A nuclear gene, erd1, encoding a chloroplast-targeted Clp protease regulatory subunit homolog is not only induced by water stress but also developmentally up-regulated during senescence in Arabidopsis thaliana

A cDNA, ERD1, isolated from one-hour-dehydrated plants of Arabidopsis thaliana L. encodes a putative protein that is similar to the regulatory ATPase subunit (ClpA) of the Clp protease and contains a putative chloroplast-targeting transit-peptide at the N-terminus. A chimeric gene with the putative plastid-targeting sequence of the erd1 gene fused to the synthetic green-fluorescent protein (sGFP) gene was constructed and introduced into Arabidopsis protoplasts. The N-terminal region of the ERD1 protein directed the sGFP protein into the plastids of the protoplasts, and functioned as a transit peptide. Northern blot analysis indicated that expression of the erd1 gene was induced not only by water stress, such as dehydration and high salinity, but also by natural senescence and dark-induced etiolation. The erd1 gene was not strongly induced by exogenous abscisic acid. A chimeric gene with the 0.9 kb promoter region of the erd1 gene fused to the β-glucuronidase (GUS) reporter gene was constructed, and tobacco plants transformed with the construct. The GUS reporter gene driven by the erd1 promoter was induced by dehydration and high salt stress at significant levels in the transgenic plants. The GUS gene was strongly expressed in older leaves without dehydration, and was induced by dark-induced etiolation. Furthermore, GUS activity was reduced by cytokinin treatment during dark-induced etiolation. These results indicate that expression of the erd1 gene is developmentally up-regulated by senescence as well as by water stress.     

Isolation and characterization of gene encoding G protein α subunit protein responsive to plant hormones and abiotic stresses in Brassica napus

G protein plays an important role in signal pathways and involved in various signal transduction systems in plant. A full-length cDNA encoding a putative G protein α subunit (Gα), designated as BnGA1, was isolated from Brassica napus. The expression of BnGA1 in different B. napus tissues and developmental stags was analyzed using real-time PCR. The results showed that BnGA1 expressed was high in root, cotyledon and shoot apex. Stage expression pattern analysis revealed that BnGA1 expressed strongly at the 7th day, the bolting stage and fruiting stage. In addition, the expression of BnGA1 was analyzed under different concentrations of four plant hormones. The expression of BnGA1 was significantly induced by the high concentrations of abscisic acid (ABA) and brassinosteroid (BR). The expression of BnGA1 was also induced by low gibberellins acid 3 (GA₃) concentrations and higher GA₃ concentrations inhibit the expression of BnGA1. However, the expression of BnGA1 did not significantly regulated by exogenous indole-3-acetic acid (IAA). Moreover, the expression of BnGA1 under different abiotic stresses was analyzed at different time points. The BnGA1 was up-regulated in salt and drought stress and down-regulated in heat and cold stress. These expression results suggested that BnGA1 play an important role in plant hormones signal pathways and BnGA1 may be involved in plant defense system against environmental stresses in B. napus.     

The ybiT Gene of Erwinia chrysanthemi Codes for a Putative ABC Transporter and Is Involved in Competitiveness against Endophytic Bacteria during Infection

We investigated the role in bacterial infection of a putative ABC transporter, designated ybiT, of Erwinia chrysanthemi AC4150. The deduced sequence of this gene showed amino acid sequence similarity with other putative ABC transporters of gram-negative bacteria, such as Escherichia coli and Pseudomonas aeruginosa, as well as structural similarity with proteins of Streptomyces spp. involved in resistance to macrolide antibiotics. The gene contiguous to ybiT, designated as pab (putative antibiotic biosynthesis) showed sequence similarity with Pseudomonas and Streptomyces genes involved in the biosynthesis of antibiotics. A ybiT mutant (BT117) was constructed by marker exchange. It retained full virulence in potato tubers and chicory leaves, but it showed reduced ability to compete in planta against the wild-type strain or against selected saprophytic bacteria. These results indicate that the ybiT gene plays a role in the in planta fitness of the bacteria.     

Identification and characterization of genes regulated by AqsR, a LuxR-type regulator in Acinetobacter oleivorans DR1

The complete genome of Acinetobacter oleivorans DR1 contains AqsR and AqsI genes, which are LuxR and LuxI homolog, respectively. In a previous study, we demonstrated that quorum sensing (QS) signals play an important role in biofilm formation and hexadecane biodegradation. However, the regulation of genes controlled by the QS system in DR1 remains unexplored. We constructed an aqsR mutant and performed RNA sequencing analysis to understand the QS system. A total of 353 genes were differentially expressed during the stationary phase of wild-type cells compared to that of the aqsR mutant. AqsR appears to be an exceptionally important regulator because knockout of aqsR affected global gene expression. Genes involved in posttranslational modification, chaperones, cell wall structure, secondary metabolites biosynthesis, and stress defense were highly upregulated only in the wild type. Among upregulated genes, both the AOLE_03905 (putative surface adhesion protein) and the AOLE_11355 (L-asparaginase) genes have putative LuxR binding sites at their promoter regions. Soluble AqsR proteins were successfully purified in Escherichia coli harboring both aqsR and aqsI. Comparison of QS signals in an AqsI–AqsR co-overexpression strain with N-acyl homoserine lactone standards showed that the cognate N-acyl homoserine lactone binding to AqsR might be 3OH C12HSL. Our electrophoretic mobility shift assays with purified AqsR revealed direct binding of AqsR to those promoter regions. Our data showed that AqsR functions as an important regulator and is associated with several phenotypes, such as hexadecane utilization, biofilm formation, and sensitivity to cumene hydroperoxide.     

