Using a radish cDNA probe, we have isolated and characterized two genomic clones from Arabidopsis thaliana (GEA1 and GEA6) encoding two different proteins that are homologous to the "Early methionine-labelled" (Em) protein of wheat. GEA1 differs from GEA6 and Em clones of wheat in that a sequence coding for 20 amino acid residues is tandemly repeated 4 times. These two genomic clones correspond to two genes named AtEm1 and AtEm6. Sequencing of several cDNA clones showed that both genes are expressed. The transcription start site was determined for both genes by RNase mapping. The site of polyadenylation is variable and there is no obvious consensus sequence for polyadenylation at the 3' ends of the genes. mRNA corresponding to GEA6 is present only in nearly dry and dry seeds, whereas the corresponding to GEA1 appears in immature seeds and is maximum in dry seeds. No expression of either gene could be detected in leaf, stem, or floral buds. Expression of both genes could be detected in immature seeds when the siliques were incubated with abscisic acid (ABA), demonstrating that both genes are ABA responsive. However, examination of the 5' upstream region does not reveal any extensive homology, suggesting that regulation of the two genes differs. In situ hybridization with a GEA1 probe demonstrated that the expression of this gene is essentially located in the provascular tissues of the cotyledons and axis of the dry seed as well as in the epiderm and outer layers of the cortex in the embryo axis.

During the course of an Arabidopsis thaliana genome sequencing project, we identified a gene, G4, with a derived amino acid sequence showing homology to the product of the Rhodobacter capsulatus bchG locus which is involved in the esterification of bacteriochlorophyllide with geranylgeraniol. The relationship between this gene and bchG was confirmed by the isolation and analysis of a corresponding full-length cDNA. Comparison of genomic and cDNA sequences indicated that the gene is made up of 14 exons, some of them being very short. Southern and Northern analyses showed that this sequence represents a single-copy gene and its transcript is detected only in green or greening tissues. Both homologies and expression data suggest that this gene encodes a chlorophyll synthetase, one of the last enzymes of chlorophyll biosynthesis, and thus represents a new example of a nuclear gene encoding an enzyme of this pathway in higher plants.

We report the genetic and physical analysis by pulse field gel electrophoresis (PFGE) in three Brassica diploid genomes for a cluster of five genes characterized in a selected segment of 15 kb on chromosome 3 of Arabidopsis thaliana, encoding a Bradyrhizobium CycJ homologue (At1), a rat p67 translation factor homologue (At2), an Em-like (early methionine) protein (At3), chlorophyll synthase (At4) and a yeast Sac1 homologue (A5). The Arabidopsis gene array was found to be conserved on a single linkage group in each of the Brassica genomes. However, partial complexes were found to be duplicated in other chromosome segments on the same or other linkage groups. Some of the At genes, which could not be genetically mapped because of lack of polymorphism, were assigned to their respective linkage groups by physical mapping. The presence of multiple copies of the A. thaliana gene cluster in the three Brassica genomes further establishes their complex nature, which results from extensive duplication and chromosomal rearrangement. In general, genetic distances between the At genes agreed with values expected for the physical distances determined in Brassica.