Unified display of Arabidopsis thaliana physical maps from AtDB, the A.thaliana database.

In the past several years, there has been a tremendous effort to construct physical maps and to sequence the genome of Arabidopsis thaliana. As a result, four of the five chromosomes are completely covered by overlapping clones except at the centromeric and nucleolus organizer regions (NOR). In addition, over 30% of the genome has been sequenced and completion is anticipated by the end of the year 2000. Despite these accomplishments, the physical maps are provided in many formats on laboratories' Web sites. These data are thus difficult to obtain in a coherent manner for researchers. To alleviate this problem, AtDB (Arabidopsis thaliana DataBase, URL: http://genome-www.stanford.edu/Arabidopsis/) has constructed a unified display of the physical maps where all publicly available physical-map data for all chromosomes are presented through the Web in a clickable, 'on-the-fly' graphic, created by CGI programs that directly consult our relational database.

Construction of an approximately 2 Mb contig in the region around 80 cM of Arabidopsis thaliana chromosome 2.

A method for construction of bacterial artificial chromosome (BAC) contigs from a yeast artificial chromosome (YAC) physical map is described. An approximately 2 Mb contig, consisting of two large BAC contigs linked by a small YAC, has been assembled in the region around 80 cM of Arabidopsis thaliana chromosome 2. Clones from this contig will facilitate gene isolation in the region and can be used directly as substrates for DNA sequencing.

The liguleless-1 gene acts tissue specifically in maize leaf development.

The liguleless-1 (lg1) gene affects maize leaf development. In a normal maize leaf, a ligule and auricles separate the blade and sheath. The recessive lg1 mutation prevents formation of ligules and auricles during leaf development. To determine the timing and site of lg1 gene action, we compared development of wild-type and lg1 mutant leaves, and analyzed genetic mosaics composed of wild-type and lg1 mutant cells. In wild-type leaves the first sign of differentiation of the ligular region is a series of specialized anticlinal divisions in the adaxial epidermis. This establishes a distinct band of cells, from which the ligule arises via periclinal divisions. The anticlinal divisions preceding ligule formation are altered in the mutant; therefore, the gene acts early in development, before the periclinal divisions, and possibly during basipetal vascularization. Genetic mosaic analysis indicates that the lg1 gene has at least two functions with different tissue specificities: The Lg1+ wild-type allele acts autonomously in the adaxial epidermis for normal ligule development, and in internal tissues for auricle formation. Wild-type internal tissue in direct contact with lg1 epidermis appears able to induce the mutant epidermis to form a rudimentary ligule. The results indicate that the lg1 gene acts tissue specifically in an early step of ligule and auricle initiation.