Asr Gene Research Articles

Transcriptional analysis of the acid-inducible asr gene in enterobacteria

We show here that transcription of the asr gene in Escherichia coli, Salmonella enterica serovar Typhimurium, Klebsiella pneumoniae and Enterobacter cloacae is strongly dependent on the acidification level of the growth medium, with maximal induction at pH 4.0–4.5 as determined by Northern hybridization analysis. Previous gene array analyses have also shown that asr is the most acid-induced gene in the E. coli genome. Sequence alignment of the asr promoters from different enterobacterial species identified a highly conserved region located at position −70 to −30 relative to the asr transcriptional start site. By deletion of various segments of this region in the E. coli asr promoter it was shown that sequences upstream from the −40 position were important for induction. Transcription from the E. coli asr promoter was demonstrated to be growth-phase-dependent and to require the alternative sigma factor RpoS (σ S) in stationary phase. Transcription of the asr gene was also found to be subject to negative control by the nucleoid protein HNS.

Differential expression of the members of the Asr gene family in tomato ( Lycopersicon esculentum)

In this work, we continued to dissect the Asr (ABA/water stress/ripening-induced) gene family originally described in tomato. A RT-PCR-based strategy was developed to assess the organ (leaf, root and fruit) and developmental (immature and ripe fruit) specificity of expression of the three known members of the Asr gene family under normal and stress conditions. Our results allow us to conclude that whereas Asr1 and Asr2 are the members of the family preferentially induced by desiccation in leaves, Asr2 is the only one activated in the roots from water-deficit-stressed plants. We also observed that expression of the three genes does not change significantly in fruit at different developmental stages, except for that of Asr2, which decreases after the breaker yellow stage. In addition, we identified a 72-amino acid polar peptide region, rich in His, Lys, Glu and Ala, which contains two internal imperfect repeats and is highly conserved in more recently discovered Asr-like proteins from other plant species exposed to different kinds of abiotic stress such as water deficit, salt, cold and/or limiting amount of light.

Characterization and expression pattern of an abscisic acid and osmotic stress responsive gene from rice

Identification and characterization of salt responsive genes is an initial step in understanding the adaptive responses to salinity. We report the characterization and expression pattern of an abscisic acid (ABA) and osmotic stress responsive gene from rice which shows sequence similarity with the Asr (ABA, stress and ripening inducible) genes identified in several species. A partial cDNA for the Oryza sativa Asr1 ( OsAsr1) was identified from a cDNA library constructed from salt stressed tissues of Pokkali, a salt tolerant rice variety by sequence homology. Subsequently, the cDNA encoding the complete polypeptide was cloned by PCR amplification from the same cDNA library. The OsAsr1 sequence encodes a hydrophilic protein with a molecular weight of 15.4 kDa and has the conserved regions of the ASR homologs. OsAsr1 hybridizes to a ∼0.8 kb transcript which is constitutively expressed; its levels in the shoot are up-regulated by exogenous application of ABA and osmotic stress imposed by mannitol and salt. Further, the salt induction is transient, increasing at least up to 6 h and reduced within 24 h of stress. Southern and Blast analysis suggests that the Asr genes form a gene family of at least two members in rice.

Analysis of an abscisic acid (ABA)-responsive gene promoter belonging to the Asr gene family from tomato in homologous and heterologous systems.

Asr is a family of genes that maps to chromosome 4 of tomato. Asr2, a recently reported member of this family, is believed to be regulated by abscisic acid (ABA), stress and ripening. A genomic Asr2 clone has been fully sequenced, and candidate upstream regulatory elements have been identified. To prove that the promoter region is functional in vivo, we fused it upstream of the beta-glucuronidase (GUS) reporter gene. The resulting chimeric gene fusion was used for transient expression assays in papaya embryogenic calli and leaves. In addition, the same construct was used to produce transgenic tomato, papaya, tobacco, and potato plants. Asr2 upstream sequences showed promoter function in all of these systems. Under the experimental conditions tested, ABA stimulated GUS expression in papaya and tobacco, but not in tomato and potato systems.

Asr genes belong to a gene family comprising at least three closely linked loci on chromosome 4 in tomato.

Asr1, Asr2 and Asr3 are three homologous clones isolated from tomato whose expression is believed to be regulated by abscisic acid (ABA); the corresponding genes thus participate in physiological and developmental processes such as responses of leaf and root to water stress, and fruit ripening. In this report, results obtained with Near Isogenic Lines reveal that Asr1, Asr2 and Asr3 represent three different loci. In addition, we map these genes on the restriction fragment length polymorphism (RFLP) map of the tomato genome by using an F2 population derived from an interspecific hybrid cross L. esculentum x L. penelli. RFLP data allow us to map these genes on chromosome 4, suggesting that they belong to a gene family. The elucidation of the genomic organization of the Asr gene family may help in understanding the role of its members in the response to osmotic stress, as well as in fruit ripening, at the molecular level.