PubMed · 6160952
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P R Schimmel. 1980. Five specific protein-transfer RNA interactions.. https://doi.org/10.3109/10409238009105435
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Chalcone synthase (CHS) is a pivotal enzyme in flavonoid biosynthesis involved in plant development, defense, and secondary metabolism. Xanthoceras sorbifolium (yellowhorn) is a medicinal and ornamental species with high resistance to environmental stresses, but its CHS gene family remains uncharacterized. We performed a pangenome-wide identification of CHS genes across five yellowhorn genomes (Xzs4, Xwf8, Xjg, Xg11, and Xzg2). Across the five yellowhorn genomes, 27 CHS genes were identified and classified into four core pangenes, present in all five genomes, and two dispensable genes, present only in a subset of genomes. Phylogenetic analysis grouped these genes into three major clades, and chromosomal mapping and duplication analyses identified four tandemly duplicated gene pairs under purifying selection. The analyses of conserved structural features, including protein motifs and exon-intron organization, together with promoter cis-regulatory elements and gene ontology annotation, further indicated the potential involvement of CHS genes in flavonoid biosynthesis and stress-responsive mechanisms. Gene expression profiling identified significant upregulation of Xg11_CHS1 and Xg11_CHS3 under cold and drought stress, with tissue-specific expression patterns. These findings provide valuable insights into the evolution, functional diversification, and stress-responsive roles of the CHS gene family, identifying candidate genes for future studies targeting stress tolerance and flavonoid biosynthesis in yellowhorn.
By in vitro and in vivo studies with Escherichia coli expressing different combinations of the nodABCS genes of Azorhizobium caulinodans, Nod factor intermediates were identified and their structures determined using mass spectrometry. Substrate-product relationships were studied by time course experiments, and the Nod factor biosynthetic pathway was partially resolved. E. coli strains, harboring nodA and/or nodB, did not produce Nod metabolites, whereas the strain expressing nodC produced chitooligosaccharides. Thus, the first committed step was the production of the carbohydrate backbone. Bacitracin and tunicamycin did not affect this step, suggesting that undecaprenyl pyrophosphate-linked intermediates were not involved. The second step was the deacetylation of chitooligosaccharides by NodB since the E. coli strain expressing nodBC produced chitooligosaccharides, deacetylated at the non-reducing end and since the NodC products were precursors of the NodBC products. A strain expressing nodBCS produced N-methylated oligosaccharides, whereas a strain expressing nodCS produced unmethylated oligosaccharides. Time course experiments showed that methylation occurred after deacetylation. Thus, NodS acted after NodB. The NodBCS metabolites were partially converted to lipo-chitooligosaccharides when the nodABCS genes were expressed, showing that NodA was involved in the acylation and acted after NodS.
Reversible enzyme inhibition by phenylarsenoxides is generally taken to indicate the presence of functionally important vicinal thiol groups. Arginyl aminoacyl-tRNA transferase from eukaryotes is potently inhibited by phenylarsenoxides and possesses one or more essential sulfhydryl groups (Li, J., & Pickart C. M. (1995) Biochemistry 34, 139-147]. To map the putative Cys residues that mediate arsenoxide binding to the transferase from Saccharomyces cerevisiae, we systematically mutagenized the 15 Cys residues of the transferase, singly and in combination, to Ala (13 Cys) or Ser (2 Cys). Six mutant enzymes, encompassing all 15 Cys residues of the transferase, were characterized in detail. The results revealed that Cys-20, Cys-23, and Cys-94 and/or Cys-95 were important for activity, since mutations at these positions reduced activity by 100-fold (Cys-94 and Cys-95 were mutated simultaneously). Surprisingly, however, all of the mutant enzymes retained the ability to bind a radioiodinated phenylarsenoxide derivative, with undiminished stoichiometry and affinity. All of the mutant enzymes also remained susceptible to irreversible reaction with a bifunctional phenylarsenoxide bearing a paraalkyl halide substituent. Prior reaction of the enzyme with the bifunctional reagent blocked subsequent binding of the radiolabeled phenylarsenoxide, indicating that these two reagents bind at a single common site. These results indicate that high-affinity binding of trivalent arsenicals can occur by a thiol-independent mechanism.