Enzymatic cleavage of dimethylsulfoniopropionate (DMSP) in cell-free extracts of the marine macroalga Enteromorpha clathrata (Roth) Grev. (Ulvales, Chlorophyta)

The enzymatic cleavage of dimethylsulfoniopropionate (DMSP) to dimethylsulfide (DMS) in the marine macroalga Enteromorpha clathrata (Roth) Grey. (Ulvales, Chlorophyta) showed a maximum activity of 3.1 μmol DMS min-1 (mg protein)-1 at 25°C and a pH optimum of 6.2 to 6.4. The activity was more sensitive to temperature than to pH changes. With ammonium sulfate precipitation, approximately 90% of the activity was found in the 0-35% fraction, indicating a fairly hydrophobic enzyme. Activity was increased by addition of detergents during extraction. These results suggest that the DMSP lyase enzyme is probably membrane-bound in vivo. The enzyme activity is relatively insensitive to chloride salt concentrations. Addition of nucleosides and nucleotides did not increase enzyme activity. After hyperosmotic shock for 72 h, enzyme activity increased 1.7-fold and intracellular DMSP concentration was enhanced from initially 80 mmol DMSP (kg freshweight)-1 to 107 mmol DMSP (kg freshweight)-1. The results suggest that DMSP cleavage within the cell by algal DMSP lyase may contribute to the production of oceanic and atmospheric DMS

The genome of black cottonwood, Populus trichocarpa (Torr. & Gray)

We report the draft genome of the black cottonwood tree, Populus trichocarpa. Integration of shotgun sequence assembly with genetic mapping enabled chromosome-scale reconstruction of the genome. More than 45,000 putative protein-coding genes were identified. Analysis of the assembled genome revealed a whole-genome duplication event; about 8000 pairs of duplicated genes from that event survived in the Populus genome. A second, older duplication event is indistinguishably coincident with the divergence of the Populus and Arabidopsis lineages. Nucleotide substitution, tandem gene duplication, and gross chromosomal rearrangement appear to proceed substantially more slowly in Populus than in Arabidopsis. Populus has more protein-coding genes than Arabidopsis, ranging on average from 1.4 to 1.6 putative Populus homologs for each Arabidopsis gene. However, the relative frequency of protein domains in the two genomes is similar. Overrepresented exceptions in Populus include genes associated with lignocellulosic wall biosynthesis, meristem development, disease resistance, and metabolite transport