Novel Phakopsora pachyrhizi extracellular proteins are ideal targets for immunological diagnostic assays

Phakopsora pachyrhizi, the causal agent of Asian soybean rust (ASR), continues to spread across the southeast and midsouth regions of the United States, necessitating the use of fungicides by producers. Our objective in this research was to identify ASR proteins expressed early during infection for the development of immunodiagnostic assays. We have identified and partially characterized a small gene family encoding extracellular proteins in the P. pachyrhizi urediniospore wall, termed PHEPs (for Phakopsora extracellular protein). Two highly expressed protein family members, PHEP 107 and PHEP 369, were selected as ideal immunodiagnostic targets for antibody development, after we detected PHEPs in plants as early as 3 days postinfection (dpi). Monoclonal antibodies (MAbs; 2E8E5-1 and 3G6H7-3) generated against recombinant PHEP 369 were tested for sensitivity against the recombinant protein and extracts from ASR-infected plants and for specificity against a set of common soybean pathogens. These antibodies should prove applicable in immunodiagnostic assays to detect infected soybeans and to identify ASR spores from sentinel surveillance plots.     

The cadC gene product of alkaliphilic Bacillus firmus OF4 partially restores Na+ resistance to an Escherichia coli strain lacking an Na+/H+ antiporter (NhaA).

A 5.6-kb fragment of alkaliphilic Bacillus firmus OF4 DNA was isolated by screening a library of total genomic DNA constructed in pGEM3Zf(+) for clones that reversed the Na+ sensitivity of Escherichia coli NM81, in which the gene encoding an Na+/H+ antiporter (NhaA) is deleted (E. Padan, N. Maisler, D. Taglicht, R. Karpel, and S. Schuldiner, J. Biol. Chem. 264:20297-20302, 1989). The plasmid, designated pJB22, contained two genes that apparently encode transposition functions and two genes that are apparent homologs of the cadA and cadC genes of cadmium resistance-conferring plasmid pI258 of Staphylococcus aureus. E. coli NM81 transformed with pJB22 had enhanced membrane Na+/H+ antiporter activity that was cold labile and that decreased very rapidly following isolation of everted vesicles. Subclones of pJB22 containing cadC as the only intact gene showed identical complementation patterns in vivo and in vitro. The cadC gene product of S. aureus has been proposed to act as an accessory protein for the Cd2+ efflux ATPase (CadA) (K. P. Yoon and S. Silver, J. Bacteriol. 173:7636-7642, 1991); perhaps the alkaliphile CadC also binds Na+ and enhances antiporter activity by delivering a substrate to an integral membrane antiporter. A 6.0-kb fragment overlapping the pJB22 insert was isolated to complete the sequence of the cadA homolog. A partial sequence of a region approximately 2 kb downstream of the cadA locus shares sequence similarity with plasmids from several gram-positive bacteria. These results suggest that the region of alkaliphile DNA containing the cadCA locus is present on a transposon that could reside on a heretofore-undetected endogenous plasmid.     

The use of polyclonal antibodies to identify peptides exposed on the stroma side of the spinach thylakoid

We have raised polyclonal antibodies against an oxygen-evolving photosystem II preparation. Western Blot analysis of the whole serum revaals antibodies specific for at least 15 Coomassie visible bands ranging from 59 to 11 kDa. These antibodies are specific for proteins located on both sides of the membrane. Included are antibodies specific for Tris-removable peptides (33, 25 and 18 kda), which are thought to be exposed on the lumen surface of the PS II complex. Since the whole serum agglutinates thylakoids, antibodies specific for the stroma side of the PS II complex are also present. A sub-population of antibodies can be isolated by allowing the antibodies in whole serum to bind to EDTA-treated thylakoid membranes. The antibodies which specifically bind are cross-reactive with peptides with Mr of 59, 57, 34, 28, 27, 26, and 23 kDa. Our data indicate that these peptides have antigenic determinants exposed on the stroma side of the thylakoid membrane.     

The RNA-binding Protein TDP-43 Selectively Disrupts MicroRNA-1/206 Incorporation into the RNA-induced Silencing Complex

MicroRNA (miRNA) maturation is regulated by interaction of particular miRNA precursors with specific RNA-binding proteins. Following their biogenesis, mature miRNAs are incorporated into the RNA-induced silencing complex (RISC) where they interact with mRNAs to negatively regulate protein production. However, little is known about how mature miRNAs are regulated at the level of their activity. To address this, we screened for proteins differentially bound to the mature form of the miR-1 or miR-133 miRNA families. These muscle-enriched, co-transcribed miRNA pairs cooperate to suppress smooth muscle gene expression in the heart. However, they also have opposing roles, with the miR-1 family, composed of miR-1 and miR-206, promoting myogenic differentiation, whereas miR-133 maintains the progenitor state. Here, we describe a physical interaction between TDP-43, an RNA-binding protein that forms aggregates in the neuromuscular disease, amyotrophic lateral sclerosis, and the miR-1, but not miR-133, family. Deficiency of the TDP-43 Drosophila ortholog enhanced dmiR-1 activity in vivo. In mammalian cells, TDP-43 limited the activity of both miR-1 and miR-206, but not the miR-133 family, by disrupting their RISC association. Consistent with TDP-43 dampening miR-1/206 activity, protein levels of the miR-1/206 targets, IGF-1 and HDAC4, were elevated in TDP-43 transgenic mouse muscle. This occurred without corresponding Igf-1 or Hdac4 mRNA increases and despite higher miR-1 and miR-206 expression. Our findings reveal that TDP-43 negatively regulates the activity of the miR-1 family of miRNAs by limiting their bioavailability for RISC loading and suggest a processing-independent mechanism for differential regulation of miRNA activity.     

Identification of a Hsp70 recognition domain within the rubisco small subunit transit peptide

The interaction between SStp, the transit peptide of the precursor protein to the small subunit of Rubisco (prSSU) and two Hsp70 molecular chaperones, Escherichia coli DnaK and pea (Pisum sativum) CSS1, was investigated in detail. Two statistical analyses were developed and used to investigate and predict regions of SStp recognized by DnaK. Both algorithms suggested that DnaK would have high affinity for the N terminus of SStp, moderate affinity for the central region, and low affinity for the C terminus. Furthermore, both algorithms predicted this affinity pattern for >75% of the transit peptides analyzed in the chloroplast transit peptide (CHLPEP) database. In vitro association between SStp and these Hsp70s was confirmed by three independent assays: limited trypsin resistance, ATPase stimulation, and native gel shift. Finally, synthetic peptides scanning the length of SStp and C-terminal deletion mutants of SStp were used to experimentally map the region of greatest DnaK affinity to the N terminus. CSS1 displayed a similar affinity for the N terminus of SStp. The major stromal Hsp70s affinity for the N terminus of SStp and other transit peptides supports a molecular motor model in which the chaperone functions as an ATP-dependent translocase, committing chloroplast precursor proteins to unidirectional movement across the envelope.