Production of the Cancer-Preventive Glucoraphanin in Tobacco

Epidemiological studies have demonstrated reduced risk of developing cancer upon consumption of diets rich in cruciferous vegetables. This chemoprevention has been largely attributed to the presence of the natural products glu- cosinolates, particularly the methionine-derived glucoraphanin from broccoli. Improved nutrition by functional foods or health-promoting dietary supplements is an attractive means for prevention of lifestyle-based diseases. Towards this goal, we have engineered the glucoraphanin pathway into tobacco. First, we engineered elongation of the side chain of methionine to produce the key intermediate dihomo-methionine. This process is catalyzed through two cycles in a chain-elongation pathway that takes place partly in the cytosol and partly in the chloroplast. Second, by coupling the five enzymes of the chain-elongation pathway to eight enzymes of the glucosinolate pathway, we show production of glucoraphanin together with other glucosinolates derived from chain-elongated isoleucine and/or leucine. The conver- sion of methionine to glucoraphanin is obtained via 14 intermediates. Demonstrating the production of the high-value glucoraphanin in a heterologous host has great potential in the food and medicinal industry as a means to generate a stable, rich source of glucoraphanin for the benefit of human health.

Coronatine-lnsensitive 1 （COI1） Mediates Transcriptional Responses of Arabidopsis thaliana to External Potassium Supply

The ability to adjust growth and development to the availability of mineral nutrients in the soil is an essential life skill of plants but the underlying signaling pathways are poorly understood. In Arab/dops/s thal/ana, shortage of po- tassium （K） induces a number of genes related to the phytohormone jasmonic acid （JA）. Using comparative microarray analysis of wild-type and coi1-16 mutant plants, we classified transcriptional responses to K with respect to their depen- dence on COI1, a central component of oxylipin signaling. Expression profiles obtained in a short-term experiment clearly distinguished between COil-dependent and COil-independent K-responsive genes, and identified both known and novel targets of JA-COIl-signaling. During long-term K-deficiency, coi-16 mutants displayed de novo responses covering similar functions as COil-targets except for defense. A putative role of JA for enhancing the defense potential of K-deficient plants was further supported by the observation that plants grown on low K were less damaged by thrips than plants grown with sufficient K.

Metabolomic, Transcriptional, Hormonal, and Signaling Cross-Talk in Superroot2

Auxin homeostasis is pivotal for normal plant growth and development. The superroot2 （sur2） mutant was initially isolated in a forward genetic screen for auxin overproducers, and SUR2 was suggested to control auxin conju- gation and thereby regulate auxin homeostasis. However, the phenotype was not uniform and could not be described as a pure high auxin phenotype, indicating that knockout of CYP83B1 has multiple effects. Subsequently, SUR2 was identified as CYP83B1, a cytochrome P450 positioned at the metabolic branch point between auxin and indole glucosinolate metabolism. To investigate concomitant global alterations triggered by knockout of CYP83B1 and the countermeasures chosen by the mutant to cope with hormonal and metabolic imbalances, 10-day-old mutant seedlings were characterized with respect to their transcriptome and metabolome profiles. Here, we report a global analysis of the sur2 mutant by the use of a combined transcriptomic and metabolomic approach revealing pronounced effects on several metabolic grids including the intersection between secondary metabolism, cell wall turnover, hormone metabolism, and stress responses. Metabolic and transcriptional cross-talks in sur2 were found to be regulated by complex interactions between both positively and negatively acting transcription factors. The complex phenotype of sur2 may thus not only be assigned to elevated levels of auxin, but also to ethylene and abscisic acid responses as well as drought responses in the absence of a water deficiency. The delicate balance between these signals explains why minute changes in growth conditions may result in the non-uniform phenotype. The large phenotypic variation observed between and within the different surveys may be reconciled by the complex and intricate hormonal balances in sur2 seedlings decoded in this study.