Jorn Gorlach

Growth Stage–Based Phenotypic Analysis of Arabidopsis: A Model for High Throughput Functional Genomics in Plants

With the completion of the Arabidopsis genome sequencing project, the next major challenge is the large-scale determination of gene function. As a model organism for agricultural biotechnology, Arabidopsis presents the opportunity to provide key insights into the way that gene function can affect commercial crop production. In an attempt to aid in the rapid discovery of gene function, we have established a high throughput phenotypic analysis process based on a series of defined growth stages that serve both as developmental landmarks and as triggers for the collection of morphological data. The data collection process has been divided into two complementary platforms to ensure the capture of detailed data describing Arabidopsis growth and development over the entire life of the plant. The first platform characterizes early seedling growth on vertical plates for a period of 2 weeks. The second platform consists of an extensive set of measurements from plants grown on soil for a period of ∼2 months. When combined with parallel processes for metabolic and gene expression profiling, these platforms constitute a core technology in the high throughput determination of gene function. We present here analyses of the development of wild-type Columbia (Col-0) plants and selected mutants to illustrate a framework methodology that can be used to identify and interpret phenotypic differences in plants resulting from genetic variation and/or environmental stress.

Benzothiadiazole, a novel class of inducers of systemic acquired resistance, activates gene expression and disease resistance in wheat.

Systemic acquired resistance is an important component of the disease resistance repertoire of plants. In this study, a novel synthetic chemical, benzo(1,2,3)thiadiazole-7-carbothioic acid S-methyl ester (BTH), was shown to induce acquired resistance in wheat. BTH protected wheat systemically against powdery mildew infection by affecting multiple steps in the life cycle of the pathogen. The onset of resistance was accompanied by the induction of a number of newly described wheat chemically induced (WCI) genes, including genes encoding a lipoxygenase and a sulfur-rich protein. With respect to both timing and effectiveness, a tight correlation existed between the onset of resistance and the induction of the WCI genes. Compared with other plant activators, such as 2,6-dichloroisonicotinic acid and salicylic acid, BTH was the most potent inducer of both resistance and gene induction. BTH is being developed commercially as a novel type of plant protection compound that works by inducing the plants inherent disease resistance mechanisms.

Wheat Genes Encoding Two Types of PR-1 Proteins Are Pathogen Inducible, but Do Not Respond to Activators of Systemic Acquired Resistance

Wheat cDNAs that encode proteins PR-1.1 and PR-1.2 were cloned. Deduced amino acid sequences were homologous to those of pathogen-induced, basic PR-1 proteins from plants. Although expression of PR1.1 and PR1.2 genes was induced upon infection with either compatible or incompatible isolates of the fungal pathogen Erysiphe graminis, these genes did not respond to activators of systemic acquired resistance (SAR), such as salicylic acid (SA), benzothiadiazole (BTH), or isonicotinic acid (INA).

Mechanosensitive Expression of a Lipoxygenase Gene in Wheat

Touch stimulation of wheat (Triticum aestivum L.) seedlings led to a strong and dose-dependent increase in the level of lipoxygenase mRNA transcripts. The touch-induced response occurred within 1 h and was transient. A similar response was observed after wind treatment and wounding. The mechanical strain-regulated lipoxygenase might translate mechanical strain into lipoxygenase pathway-dependent growth responses.

Plastidic Isoprenoid Synthesis Changes from an Autonomous to a Division-of-Labor Stage During Chloroplast Maturation

Carotenoids, plastoquinone, tocopherols and the phytyl moiety of Chlorophyll are generally known as isoprenoids synthesized in the chloroplast. The origin of IPP to form these plastidic compounds is, however, still under debate. We are able to demonstrate that the basal region of leaves from 10-d old barley seedlings containing developing chloroplasts forms plastidic isoprenoids predominantly from photosyn-thetically fixed CO2 and only to a lesser extent from added mevalonate (Mev). The conditions totally changes during chloroplast maturation. The ability to form these compounds from CO2 disappears at the apical region of the leaves containing mature chloroplasts. In this region IPP, formed from added Mev, is effectively used for isoprenoid synthesis. Developing and mature chloroplasts isolated from leaf protoplasts conform in behavior with the corresponding leaf regions.