LIN, a novel type of U-box/WD40 protein, controls early infection by rhizobia in legumes

The formation of a nitrogen-fixing nodule requires the coordinated development of rhizobial colonization and nodule organogenesis. Based on its mutant phenotype, lumpy infections (lin), LIN functions at an early stage of the rhizobial symbiotic process, required for both infection thread growth in root hair cells and the further development of nodule primordia. We show that spontaneous nodulation activated by the calcium- and calmodulin-dependent protein kinase is independent of LIN; thus, LIN is not necessary for nodule organogenesis. From this, we infer that LIN predominantly functions during rhizobial colonization and that the abortion of this process in lin mutants leads to a suppression of nodule development. Here, we identify the LIN gene in Medicago truncatula and Lotus japonicus, showing that it codes for a predicted E3 ubiquitin ligase containing a highly conserved U-box and WD40 repeat domains. Ubiquitin-mediated protein degradation is a universal mechanism to regulate many biological processes by eliminating rate-limiting enzymes and key components such as transcription factors. We propose that LIN is a regulator of the component(s) of the nodulation factor signal transduction pathway and that its function is required for correct temporal and spatial activity of the target protein(s).

Inhibition of bacterial plasmid replication by stereoselective binding by tricyclic psychopharmacons

Several dibenzazepines, thioxanthene, and phenothiazine stereoisomers were studied for their abilities to inhibit plasmid replication, intracellular transfer of R-plasmid, bacterial ATP-ase, and mouse serum cholinesterase isoenzyme. Partially saturated derivative of desipramine inhibited plasmid replication and transfer, but the fully saturated derivative was inactive. The inhibition of plasmid curing and transfer patterns did not correlate with the inhibition of ATP-ase and cholinesterase. Trans-clopenthixol was more effective in plasmid elimination than the cis-isomer. On the other hand, the cis-isomer inhibited ATP-ase and cholinesterase more than the trans-isomer. The levo- and dextro-methoxytrimeprazine also inhibited plasmid replication and enzyme activity. We believe that the tricyclic configuration of the drugs tested for stereospecific binding to bacterial receptors is more important than its side chain orientation. We believe that there is a similarity between bacterial receptor sites and neural receptor sites. Therefore, this model may be useful in the study of neuropharmacological agents as potential antibacterial agents.