The Arabidopsis translocator protein (AtTSPO) is regulated at multiple levels in response to salt stress and perturbations in tetrapyrrole metabolism

<p>Abstract</p> <p>Background</p> <p>The translocator protein 18 kDa (TSPO), previously known as the peripheral-type benzodiazepine receptor (PBR), is important for many cellular functions in mammals and bacteria, such as steroid biosynthesis, cellular respiration, cell proliferation, apoptosis, immunomodulation, transport of porphyrins and anions. <it>Arabidopsis thaliana </it>contains a single <it>TSPO/PBR</it>-related gene with a 40 amino acid N-terminal extension compared to its homologs in bacteria or mammals suggesting it might be chloroplast or mitochondrial localized.</p> <p>Results</p> <p>To test if the TSPO N-terminal extension targets it to organelles, we fused three potential translational start sites in the <it>TSPO </it>cDNA to the N-terminus of GFP (<it>At</it>TSPO:eGFP). The location of the <it>At</it>TSPO:eGFP fusion protein was found to depend on the translational start position and the conditions under which plants were grown. Full-length <it>At</it>TSPO:eGFP fusion protein was found in the endoplasmic reticulum and in vesicles of unknown identity when plants were grown in standard conditions. However, full length <it>At</it>TSPO:eGFP localized to chloroplasts when grown in the presence of 150 mM NaCl, conditions of salt stress. In contrast, when <it>At</it>TSPO:eGFP was truncated to the second or third start codon at amino acid position 21 or 42, the fusion protein co-localized with a mitochondrial marker in standard conditions. Using promoter <it>GUS </it>fusions, qRT-PCR, fluorescent protein tagging, and chloroplast fractionation approaches, we demonstrate that <it>At</it>TSPO levels are regulated at the transcriptional, post-transcriptional and post-translational levels in response to abiotic stress conditions. Salt-responsive genes are increased in a <it>tspo-1 knock-down </it>mutant compared to wild type under conditions of salt stress, while they are decreased when <it>At</it>TSPO is overexpressed. Mutations in tetrapyrrole biosynthesis genes and the application of chlorophyll or carotenoid biosynthesis inhibitors also affect <it>AtTSPO </it>expression.</p> <p>Conclusion</p> <p>Our data suggest that AtTSPO plays a role in the response of <it>Arabidopsis </it>to high salt stress. Salt stress leads to re-localization of the AtTSPO from the ER to chloroplasts through its N-terminal extension. In addition, our results show that <it>AtTSPO </it>is regulated at the transcriptional level in tetrapyrrole biosynthetic mutants. Thus, we propose that <it>At</it>TSPO may play a role in transporting tetrapyrrole intermediates during salt stress and other conditions in which tetrapyrrole metabolism is compromised.</p

Function and diversity of P0 proteins among cotton leafroll dwarf virus isolates

Abstract\ud \ud Background\ud The RNA silencing pathway is an important anti-viral defense mechanism in plants. As a counter defense, some members of the viral family Luteoviridae are able to evade host immunity by encoding the P0 RNA silencing suppressor protein. Here we explored the functional diversity of P0 proteins among eight cotton leafroll dwarf virus (CLRDV) isolates, a virus associated with a worldwide cotton disease known as cotton blue disease (CBD).\ud \ud \ud Methods\ud CLRDV-infected cotton plants of different varieties were collected from five growing fields in Brazil and their P0 sequences compared to three previously obtained isolates. P0’s silencing suppression activities were scored based on transient expression experiments in Nicotiana benthamiana leaves.\ud \ud \ud Results\ud High sequence diversity was observed among CLRDV P0 proteins, indicating that some isolates found in cotton varieties formerly resistant to CLRDV should be regarded as new genotypes within the species. All tested proteins were able to suppress local and systemic silencing, but with significantly variable degrees. All P0 proteins were able to mediate the decay of ARGONAUTE proteins, a key component of the RNA silencing machinery.\ud \ud \ud Conclusions\ud The sequence diversity observed in CLRDV P0s is also reflected in their silencing suppression capabilities. However, the strength of local and systemic silencing suppression was not correlated for some proteins.Instituto Matogrossense do AlgodãoConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de\ud Janeiro (FAPERJ

Glycine-rich RNA binding protein of Oryza sativa inhibits growth of M15 E. coli cells

