Molecular Evolutionary Analyses of the Pseudomonas-Derived Cephalosporinase Gene.

Despite the increasing evidence of the clinical impact of Pseudomonas-derived cephalosporinase (PDC) sequence polymorphisms, the molecular evolution of its encoding gene, blaPDC, remains elusive. To elucidate this, we performed a comprehensive evolutionary analysis of blaPDC. A Bayesian Markov Chain Monte Carlo phylogenetic tree revealed that a common ancestor of blaPDC diverged approximately 4660 years ago, leading to the formation of eight clonal variants (clusters A-H). The phylogenetic distances within clusters A to G were short, whereas those within cluster H were relatively long. Two positive selection sites and many negative selection sites were estimated. Two PDC active sites overlapped with negative selection sites. In docking simulation models based on samples selected from clusters A and H, piperacillin was bound to the serine and the threonine residues of the PDC active sites, with the same binding mode for both models. These results suggest that, in P. aeruginosa, blaPDC is highly conserved, and PDC exhibits similar antibiotic resistance functionality regardless of its genotype.

Arabidopsis ENHANCER OF SHOOT REGENERATION (ESR)1 and ESR2 regulate in vitro shoot regeneration and their expressions are differentially regulated.

The Arabidopsis ENHANCER OF SHOOT REGENERATION (ESR)1 and ESR2 genes are thought to play critical roles in in vitro shoot regeneration. In this study, we investigated the functions and expression patterns of ESR1 and ESR2 during shoot regeneration by using their mutants and promoter-reporter systems. Shoot regeneration efficiencies of esr1 esr2 double mutants from hypocotyl explants decreased drastically; although the effects on shoot regeneration of the esr1 single mutation were much less marked than those of the esr2 single mutation, especially from root explants, their effects were additive. We found that ESR1 was initially expressed 1 day after transfer onto shoot-inducing medium (SIM), compared with 4 days for ESR2 expression. These results suggest that the functions of ESR1 and ESR2 in shoot regeneration are not redundant, even though they encode similar transcription factors and the ESR2 gene substituted with an ESR1 coding region complements the esr2 mutation. We also found that ESR1 expression was localized to a small number of cells in the lateral root meristem (LRM)-like structures, and the ESR1-expressing cells appeared to proliferate to form shoot apical meristem (SAM)-like structures. Thus, ESR1 may be involved in the change of LRM to SAM in tissue culture.