Regulation of catalytic activity of a multifunctional polyketide biosynthetic enzyme, 6-hydroxymellein synthase, by interaction between NADPH and phenylglyoxal-sensitive amino acid residue at the reaction center

Treatment of 6-hydroxymellein synthase, a multifunctional polyketide biosynthetic enzyme in carrot cells, with phenylglyoxal yielded a chemically modified protein in which approximately two moles of the reagent were covalently attached to each subunit of the enzyme. Only NADH- but not NADPH-associated form of native 6-hydroxymellein synthase was inhibited by cerulenin; however, the NADPH-synthase complex lost the insensitivity by the chemical modification of the enzyme protein with phenylglyoxal. Appreciable differences in K(m) values observed between the NADPH- and NADH-associated enzymes were greatly reduced by the treatment with phenylglyoxal. Although the catalytic activity of the NADPH-associated synthase was enhanced by the addition of free CoA, the compound exhibited a significant inhibitory activity to the phenylglyoxal-modified enzyme. A marked deuterium isotope effect in the catalytic reaction of the native synthase-NADPH complex was appreciably decreased in the chemically modified enzyme. These results strongly suggest that an electrostatic interaction between the phosphate group attached to the 2'-position of adenosyl moiety of NADPH and the phenylglyoxal-sensitive amino acid residue, probably arginine, at the reaction center of 6-hydroxymellein synthase regulates several biochemical properties of this multifunctional enzyme.     

Global photosynthetic capacity is optimized to the environment

Earth system models (ESMs) use photosynthetic capacity, indexed by the maximum Rubisco carboxylation rate (V_cmax), to simulate carbon assimilation and typically rely on empirical estimates, including an assumed dependence on leaf nitrogen determined from soil fertility. In contrast, new theory, based on biochemical coordination and co‐optimization of carboxylation and water costs for photosynthesis, suggests that optimal V_cmax can be predicted from climate alone, irrespective of soil fertility. Here, we develop this theory and find it captures 64% of observed variability in a global, field‐measured V_cmax dataset for C₃ plants. Soil fertility indices explained substantially less variation (32%). These results indicate that environmentally regulated biophysical constraints and light availability are the first‐order drivers of global photosynthetic capacity. Through acclimation and adaptation, plants efficiently utilize resources at the leaf level, thus maximizing potential resource use for growth and reproduction. Our theory offers a robust strategy for dynamically predicting photosynthetic capacity in ESMs.     

Ecophysiology of Thioploca ingrica as revealed by the complete genome sequence supplemented with proteomic evidence

Large sulfur-oxidizing bacteria, which accumulate a high concentration of nitrate, are important constituents of aquatic sediment ecosystems. No representative of this group has been isolated in pure culture, and only fragmented draft genome sequences are available for these microorganisms. In this study, we successfully reconstituted the genome of Thioploca ingrica from metagenomic sequences, thereby generating the first complete genome sequence from this group. The Thioploca samples for the metagenomic analysis were obtained from a freshwater lake in Japan. A PCR-free paired-end library was constructed from the DNA extracted from the samples and was sequenced on the Illumina MiSeq platform. By closing gaps within and between the scaffolds, we obtained a circular chromosome and a plasmid-like element. The reconstituted chromosome was 4.8 Mbp in length with a 41.2% GC content. A sulfur oxidation pathway identical to that suggested for the closest relatives of Thioploca was deduced from the reconstituted genome. A full set of genes required for respiratory nitrate reduction to dinitrogen gas was also identified. We further performed a proteomic analysis of the Thioploca sample and detected many enzymes/proteins involved in sulfur oxidation, nitrate respiration and inorganic carbon fixation as major components of the protein extracts from the sample, suggesting that these metabolic activities are strongly associated with the physiology of T. ingrica in lake sediment.     

Evolutionary change in a pine wilt system following the invasion of Japan by the pinewood nematode, <Emphasis Type="Italic">Bursaphelenchus</Emphasis><Emphasis Type="Italic">xylophilus</Emphasis>

Pinewood nematode (PWN), Bursaphelenchus xylophilus, is the causative agent of pine wilt disease (PWD) of pine trees and is transmitted by cerambycid beetles belonging to the genus Monochamus. PWN is believed to have been introduced into Japan from North America at the beginning of the 20th century. In this article, we first provide an outline of the PWD system and the range expansion of PWN in Japan and then review the literature, focusing on the virulence of PWN. Virulence is a heritable trait in PWN, with high virulence being closely related to a high rate of reproduction and within-tree dispersal. When two PWN isolates with different virulence levels are inoculated into pine seedlings, the more virulent nematodes always dominate in dead seedlings. In a laboratory setting, many more virulent nematodes board the insect vectors than avirulent ones. The age at which vectors transmit the most abundant PWNs to pine twigs changes during the course of a PWD epidemic. However, the relation between virulence and transmission of PWN remains as yet relatively unknown. Such information would enable ecologists to predict the evolution of the PWD system. In this review we also compare ecological traits between the PWN and the avirulent congener, B. mucronatus.