Proton gradient mediates hemolymph trehalose influx into aphid bacteriocytes.

Aphids harbor proteobacterial endosymbionts such as Buchnera aphidicola housed in specialized bacteriocytes derived from host cells. The endosymbiont Buchnera supplies essential amino acids such as arginine to the host cells and, in turn, obtains sugars needed for its survival from the hemolymph. The mechanism of sugar supply in aphid bacteriocytes has been rarely studied. It also remains unclear how Buchnera acquires its carbon source. The hemolymph sugars in Acyrthosiphon pisum are composed of the disaccharide trehalose containing two glucose molecules. Here, we report for the first time that trehalose is transported and used as a potential carbon source by Buchnera across the bacteriocyte plasma membrane via trehalose transporters. The current study characterized the bacteriocyte trehalose transporter Ap_ST11 (LOC100159441) using the Xenopus oocyte expression system. The Ap_ST11 transporter was found to be proton-dependent with a Km value ≥700 mM. We re-examined the hemolymph trehalose at 217.8 mM using a fluorescent trehalose sensor. The bacteriocytes did not obtain trehalose by facilitated diffusion along the gradient across cellular membranes. These findings suggest that trehalose influx into the bacteriocytes depends on the extracellular proton-driven secondary electrochemical transporter.

Omics analyses and biochemical study of Phlebiopsis gigantea elucidate its degradation strategy of wood extractives.

Wood extractives, solvent-soluble fractions of woody biomass, are considered to be a factor impeding or excluding fungal colonization on the freshly harvested conifers. Among wood decay fungi, the basidiomycete Phlebiopsis gigantea has evolved a unique enzyme system to efficiently transform or degrade conifer extractives but little is known about the mechanism(s). In this study, to clarify the mechanism(s) of softwood degradation, we examined the transcriptome, proteome, and metabolome of P. gigantea when grown on defined media containing microcrystalline cellulose and pine sapwood extractives. Beyond the conventional enzymes often associated with cellulose, hemicellulose and lignin degradation, an array of enzymes implicated in the metabolism of softwood lipophilic extractives such as fatty and resin acids, steroids and glycerides was significantly up-regulated. Among these, a highly expressed and inducible lipase is likely responsible for lipophilic extractive degradation, based on its extracellular location and our characterization of the recombinant enzyme. Our results provide insight into physiological roles of extractives in the interaction between wood and fungi.