Nitric oxide (NO) is a double-edged sword - it can be either beneficial and activate defence responses in plants and animals or, together with reactive oxygen species, it can kill not only the pathogen but also the host. A prime target of NO is the cytochrome c-dependent respiration. Only plants possess alternative-pathway respiration with alternative oxidase (AOX) as a terminal electron acceptor. AOX has been suggested to be barely affected by NO. Here we show that NO affects cytochrome-dependent respiration in Arabidopsis thaliana (L.) Heynh. At the same time, treatment of Arabidopsis cell cultures with NO actually strongly induced AOX1a transcription, as determined by using a cDNA microarray and by Northern analysis. In accordance with transcript accumulation, NO treatment of suspension cells resulted in increased respiration through the alternative pathway. Addition of an AOX inhibitor to Arabidopsis cell cultures resulted in dramatically increased NO-sensitivity and cell death. In all, our data suggest that NO induces the AOX1a gene and that AOX may participate to counteract the toxicity of NO. Electronic supplementary material to this paper can be obtained by using the Springer Link server located at http://dx.doi.org/10.1007/s00425-002-0828-z.

Nitric oxide (NO) has been associated with plant defense responses during microbial attack, and with induction and/or regulation of programmed cell death. Here, we addressed whether NO participates in wound responses in Arabidopsis thaliana (L.) Heynh. Real-time imaging by confocal laser-scanning microscopy in conjunction with the NO-selective fluorescence indicator 4,5-diaminofluorescein diacetate (DAF-2 DA) uncovered a strong NO burst after wounding or after treatment with JA. The NO burst was triggered within minutes, reminiscent of the oxidative burst during hypersensitive responses. Furthermore, we were able to detect NO in plants (here induced by wounding) by means of electron paramagnetic resonance measurements using diethyldithiocarbamate as a spin trap. When plants were treated with NO, Northern analyses revealed that NO strongly induces key enzymes of jasmonic acid (JA) biosynthesis such as allene oxide synthase (AOS) and lipoxygenase (LOX2). On the other hand, wound-induced AOS gene expression was independent of NO. Furthermore, JA-responsive genes such as defensin (PDF1.2) were not induced, and NO induction of JA-biosynthesis enzymes did not result in elevated levels of JA. However, treatment with NO resulted in accumulation of salicylic acid (SA). In transgenic NahG plants (impaired in SA accumulation and/or signaling), NO did induce JA production and expression of JA-responsive genes. Altogether, the presented data demonstrate that wounding in Arabidopsis induces a fast accumulation of NO, and that NO may be involved in JA-associated defense responses and adjustments.

The root is the first plant organ to get in contact with the toxin cadmium (Cd), which is a widespread soil contaminant. Cd inhibits the growth of the primary root, but the mechanisms underlying this inhibition remain elusive. In this study, we used physiological, pharmacological and genetic approaches to investigate the roles of nitric oxide (NO) and auxin in Cd-mediated inhibition of Arabidopsis thaliana root meristem growth. Our study demonstrated that in the first 12 h of exposure, Cd inhibits primary root elongation through a decrease in the sizes of both the elongation and meristematic zones. Following Cd exposure, a decrease in auxin levels is associated with reduced PIN1/3/7 protein accumulation, but not with reduced PIN1/3/7 transcript levels. Additionally, Cd stabilized AXR3/IAA17 protein to repress auxin signalling in this Cd-mediated process. Furthermore, decreasing Cd-induced NO accumulation with either NO-specific scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) or NO synthase inhibitor N(ω) -nitro-l-Arg-methylester (l-NAME) compromised the Cd-mediated inhibition of root meristem development, reduction in auxin and PIN1/3/7 accumulation, as well as stabilization of AXR3/IAA17, indicating that NO participates in Cd-mediated inhibition of root meristem growth. Taken together, our data suggest that Cd inhibits root meristem growth by NO-mediated repression of auxin accumulation and signalling in Arabidopsis.

The rhl quorum-sensing (QS) system plays critical roles in the pathogenesis of P. aeruginosa. However, the regulatory effects that occur directly upstream of the rhl QS system are poorly understood. Here, we show that deletion of gene encoding for the two-component sensor BfmS leads to the activation of its cognate response regulator BfmR, which in turn directly binds to the promoter and decreases the expression of the rhlR gene that encodes the QS regulator RhlR, causing the inhibition of the rhl QS system. In the absence of bfmS, the Acka-Pta pathway can modulate the regulatory activity of BfmR. In addition, BfmS tunes the expression of 202 genes that comprise 3.6% of the P. aeruginosa genome. We further demonstrate that deletion of bfmS causes substantially reduced virulence in lettuce leaf, reduced cytotoxicity, enhanced invasion, and reduced bacterial survival during acute mouse lung infection. Intriguingly, specific missense mutations, which occur naturally in the bfmS gene in P. aeruginosa cystic fibrosis (CF) isolates such as DK2 strains and RP73 strain, can produce BfmS variants (BfmSL181P, BfmSL181P/E376Q, and BfmSR393H) that no longer repress, but instead activate BfmR. As a result, BfmS variants, but not the wild-type BfmS, inhibit the rhl QS system. This study thus uncovers a previously unexplored signal transduction pathway, BfmS/BfmR/RhlR, for the regulation of rhl QS in P. aeruginosa. We propose that BfmRS TCS may have an important role in the regulation and evolution of P. aeruginosa virulence during chronic infection in CF lungs.

