Sucrose starvation of Arabidopsis (Arabidopsis thaliana) cell culture was used to identify translationally regulated genes by DNA microarray analysis. Cells were starved by subculture without sucrose, and total and polysomal RNA was extracted between 6 and 48 h. Probes were derived from both RNA populations and used to screen oligonucleotide microarrays. Out of 25,607 screened genes, 224 were found to be differentially accumulated in polysomal RNA following starvation and 21 were found to be invariant in polysomal RNA while their total RNA abundance was modified. Most of the mRNA appears to be translationally repressed (183/245 genes), which is consistent with a general decrease in metabolic activities during starvation. The parallel transcriptional analysis identifies 268 regulated genes. Comparison of transcriptional and translational gene lists highlights the importance of translational regulation (mostly repression) affecting genes involved in cell cycle and cell growth, these being overrepresented in translationally regulated genes, providing a molecular framework for the arrest of cell proliferation following starvation. Starvation-induced translational control also affects chromatin regulation genes, such as the HD1 histone deacetylase, and the level of histone H4 acetylation was found to increase during starvation. This suggests that regulation of the global nuclear transcriptional activity might be linked to cytoplasmic translational regulations.

Summary BnaGLN1 coding sequences and expression profiles in response to nitrogen availability and ageing are essentially conserved compared with A. thaliana, suggesting that the roles of GLN1 families are conserved among the Brassiceae tribe.

The bacterium Photorhabdus establishes a highly specific association with Heterorhabditis, its nematode host. Photorhabdus strains associated with Heterorhabditis bacteriophora or Heterorhabditis megidis were compared using a Photorhabdus DNA microarray. We describe 31 regions belonging to the Photorhabdus flexible gene pool. Distribution analysis of regions among the Photorhabdus genus identified loci possibly involved in nematode specificity.Photorhabdus is an entomopathogenic gram-negative bacterium belonging to the Enterobacteriaceae. Both Photorhabdus luminescens and Photorhabdus temperata species are symbionts of entomopathogenic Heterorhabditis nematodes (7). Bacterial and nematode taxonomic data reveal a highly specific association between bacterial strains and nematode species. A recently described species, Photorhabdus asymbiotica, was never found to be associated with nematodes but was isolated from human infections (3,12,15,22). Although a few studies have identified several Photorhabdus genes that are required for normal growth and development of the nematode (5, 6, 9, 19, 29), we have little molecular and functional data about the first step of nematode colonization and nematode specificity.The genome sequence of P. luminescens subsp. luminescens strain TT01 revealed a high number of genes encoding proteins potentially involved in host-bacterium interaction (10). This genome also showed an impressive number of mobile or repeated genetic elements (phage remnants, IS, transposons, ERIC elements, and overrepresented families of paralogs). Furthermore, 32 genomic islands (GI) were predicted on the basis of in silico features.The goal of this project was to identify bacterial genomic regions that are possibly involved in nematode specificity. The genomes of two strains harbored by two nematode species, P. luminescens subsp. laumondii TT01, associated with Heterorhabditis bacteriophora, and P. temperata subsp. temperata XlNach, associated with H. megidis, were compared using a Photorhabdus TT01 DNA microarray. Since the TT01 and XlNach strains belonged to different species, genomic differences could depend on the taxonomic difference. In order to avoid this bias, the microarray comparison was also performed between TT01 and the P. temperata C1 strain, which was isolated from an H. bacteriophora nematode (20, 23). The genomic regions present in both TT01 and C1 but that were missing in XlNach were considered potentially specific to strains associated with H. bacteriophora. Photorhabdus strains were stored at Ϫ80°C and grown in Luria-Bertani broth or on 1.5% nutrient agar (Difco) at 28°C. Genomic DNA (gDNA) was extracted according to the method of Brenner et al. (8) and stored at 4°C.The Photorhabdus DNA microarray used in this study is representative of 4,144 genes out of the 4,909 predicted genes of the P. luminescens strain TT01 chromosomal sequence (accession number NC_005126). Paralogous genes (mainly IS and putative phages) were excluded. Primers were designed by use of a modified version of Primer...

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