Presence of vitamin B12_{12} metabolism in the last common ancestor of land plants

International audienceVitamin B$_{12}$, or cobalamin, (hereinafter B$_{12}$) is an essential organic cofactor for methionine synthase (METH) that is only synthesised by a subset of bacteria. Plants and fungi have an alternative methionine synthase (METE) that does not need B$_{12}$, and are typically considered not to utilise it. Some algal species (e.g., Chlamydomonas) facultatively utilise B12 because they encode both METE and METH, while others are dependent on B$_{12}$ as they encode METH only. We performed phylogenomic analyses of METE, METH and eleven further B$_{12}$ metabolism proteins across over 1,600 plant and algal genomes and transcriptomes (e.g., from OneKp), demonstrating the presence of B$_{12}$-associated metabolism deep into the streptophytes. METH, and five further accessory proteins (MTRR, CblB, CblC, CblD and CblJ) were detected in the hornworts (Anthocerophyta), and two (CblB and CblJ) were identified in liverworts (Marchantiophyta) in the bryophytes, suggesting a retention of B$_{12}$-metabolism in the last common land plant ancestor. Our data further show more limited distributions for other B$_{12}$-related proteins (MCM, RNR-II), and B$_{12}$-dependency in several algal orders. Finally, considering the collection sites of algae that have lost B$_{12}$ metabolism, we propose freshwater-to-land transitions and symbiotic associations to have been constraining factors for B$_{12}$ availability in early plant evolution

A stalagmite test of North Atlantic SST and Iberian hydroclimate linkages over the last two glacial cycles

Close coupling of Iberian hydroclimate and North Atlantic sea surface temperature (SST) during recent glacial periods has been identified through the analysis of marine sediment and pollen grains co-deposited on the Portuguese continental margin. While offering precisely correlatable records, these time series have lacked a directly dated, site-specific record of continental Iberian climate spanning multiple glacial cycles as a point of comparison. Here we present a high-resolution, multi-proxy (growth dynamics and δ13C, δ18O, and δ234U values) composite stalagmite record of hydroclimate from two caves in western Portugal across the majority of the last two glacial cycles (∼220 ka). At orbital and millennial scales, stalagmite-based proxies for hydroclimate proxies covaried with SST, with elevated δ13C, δ18O, and δ234Uvalues and/or growth hiatuses indicating reduced effective moisture coincident with periods of lowered SST during major ice-rafted debris events, in agreement with changes in palynological reconstructions of continental climate. While in many cases the Portuguese stalagmite record can be scaled to SST, in some intervals the magnitudes of stalagmite isotopic shifts, and possibly hydroclimate, appear to have been somewhat decoupled from SST.This article is published as Denniston, R. F., Houts, A. N., Asmerom, Y., Wanamaker Jr., A. D., Haws, J. A., Polyak, V. J., Thatcher, D. L., Altan-Ochir, S., Borowske, A. C., Breitenbach, S. F. M., Ummenhofer, C. C., Regala, F. T., Benedetti, M. M., and Bicho, N. F.: A stalagmite test of North Atlantic SST and Iberian hydroclimate linkages over the last two glacial cycles, Clim. Past, 14 (2018): 1893-1913, doi: 10.5194/cp-14-1893-2018.</p