Hevea brasiliensis, being the only source of commercial natural rubber, is an extremely economically important crop. In an effort to facilitate biological, biochemical and molecular research in rubber biosynthesis, here we report the use of next-generation massively parallel sequencing technologies and de novo transcriptome assembly to gain a comprehensive overview of the H. brasiliensis transcriptome. The sequencing output generated more than 12 million reads with an average length of 90 nt. In total 48,768 unigenes (mean size = 436 bp, median size = 328 bp) were assembled through de novo transcriptome assembly. Out of 13,807 H. brasiliensis cDNA sequences deposited in Genbank of the National Center for Biotechnology Information (NCBI) (as of Feb 2011), 11,746 sequences (84.5%) could be matched with the assembled unigenes through nucleotide BLAST. The assembled sequences were annotated with gene descriptions, Gene Ontology (GO) and Clusters of Orthologous Group (COG) terms. In all, 37,432 unigenes were successfully annotated, of which 24,545 (65.5%) aligned to Ricinus communis proteins. Furthermore, the annotated uingenes were functionally classified according to the GO, COG and Kyoto Encyclopedia of Genes and Genomes databases. Our data provides the most comprehensive sequence resource available for the study of rubber trees as well as demonstrates effective use of Illumina sequencing and de novo transcriptome assembly in a species lacking genomic information.

Due to its high reactivity and its ability to diffuse and permeate the cell membrane, nitric oxide (NO) and its exchangeable redox-activated species are unique biological messengers in animals and in plants. Although an increasing number of reports indicate that NO is an essential molecule in several physiological processes, there is not a clear picture of its method of action. Studies on the transcriptional changes induced by NO permitted identification of genes involved in different functional processes such as signal transduction, defence and cell death, transport, basic metabolism, and reactive oxygen species (ROS) production and degradation. The co-expression of these genes can be explained by the co-operation of a set of transcription factors that bind a common region in the promoter of the regulated genes. The present report describes the search for a common transcription factor-binding site (TFBS) in promoter regions of NO-regulated genes, based on microarray analyses. Using Genomatix Gene2Promotor and MatInspector, eight families of TFBSs were found to occur at least 15% more often in the promoter regions of the responsive genes in comparison with the promoter regions of 28,447 Arabidopsis control genes. Most of these TFBSs, such as ocs element-like sequences and WRKY, have already been reported to be involved in particular stress responses. Furthermore, the promoter regions of genes involved in jasmonic acid (JA) biosynthesis were analysed for a common TFBS module, since some genes responsible for JA biosynthesis are induced by NO, and an interaction between NO and JA signalling has already been described.

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In this study, one rice population of recombinant inbred lines (RILs) was used to determine the genetic characteristics of seed reserve utilization during the early (day 6), middle (day 10) and late (day 14) germination stages. The seedling dry weight (SDW) and weight of the mobilized seed reserve (WMSR) were increased, while the seed reserve utilization efficiency (SRUE) decreased, during the process of seed germination. The SDW and WMSR were affected by the seed weight, while the SRUE was not affected by the seed weight. A total of twenty unconditional and twenty-one conditional additive QTLs and eight epistatic QTLs were identified at three germination stages, and the more QTLs were expressed at the late germination stage. Among them, twelve additive and three epistatic QTLs for SDW, eight additive and three epistatic QTLs for WMSR and thirteen additive and two epistatic QTLs for SRUE were identified, respectively. The phenotypic variation explained by each additive QTL, epistatic QTL and QTL × development interaction ranged from 6.10 to 23.91%, 1.79 to 6.88% and 0.22 to 2.86%, respectively. Two major additive QTLs qWMSR7.1 and qSRUE4.3 were identified, and each QTL could explain more than 20% of the total phenotypic variance. By comparing the chromosomal positions of these additive QTLs with those previously identified, eleven QTLs might represent novel genes. The best four cross combinations of each trait for the development of RIL populations were selected. The selected RILs and the identified QTLs might be applicable to improve rice seed reserve utilization by the marker-assisted selection approach.