that forms spores during the stationary phase of its growth cycle. The spores contain crystals, predominantly comprising one or more Cry and ⁄ or Cyt proteins (also known as d-endotoxins) that have potent and specific insecticidal activity. Different strains of Bt produce different types of toxin, each of which affects a narrow taxonomic group of insects. Therefore, Bt toxins have been used as topical pesticides to protect crops, and more recently the proteins have been expressed in transgenic plants to confer inherent pest resistance. Bt transgenic crops have been overwhelmingly successful and beneficial, leading to higher yields and reducing the use of chemical pesticides and fossil fuels. However, their deployment has attracted some criticism particularly with regard to the potential evolution of pest-resistant insect strains. Here, we review recent progress in the development of Bt technology and the countermeasures that have been introduced to prevent the evolution of resistant insect populations.

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We have generated transgenic rice plants expressing the Datura stramonium adc gene and investigated their response to drought stress. We monitored the steady-state mRNA levels of genes involved in polyamine biosynthesis (Datura adc, rice adc, and rice samdc) and polyamine levels. Wild-type plants responded to the onset of drought stress by increasing endogenous putrescine levels, but this was insufficient to trigger the conversion of putrescine into spermidine and spermine (the agents that are believed to protect plants under stress). In contrast, transgenic plants expressing Datura adc produced much higher levels of putrescine under stress, promoting spermidine and spermine synthesis and ultimately protecting the plants from drought. We demonstrate clearly that the manipulation of polyamine biosynthesis in plants can produce drought-tolerant germplasm, and we propose a model consistent with the role of polyamines in the protection of plants against abiotic stress.A biotic stresses such as drought represent some of the most significant constraints to agricultural productivity. Transgenic approaches can be used in combination with conventional breeding strategies to create crops with enhanced drought tolerance, and one way in which this can be achieved is through the manipulation of polyamine metabolism. Polyamines are small, ubiquitous, nitrogenous compounds that have been implicated in a variety of stress responses in plants (1). The link between polyamines and abiotic stress was first documented through putrescine accumulation in response to suboptimal potassium levels in barley (2). Since then, a connection has been suggested between increased putrescine levels and abiotic stress (3). Similar phenomena have been described in animals, e.g., during ischemic and postischemic responses in neurons (4). The physiological role of putrescine in abiotic stress responses is a matter of controversy. It has been very difficult to establish a direct cause-and-effect relationship between increased putrescine levels in plants and abiotic stress. Elevated putrescine might be the cause of stress-induced injury or, alternatively, a protective response resulting from stress (5).The genetic manipulation of polyamine metabolism has become a valuable tool for studying their physiological roles in plants (6). Plant polyamine content has been modulated by the overexpression͞down-regulation of arginine decarboxylase (adc), ornithine decarboxylase (odc), and S-adenosylmethionine decarboxylase (samdc) (6-10). Overexpression of heterologous adc or odc cDNAs in plants generally results in the production of high levels of putrescine (11-13). In most cases, this is accompanied by a relatively small increase in spermidine and spermine concentrations (7,14). Such findings suggest that the levels of spermidine and spermine are under strict homeostatic regulation (15). Therefore, the study of plants transformed with genes involved in polyamine biosynthesis may shed light on the importance of polyamines, their role in the acquisition of stress ...

Vitamin deficiency affects up to 50% of the world's population, disproportionately impacting on developing countries where populations endure monotonous, cereal-rich diets. Transgenic plants offer an effective way to increase the vitamin content of staple crops, but thus far it has only been possible to enhance individual vitamins. We created elite inbred South African transgenic corn plants in which the levels of 3 vitamins were increased specifically in the endosperm through the simultaneous modification of 3 separate metabolic pathways. The transgenic kernels contained 169-fold the normal amount of ␤-carotene, 6-fold the normal amount of ascorbate, and double the normal amount of folate. Levels of engineered vitamins remained stable at least through to the T3 homozygous generation. This achievement, which vastly exceeds any realized thus far by conventional breeding alone, opens the way for the development of nutritionally complete cereals to benefit the world's poorest people.folic acid ͉ metabolic engineering ͉ transgenic maize ͉ vitamin A fortification ͉ vitamin C

Combinatorial nuclear transformation is a novel method for the rapid production of multiplex-transgenic plants, which we have used to dissect and modify a complex metabolic pathway. To demonstrate the principle, we transferred 5 carotenogenic genes controlled by different endosperm-specific promoters into a white maize variety deficient for endosperm carotenoid synthesis. We recovered a diverse population of transgenic plants expressing different enzyme combinations and showing distinct metabolic phenotypes that allowed us to identify and complement rate-limiting steps in the pathway and to demonstrate competition between ␤-carotene hydroxylase and bacterial ␤-carotene ketolase for substrates in 4 sequential steps of the extended pathway. Importantly, this process allowed us to generate plants with extraordinary levels of ␤-carotene and other carotenoids, including complex mixtures of hydroxycarotenoids and ketocarotenoids. Combinatorial transformation is a versatile approach that could be used to modify any metabolic pathway and pathways controlling other biochemical, physiological, or developmental processes.induced mutation ͉ metabolic engineering ͉ transgenic plant ͉ provitamin A