Globally, reef-building corals are the most prolific producers of dimethylsulphoniopropionate (DMSP) 1,2 , a central molecule in the marine sulphur cycle and precursor of the climate-active gas dimethylsulphide 3,4 . At present, DMSP production by corals is attributed entirely to their algal endosymbiont, Symbiodinium 2 . Combining chemical, genomic and molecular approaches, we show that coral juveniles produce DMSP in the absence of algal symbionts. DMSP levels increased up to 54% over time in newly settled coral juveniles lacking algal endosymbionts, and further increases, up to 76%, were recorded when juveniles were subjected to thermal stress. We uncovered coral orthologues of two algal genes recently identified in DMSP biosynthesis, strongly indicating that corals possess the enzymatic machinery necessary for DMSP production. Our results overturn the paradigm that photosynthetic organisms are the sole biological source of DMSP, and highlight the double jeopardy represented by worldwide declining coral cover, as the potential to alleviate thermal stress through coral-produced DMSP declines correspondingly.It is widely accepted that the production of dimethylsulphoniopropionate (DMSP), a central molecule in the marine sulphur cycle, is restricted to marine algae and a few species of intertidal plants 5. Marine bacteria subsequently use DMSP as a source of sulphur and carbon and can metabolize this compound into the volatile gas dimethylsulphide (DMS) 6 , by which the largest natural flux of sulphur enters the atmosphere where it exerts considerable influence on atmospheric chemistry 7 . Despite recent controversy regarding the impact of DMS emissions on global climate 8 , DMS is probably involved in local climate regulation through its oxidation into aerosol particles that induce the formation of clouds and increase their reflectivity, thereby reducing light levels and water temperatures in the marine environment 3,4 . Concentrations of DMSP and DMS found in reef-building corals are among the highest recorded in the environment 1,2 , but it has been assumed that DMSP production derives solely from the coral's endosymbiotic microalgae Symbiodinium. Evidence that the total amounts of DMSP recorded in corals are consistently higher than levels present in Symbiodinium cells alone 9,10 raises the possibility of a cryptic source of DMSP in reef-building corals. A clear understanding of the sources of DMSP on reefs and the possible effects that global warming may have on DMSP production is paramount, given the influence that coralreef-derived sulphur emissions may have on local climates 11 . Corals in the genus Acropora are the most abundant reef-building organisms in the Indo-Pacific region 12 and, as broadcast spawners, they acquire Symbiodinium from their surrounding environment after larval development. The Symbiodinium-free larvae of this genus provide a unique opportunity to investigate Symbiodinium-independent production of DMSP in corals. Results presented here demonstrate that coral hosts (kingdom: Ani...

Plants rapidly release photoassimilated carbon (C) to the soil via direct root exudation and associated mycorrhizal fungi, with both pathways promoting plant nutrient availability. This study aimed to explore these pathways from the root's vascular bundle to soil microbial communities.Using nanoscale secondary ion mass spectrometry (NanoSIMS) imaging and 13C-phospho- and neutral lipid fatty acids, we traced in-situ flows of recently photoassimilated C of 13CO2-exposed wheat (Triticum aestivum) through arbuscular mycorrhiza (AM) into root- and hyphae-associated soil microbial communities.Intraradical hyphae of AM fungi were significantly 13C-enriched compared to other root-cortex areas after 8 h of labelling. Immature fine root areas close to the root tip, where AM features were absent, showed signs of passive C loss and co-location of photoassimilates with nitrogen taken up from the soil solution. A significant and exclusively fresh proportion of 13C-photosynthates was delivered through the AM pathway and was utilised by different microbial groups compared to C directly released by roots.Our results indicate that a major release of recent photosynthates into soil leave plant roots via AM intraradical hyphae already upstream of passive root exudations. AM fungi may act as a rapid hub for translocating fresh plant C to soil microbes.

Dimethylsulfoniopropionate (DMSP) is a globally important organosulfur molecule and the major precursor for dimethyl sulfide. These compounds are important info-chemicals, key nutrients for marine microorganisms, and are involved in global sulfur cycling, atmospheric chemistry and cloud formation. DMSP production was thought to be confined to eukaryotes, but heterotrophic bacteria can also produce DMSP through the pathway used by most phytoplankton , and the DsyB enzyme catalysing the key step of this pathway in bacteria was recently identified . However, eukaryotic phytoplankton probably produce most of Earth's DMSP, yet no DMSP biosynthesis genes have been identified in any such organisms. Here we identify functional dsyB homologues, termed DSYB, in many phytoplankton and corals. DSYB is a methylthiohydroxybutryate methyltransferase enzyme localized in the chloroplasts and mitochondria of the haptophyte Prymnesium parvum, and stable isotope tracking experiments support these organelles as sites of DMSP synthesis. DSYB transcription levels increased with DMSP concentrations in different phytoplankton and were indicative of intracellular DMSP. Identification of the eukaryotic DSYB sequences, along with bacterial dsyB, provides the first molecular tools to predict the relative contributions of eukaryotes and prokaryotes to global DMSP production. Furthermore, evolutionary analysis suggests that eukaryotic DSYB originated in bacteria and was passed to eukaryotes early in their evolution.

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