The sll0886 gene, controlling light-activated heterotrophic growth, is involved in regulating phototaxis in cyanobacterium Synechocystis sp. PCC 6893

The sll0886 gene, controlling light-activated heterotrophic growth (LAHG), was tested for the role in regulating phototaxis in cyanobacterium Synechocystis sp. PCC 6803. Insertional inactivation of the gene in the genome of a wildtype strain did not affect positive (toward light) or negative (away from high light) phototaxis. However, cells lost motility when sll0886 inactivation was combined with the prqRL17Q mutation, which determined negative phototaxis at low light. Immotile cells with the prqRL17Q mutation and the inactivated sll0886 gene did not display any defect in the formation of type IV pili, essential for phototaxis. Hence, the function, rather than biogenesis, of pili was affected. It was concluded that the sll0886 gene, coding for a TPR family protein, is involved in controlling negative phototaxis of cyanobacteria at the level of photoreception and signal transduction and that its role is mediated by the unidentified redundant gene whose function is suppressed by the prqRL17Q mutation.     

Intranuclear localization of iron in neurons of mammalian brain

Using Perls’ histochemical method, iron was revealed in the brain structures of human and rat. Iron accumulation was observed in perivascular areas and neuropil of substantia nigra as well as in white matter of cerebellum. After diaminobenzidine enhancement of histochemical reaction, the iron was revealed in nucleoli of many neurons, which is described for the first time in animal cells.     

A conserved carboxylesterase is a SUPPRESSOR OF AVRBST-ELICITED RESISTANCE in Arabidopsis

AvrBsT is a type III effector from Xanthomonas campestris pv vesicatoria that is translocated into plant cells during infection. AvrBsT is predicted to encode a Cys protease that targets intracellular host proteins. To dissect AvrBsT function and recognition in Arabidopsis thaliana, 71 ecotypes were screened to identify lines that elicit an AvrBsT-dependent hypersensitive response (HR) after Xanthomonas campestris pv campestris (Xcc) infection. The HR was observed only in the Pi-0 ecotype infected with Xcc strain 8004 expressing AvrBsT. To create a robust pathosystem to study AvrBsT immunity in Arabidopsis, the foliar pathogen Pseudomonas syringae pv tomato (Pst) strain DC3000 was engineered to translocate AvrBsT into Arabidopsis by the Pseudomonas type III secretion (T3S) system. Pi-0 leaves infected with Pst DC3000 expressing a Pst T3S signal fused to AvrBsT-HA (AvrBsTHYB-HA) elicited HR and limited pathogen growth, confirming that the HR leads to defense. Resistance in Pi-0 is caused by a recessive mutation predicted to inactivate a carboxylesterase known to hydrolyze lysophospholipids and acylated proteins in eukaryotes. Transgenic Pi-0 plants expressing the wild-type Columbia allele are susceptible to Pst DC3000 AvrBsTHYB-HA infection. Furthermore, wild-type recombinant protein cleaves synthetic p-nitrophenyl ester substrates in vitro. These data indicate that the carboxylesterase inhibits AvrBsT-triggered phenotypes in Arabidopsis. Here, we present the cloning and characterization of the SUPPRESSOR OF AVRBST-ELICITED RESISTANCE1.     

Functional analysis of the tubulin-folding cofactor C in Arabidopsis thaliana

The biogenesis of microtubules comprises several steps, including the correct folding of alpha- and beta-tubulin and heterodimer formation. In vitro studies and the genetic analysis in yeast revealed that, after translation, alpha- and beta-tubulin are processed by several chaperonins and microtubule-folding cofactors (TFCs) to produce assembly-competent alpha-/beta-tubulin heterodimers. One of the TFCs, TFC-C, does not exist in yeast, and a potential function of TFC-C is thus based only on the biochemical analysis. In this study and in a very recently published study by Steinborn and coworkers, the analysis of the Arabidopsis porcino (por) mutant has shown that TFC-C is important for microtubule function in vivo. The predicted POR protein shares weak amino acid similarity with the human TFC-C (hTFC-C). Our finding that hTFC-C under the control of the ubiquitously expressed 35S promoter can rescue the por mutant phenotype shows that the POR gene encodes the Arabidopsis ortholog of hTFC-C. The analysis of plants carrying a GFP:POR fusion construct showed that POR protein is localized in the cytoplasm and is not associated with microtubules. While, in por mutants, microtubule density was indistinguishable from wild-type, their organization was affected.