Common and specific responses to iron and phosphorus deficiencies in roots of apple tree (Malus × domestica)

Plant Molecular Biology - Iron and phosphorus are abundant elements in soils but poorly available for plant nutrition. The availability of these two nutrients represents a major constraint for...     

Food For Thought: Short-Term Fasting Upregulates Glucose Transporters in Neurons and Endothelial Cells,But Not in Astrocytes

Neurochemical Research - Our group previously reported that 6-h fasting increased both insulin II mRNA expression and insulin level in rat hypothalamus. Given that insulin effects on central...     

K2P18.1 translates T cell receptor signals into thymic regulatory T cell development

It remains largely unclear how thymocytes translate relative differences in T cell receptor (TCR) signal strength into distinct developmental programs that driv...     

Functional domains of the ubiquitous chromatin protein DEK

DEK was originally described as a proto-oncogene protein and is now known to be a major component of metazoan chromatin. DEK is able to modify the structure of DNA by introducing supercoils. In order to find interaction partners and functional domains of DEK, we performed yeast two-hybrid screens and mutational analyses. Two-hybrid screening yielded C-terminal fragments of DEK, suggesting that DEK is able to multimerize. We could localize the domain to amino acids 270 to 350 and show that multimerization is dependent on phosphorylation by CK2 kinase in vitro. We also found two DNA binding domains of DEK, one on a fragment including amino acids 87 to 187 and containing the SAF-box DNA binding motif, which is located between amino acids 149 and 187. This region is sufficient to introduce supercoils into DNA. The second DNA binding domain is located between amino acids 270 and 350 and thus overlaps the multimerization domain. We show that the two DNA-interacting domains differ in their binding properties and in their abilities to respond to CK2 phosphorylation.     

Identification of Pseudomonas syringae type III effectors that can suppress programmed cell death in plants and yeast

The Pseudomonas syringae pv. tomato DC3000 type III secretion system (TTSS) is required for bacterial pathogenicity on plants and elicitation of the hypersensitive response (HR), a programmed cell death (PCD) that occurs on resistant plants. Cosmid pHIR11 enables non-pathogens to elicit an HR dependent upon the TTSS and the effector HopPsyA. We used pHIR11 to determine that effectors HopPtoE, avirulence AvrPphEPto, AvrPpiB1Pto, AvrPtoB, and HopPtoF could suppress a HopPsyA-dependent HR on tobacco and Arabidopsis. Mixed inoculum and Agrobacterium-mediated transient expression experiments confirmed that suppressor action occurred within plant cells. These suppressors, with the exception of AvrPpiB1Pto, inhibited the expression of the tobacco pathogenesis-related (PR) gene PR1a. DC3000 suppressor mutants elicited an enhanced HR consistent with these mutants lacking an HR suppressor. Additionally, HopPtoG was identified as a suppressor on the basis of an enhanced HR produced by a hopPtoG mutant. Remarkably, these proteins functioned to inhibit the ability of the pro-apoptotic protein, Bax to induce PCD in plants and yeast, indicating that these effectors function as anti-PCD proteins in a trans-kingdom manner. The high proportion of effectors that suppress PCD suggests that suppressing plant immunity is one of the primary roles for DC3000 effectors and a central requirement for P. syringae pathogenesis.     

MprF-mediated biosynthesis of lysylphosphatidylglycerol, an important determinant in staphylococcal defensin resistance

Frequently bacteria are exposed to membrane-damaging cationic antimicrobial molecules (CAMs) produced by the host's immune system (defensins, cathelicidins) or by competing microorganisms (bacteriocins). Staphylococcus aureus achieves CAM resistance by modifying anionic phosphatidylglycerol with positively charged L-lysine, resulting in repulsion of the peptides. Inactivation of the novel S. aureus gene, mprF, which is found in many bacterial pathogens, has resulted in the loss of lysylphosphatidylglycerol (L-PG), increased inactivation by CAM-containing neutrophils, and attenuated virulence. We demonstrate here that expression of mprF is sufficient to confer L-PG production in Escherichia coli, which indicates that MprF represents the L-PG synthase. L-PG biosynthesis was studied in vitro and found to be dependent on phosphatidylglycerol and lysyl-tRNA, two putative substrate molecules. Further addition of cadaverin, a competitive inhibitor of the lysyl-tRNA synthetases, or of RNase A abolished L-PG biosynthesis, thereby confirming the involvement of lysyl-tRNA. This study forms the basis for further detailed analyses of L-PG biosynthesis and its role in bacterial infections.     

Genes coding for hepatotoxic heptapeptides (microcystins) in the cyanobacterium Anabaena strain 90

The cluster of microcystin synthetase genes from Anabaena strain 90 was sequenced and characterized. The total size of the region is 55.4 kb, and the genes are organized in three putative operons. The first operon (mcyA-mcyB-mcyC) is transcribed in the opposite direction from the second operon (mcyG-mcyD-mcyJ-mcyE-mcyF-mcyI) and the third operon (mcyH). The genes mcyA, mcyB, and mcyC encode nonribosomal peptide synthetases (NRPS), while mcyD codes for a polyketide synthase (PKS), and mcyG and mcyE are mixed NRPS-PKS genes. The genes mcyJ, mcyF, and mcyI are similar to genes coding for a methyltransferase, an aspartate racemase, and a D-3-phosphoglycerate dehydrogenase, respectively. The region in the first module of mcyB coding for the adenylation domain was found to be 96% identical with the corresponding part of mcyC, suggesting a recent duplication of this fragment and a replacement in mcyB. In Anabaena strain 90, the order of the domains encoded by the genes in the two sets (from mcyG to mcyI and from mcyA to mcyC) is colinear with the hypothetical order of the enzymatic reactions for microcystin biosynthesis. The order of the microcystin synthetase genes in Anabaena strain 90 differs from the arrangement found in two other cyanobacterial species, Microcystis aeruginosa and Planktothrix agardhii. The average sequence match between the microcystin synthetase genes of Anabaena strain 90 and the corresponding genes of the other species is 74%. The identity of the individual proteins varies from 67 to 81%. The genes of microcystin biosynthesis from three major producers of this toxin are now known. This makes it possible to design probes and primers to identify the toxin producers in the environment.