One of the most powerful techniques for attributing functions to genes in uni-and multicellular organisms is comprehensive analysis of mutant traits. In this study, systematic and quantitative analyses of mutant traits are achieved in the budding yeast Saccharomyces cerevisiae by investigating morphological phenotypes. Analysis of fluorescent microscopic images of triple-stained cells makes it possible to treat morphological variations as quantitative traits. Deletion of nearly half of the yeast genes not essential for growth affects these morphological traits. Similar morphological phenotypes are caused by deletions of functionally related genes, enabling a functional assignment of a locus to a specific cellular pathway. The high-dimensional phenotypic analysis of defined yeast mutant strains provides another step toward attributing gene function to all of the genes in the yeast genome.cell morphology ͉ functional genomics ͉ high-dimensional phenotyping ͉ phenome O ne of the ultimate goals of genetics is to reveal relationships between gene function and phenotypic traits. Comprehensive analysis of mutant traits is a very powerful technique for attributing functions to genes in uni-and multicellular organisms. In the budding yeast Saccharomyces cerevisiae, a complete set of mutants, each of which carries a precise deletion of one yeast ORF, has been systematically constructed (1). By using these mutant strains combined with microarray and robot technology, genome-wide analyses of various mutant traits, including general growth rate, fitness under a particular condition, and sensitivity to drugs, has been reported (reviewed in ref. 2).Cell morphology becomes an attractive target for comprehensive analysis, because more powerful methods for fluorescent microscopic imaging analysis in biological research have been emerging after development of high-resolution microscopes and specific fluorescent dyes. Yeast cell morphology reflects various cellular events, including progression through the cell cycle, establishment of cell polarity, and regulation of cell size control. Previous genome-wide studies of yeast morphology were focused on a specific morphology, such as cell size, cell shape, or bud site pattern (3-6), and therefore extracted limited information. Because morphological traits are often judged ''by eye,'' it has remained difficult to obtain quantitative and reproducible results.We recently developed an image-processing system that automatically processes digital cell images of each yeast cell (7,8) to obtain quantitative morphological data of yeast mutant cells. Mannoprotein (as a cell wall component marker), the actin cytoskeleton, and nuclear DNA are specifically stained simultaneously. Cells are then photographed, and fluorescence images are automatically processed. The obtained images of all yeast mutants and data-mining functions are available at our Saccharomyces cerevisiae Morphological Database (SCMD) web site (8,9).In this study, we employ high-dimensional and quantitative phenotyping of yeast muta...
When the rhizosphere is nitrogen-starved, legumes and rhizobia (soil bacteria) enter into a symbiosis that enables the fixation of atmospheric dinitrogen. This implies a complex chemical dialogue between partners and drastic changes on both plant roots and bacteria. Several recent works pointed out the importance of rhizobial surface polysaccharides in the establishing of the highly specific symbiosis between symbionts. Exopolysaccharides appear to be essential for the early infection process. Lipopolysaccharides exhibit specific roles in the later stages of the nodulation processes such as the penetration of the infection thread into the cortical cells or the setting up of the nitrogen-fixing phenotype. More generally, even if active at different steps of the establishing of the symbiosis, all the polysaccharide classes seem to be involved in complex processes of plant defense inhibition that allow plant root invasion. Their chemistry is important for structural recognition as well as for physico-chemical properties.
Exopolysaccharides (EPSs) and K polysaccharides (K-antigens, capsular polysaccharides, or KPSs) are important for the recognition of the symbiotic partner and the infection process, whereas lipopolysaccharides (LPSs) may function at a later stage of symbiosis. Recently, considerable progress has been made in the structural investigation of rhizobial K-antigens and LPSs. This structural data, together with the availability of more and more mutant data, allows new insights into the structure-function relationships of surface polysaccharides and the mode of their action on host cells. This review focuses on rhizobial LPSs and K-antigens. It gives a condensed overview of the recent developments in analysis of their structures and roles during symbiosis.
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