The Saccharomyces cerevisiae SGE1 gene product: a novel drug-resistance protein within the major facilitator superfamily

Several pleiotropic drug sensitivities have been described in yeast. Some involve the loss of putative drug efflux pumps analogous to mammalian P-glycoproteins, others are caused by defects in sterol synthesis resulting in higher plasma membrane permeability. We have constructed a Saccharomyces cerevisiae strain that exhibits a strong crystal violet-sensitive phenotype. By selecting cells of the supersensitive strain for normal sensitivity after transformation with a wild-type yeast genomic library, a complementing 10-kb DNA fragment was isolated, a 3.4-kb subfragment of which was sufficient for complementation. DNA sequence analysis revealed that the complementing fragment comprised the recently sequenced SGE1 gene, a partial multicopy suppressor of gal11 mutations. The supersensitive strain was found to be a sge1 null mutant. Overexpression of SGE1 on a high-copy-number plasmid increased the resistance of the supersensitive strain. Disruption of SGE1 in a wild-type strain increased the sensitivity of the strain. These features of the SGE1 phenotype, as well as sequence homologies of SGE1 at the amino acid level, confirm that the Sge1 protein is a member of the drug-resistance protein family within the major facilitator superfamily (MFS).     

Mildew Resistance Locus O Gene Cloning,Characterization, and Expression Pattern in Mulberry (<Emphasis Type="Italic">Morus multicaulis</Emphasis>) and Its Prokaryotic Expression in <Emphasis Type="Italic">E. coli</Emphasis>

MLO (mildew resistance locus O), which encodes a transmembrane protein 7TM, is considered to be a model plant gene suitable for studying broad-spectrum resistance. It is a negative regulator of powdery mildew resistance and thus has potential applications in plant breeding. In the present paper, a full cDNA sequence encoding MLO was cloned from the leaves of mulberry (Morus multicaulis) based on mulberry expressed sequence tags (EST), homologous cloning technology, and 5′-RLM-RACE using RT-PCR;the sequence was designated MMLO (GenBank accession no. KX683296). The full cDNA was 1943 bp in length with 5′-untranslated region (UTR) of 106 bp, 3′-UTR of 160 bp, and an open reading frame (ORF) of 1677 bp encoding a protein of 558 amino acids. The estimated molecular weight and isoelectric point (pI) of the putative protein were 62.48 kDa and 9.03, respectively. The MMLO protein had Mlo domain and belonged to the Mlo superfamily. Phylogenetic analysis based on the amino acid sequences encoded by the MLO gene from various species showed that mulberry was closely related to Eucalyptus grandis, Ziziphus jujube, and Juglansregia. Quantitative real-time PCR (qRT-PCR) analysis revealed that MMLO was expressed in all the tissues tested, including leaf, bud, fruit, stem, phloem, and xylem in mulberry with the highest expression in the phloem. The expression level of the mRNA increased and significantly changed under drought, cold, and salt stress treatments compared to the normal growth environment. The ORF segment of the MMLO was inserted into the expression plasmid pET-28a(+) to construct a recombinant expression plasmid. SDS-PAGE result revealed that fusion protein was successfully expressed. Overall, these results provide a better understanding of the molecular basis for the signal transduction mechanism during the stress responses in mulberry trees.     

Expression patterns of a cinnamyl alcohol dehydrogenase gene involved in lignin biosynthesis and environmental stress in Ginkgo biloba

The cinnamyl alcohol dehydrogenase (CAD) is a key enzyme in lignin biosynthesis as it catalyzes the final step in the synthesis of monolignols. A cDNA sequence encoding the CAD gene was isolated from the leaves of Ginkgo biloba L, designated as GbCAD1. The full-length cDNA of GbCAD1 was 1,494?bp containing a 1,074?bp open reading frame encoding a polypeptide of 357 amino acids with a calculated molecular mass of 38.7?kDa and an isoelectric point of 5.74. Comparative and bioinformatic analyses revealed that GbCAD1 showed extensive homology with CADs from other gymnosperm species. Southern blot analysis indicated that GbCAD1 belonged to a multi-gene family. Phylogenetic tree analysis revealed that GbCAD1 shared the same ancestor in evolution with other CADs and had a further relationship with other gymnosperm species. GbCAD1 was an enzyme being pH-dependent and temperature-sensitive, and showing a selected catalyzing. Tissue expression pattern analysis showed that GbCAD1 was constitutively expressed in stems and roots, especially in the parts of the pest and disease infection, with the lower expression being found in two- to four-year-old stem. Further analysis showed the change in lignin content had some linear correlation with the expression level of GbCAD1 mRNA in different tissues. The increased expression of GbCAD1 was detected when the seedling were treated with exogenous abscisic acid, salicylic acid, ethephon, ultraviolet and wounding. These results indicate that the GbCAD1 gene may play a role in the resistance mechanism to biotic and abiotic stresses as well as in tissue-specific developmental lignification.