No abstract

The classic wheat evolutionary history is one of adaptive radiation of the diploid Triticum͞Aegilops species (A, S, D), genome convergence and divergence of the tetraploid (Triticum turgidum AABB, and Triticum timopheevii AAGG) and hexaploid (Triticum aestivum, AABBDD) species. We analyzed Acc-1 (plastid acetyl-CoA carboxylase) and Pgk-1 (plastid 3-phosphoglycerate kinase) genes to determine phylogenetic relationships among Triticum and Aegilops species of the wheat lineage and to establish the timeline of wheat evolution based on gene sequence comparisons.

Anabaena 7120 mutant 216 fails to differentiate heterocysts. We previously identified a 2.4-kb wild-type DNA fragment able to complement this mutant. We show here that the sequence of this fragment contains a single open reading frame [hetR), encoding a 299-amino-acid protein. Conjugation of deletion subclones of this fragment into strain 216 showed that the /ieti?-coding region is both necessary and sufficient for complementation of the Het~ phenotype. The mutation in 216 is located at nucleotide 535 in the betR gene, converting a serine at position 179 in the wild-type protein to an asparagine in the mutant. Interruption of the hetR gene in wild-type cells results in a mutant phenotype identical to that of 216. Both 216 and wild-type cells containing wild-type hetR on a plasmid display increased frequency of heterocysts, even on media containing fixed nitrogen. These results suggest that hetR encodes a product that is not only essential for but also controls heterocyst development. This putative regulatory protein lacks known structural motifs characteristic of transcription factors and probably acts at a level one or more steps removed from its target genes.

Brucella melitensis is a facultative intracellular bacterial pathogen that causes abortion in goats and sheep and Malta fever in humans. The genome of B. melitensis strain 16M was sequenced and found to contain 3,294,935 bp distributed over two circular chromosomes of 2,117,144 bp and 1,177,787 bp encoding 3,197 ORFs. By using the bioinformatics suite ERGO, 2,487 (78%) ORFs were assigned functions. The origins of replication of the two chromosomes are similar to those of other ␣-proteobacteria. Housekeeping genes, including those involved in DNA replication, transcription, translation, core metabolism, and cell wall biosynthesis, are distributed on both chromosomes. Type I, II, and III secretion systems are absent, but genes encoding sec-dependent, sec-independent, and flagellaspecific type III, type IV, and type V secretion systems as well as adhesins, invasins, and hemolysins were identified. Several features of the B. melitensis genome are similar to those of the symbiotic Sinorhizobium meliloti.