Genome sequencing and population genomic analyses provide insights into the adaptive landscape of silver birch.

Silver birch (Betula pendula) is a pioneer boreal tree that can be induced to flower within 1 year. Its rapid life cycle, small (440-Mb) genome, and advanced germplasm resources make birch an attractive model for forest biotechnology. We assembled and chromosomally anchored the nuclear genome of an inbred B. pendula individual. Gene duplicates from the paleohexaploid event were enriched for transcriptional regulation, whereas tandem duplicates were overrepresented by environmental responses. Population resequencing of 80 individuals showed effective population size crashes at major points of climatic upheaval. Selective sweeps were enriched among polyploid duplicates encoding key developmental and physiological triggering functions, suggesting that local adaptation has tuned the timing of and cross-talk between fundamental plant processes. Variation around the tightly-linked light response genes PHYC and FRS10 correlated with latitude and longitude and temperature, and with precipitation for PHYC. Similar associations characterized the growth-promoting cytokinin response regulator ARR1, and the wood development genes KAK and MED5A

Expression of Two Novel β-Glucosidases from Chaetomium atrobrunneum in Trichoderma reesei and Characterization of the Heterologous Protein Products

Two novel GH3 family thermostable β-glucosidases from the filamentous fungus Chaetomium atrobrunneum (CEL3a and CEL3b) were expressed in Trichoderma reesei, purified by two-step ion exchange chromatography, and characterized. Both enzymes were active over a wide range of pH as compared to Neurospora crassa β-glucosidase GH3-3, which was also expressed in T. reesei and purified. The optimum temperature of both C. atrobrunneum enzymes was around 60 °C at pH 5, and both enzymes had better thermal and pH stability and higher resistance to metallic compounds and to glucose inhibition than GH3-3. They also showed higher activity against oligosaccharides composed of glucose units and linked with β-1,4-glycosidic bonds and moreover, had higher affinity for cellotriose over cellobiose. In hydrolysis tests against Avicel cellulose and steam-exploded sugarcane bagasse, performed at 45 °C, particularly the CEL3a enzyme performed similarly to N. crassa GH3-3 β-glucosidase. Taking into account the thermal stability of the C. atrobrunneum β-glucosidases, they both represent promising alternatives as enzyme mixture components for improved cellulose saccharification at elevated temperatures