<p>Abstract</p> <p>Background</p> <p>Plant glycine-rich RNA binding proteins have been implicated to have roles in diverse abiotic stresses.</p> <p>Findings</p> <p><it>E. coli </it>M15 cells transformed with full-length rice glycine-rich RNA binding protein4 (OsGR-RBP4), truncated rice glycine-rich RNA binding protein4 (OsGR-RBP4ΔC) and rice FK506 binding protein (OsFKBP20) were analyzed for growth profiles using both broth and solid media. Expression of OsGR-RBP4 and OsGR-RBP4ΔC proteins caused specific, inhibitory effect on growth of recombinant M15 <it>E. coli </it>cells. The bacterial inhibition was shown to be time and incubation temperature dependent. Removal of the inducer, IPTG, resulted in re-growth of the cells, indicating that effect of the foreign proteins was of reversible nature. Although noted at different levels of dilution factors, addition of purified Os-GR-RBP4 and OsGR-RBP4ΔC showed a similar inhibitory effect as seen with expression inside the bacterial cells.</p> <p>Conclusions</p> <p>Expression of eukaryotic, stress-associated OsGR-RBP4 protein in prokaryotic <it>E. coli </it>M15 cells proves injurious to the growth of the bacterial cells. <it>E. coli </it>genome does not appear to encode for any protein that has significant homology to OsGR-RBP4 protein. Therefore, the mechanism of inhibition appears to be due to some illegitimate interactions of the OsGR-RBP4 with possibly the RNA species of the trans-host bacterial cells. The detailed mechanism underlying this inhibition remains to be worked out.</p

A Glycine-Rich Protein Encoded by Sulfur-Deficiency Induced Gene Is Involved in the Regulation of Callose Level and Root Elongation

Glycine-rich proteins (GRPs) with characteristic repetitive glycine stretches are ubiquitous in organisms of all Kingdoms and have distinct functions. It is believed that Gly-rich domains serve mainly for interactions with other proteins. Previously, we identified the tobacco UP30 gene as strongly upregulated by sulfur deficiency. It encodes a protein highly similar to cdiGRP involved in tobacco defense response by elevating cell wall callose deposits thus blocking systemic movement of viruses. The closest Arabidopsis thaliana homologue of UP30 is GRP-3 (At2g05520). Here we report that GRP-3 is induced in Arabidopsis seedlings in both sulfur and nitrogen deficiency conditions. The transgenic Arabidopsis plants either overexpressing or with silenced GRP-3 expression tend to have longer roots especially in the conditions of sulfur deficiency. The effect could be reduced by the addition of auxin to the media. Moreover, we observed the increased callose deposition in both Arabidopsis lines suggesting its negative effects on shoot-to-root movement of auxins in nutrient deficient conditions

Signal transduction-related responses to phytohormones and environmental challenges in sugarcane

BACKGROUND: Sugarcane is an increasingly economically and environmentally important C4 grass, used for the production of sugar and bioethanol, a low-carbon emission fuel. Sugarcane originated from crosses of Saccharum species and is noted for its unique capacity to accumulate high amounts of sucrose in its stems. Environmental stresses limit enormously sugarcane productivity worldwide. To investigate transcriptome changes in response to environmental inputs that alter yield we used cDNA microarrays to profile expression of 1,545 genes in plants submitted to drought, phosphate starvation, herbivory and N(2)-fixing endophytic bacteria. We also investigated the response to phytohormones (abscisic acid and methyl jasmonate). The arrayed elements correspond mostly to genes involved in signal transduction, hormone biosynthesis, transcription factors, novel genes and genes corresponding to unknown proteins. RESULTS: Adopting an outliers searching method 179 genes with strikingly different expression levels were identified as differentially expressed in at least one of the treatments analysed. Self Organizing Maps were used to cluster the expression profiles of 695 genes that showed a highly correlated expression pattern among replicates. The expression data for 22 genes was evaluated for 36 experimental data points by quantitative RT-PCR indicating a validation rate of 80.5% using three biological experimental replicates. The SUCAST Database was created that provides public access to the data described in this work, linked to tissue expression profiling and the SUCAST gene category and sequence analysis. The SUCAST database also includes a categorization of the sugarcane kinome based on a phylogenetic grouping that included 182 undefined kinases. CONCLUSION: An extensive study on the sugarcane transcriptome was performed. Sugarcane genes responsive to phytohormones and to challenges sugarcane commonly deals with in the field were identified. Additionally, the protein kinases were annotated based on a phylogenetic approach. The experimental design and statistical analysis applied proved robust to unravel genes associated with a diverse array of conditions attributing novel functions to previously unknown or undefined genes. The data consolidated in the SUCAST database resource can guide further studies and be useful for the development of improved sugarcane varieties