Environmental cues profoundly modulate cell proliferation and cell elongation to inform and direct plant growth and development. External phosphate (Pi) limitation inhibits primary root growth in many plant species. However, the underlying Pi sensory mechanisms are unknown. Here we genetically uncouple two Pi sensing pathways in the root apex of Arabidopsis thaliana. First, the rapid inhibition of cell elongation in the transition zone is controlled by transcription factor STOP1, by its direct target, ALMT1, encoding a malate channel, and by ferroxidase LPR1, which together mediate Fe and peroxidase-dependent cell wall stiffening. Second, during the subsequent slow inhibition of cell proliferation in the apical meristem, which is mediated by LPR1-dependent, but largely STOP1–ALMT1-independent, Fe and callose accumulate in the stem cell niche, leading to meristem reduction. Our work uncovers STOP1 and ALMT1 as a signalling pathway of low Pi availability and exuded malate as an unexpected apoplastic inhibitor of root cell wall expansion.

Biological interactions underpin the functioning of marine ecosystems, be it via competition, predation, mutualism or symbiosis processes. Microbial phototroph–heterotroph interactions propel the engine that results in the biogeochemical cycling of individual elements, and they are critical for understanding and modelling global ocean processes. Unfortunately, studies thus far have focused on exponentially growing cultures in nutrient-rich media, meaning knowledge of such interactions under in situ conditions is rudimentary at best. Here, we have performed long-term phototroph–heterotroph co-culture experiments under nutrient-amended and natural seawater conditions, and show that it is not the concentration of nutrients but rather their circulation that maintains a stable interaction and a dynamic system. Using the Synechococcus–Roseobacter interaction as a model phototroph–heterotroph case study, we show that although Synechococcus is highly specialized for carrying out photosynthesis and carbon fixation, it relies on the heterotroph to remineralize the inevitably leaked organic matter, making nutrients circulate in a mutualistic system. In this sense we challenge the general belief that marine phototrophs and heterotrophs compete for the same scarce nutrients and niche space, and instead suggest that these organisms more probably benefit from each other because of their different levels of specialization and complementarity within long-term stable-state systems.

Sexual reproduction is crucially dependent on meiosis, a conserved, specialized cell division programme that is essential for the production of haploid gametes. Here we demonstrate that fertility and the implementation of the meiotic programme require a previously uncharacterized meiosis-specific protein, MEIOC.Meiocinvalidation in mice induces early and pleiotropic meiotic defects in males and females. MEIOC prevents meiotic transcript degradation and interacts with an RNA helicase that binds numerous meiotic mRNAs. Our results indicate that proper engagement into meiosis necessitates the specific stabilization of meiotic transcripts, a previously little-appreciated feature in mammals. Remarkably, the upregulation of MEIOC at the onset of meiosis does not require retinoic acid and STRA8 signalling. Thus, we propose that the complete induction of the meiotic programme requires both retinoic acid-dependent and -independent mechanisms. The latter process involving post-transcriptional regulation likely represents an ancestral mechanism, given that MEIOC homologues are conserved throughout multicellular animals.

To better understand adaptation to harsh conditions encountered in hot arid deserts, we report the first complete genome sequence and proteome analysis of a bacterium, Deinococcus deserti VCD115, isolated from Sahara surface sand. Its genome consists of a 2.8-Mb chromosome and three large plasmids of 324 kb, 314 kb, and 396 kb. Accurate primary genome annotation of its 3,455 genes was guided by extensive proteome shotgun analysis. From the large corpus of MS/MS spectra recorded, 1,348 proteins were uncovered and semiquantified by spectral counting. Among the highly detected proteins are several orphans and Deinococcus-specific proteins of unknown function. The alliance of proteomics and genomics high-throughput techniques allowed identification of 15 unpredicted genes and, surprisingly, reversal of incorrectly predicted orientation of 11 genes. Reversal of orientation of two Deinococcus-specific radiation-induced genes, ddrC and ddrH, and identification in D. deserti of supplementary genes involved in manganese import extend our knowledge of the radiotolerance toolbox of Deinococcaceae. Additional genes involved in nutrient import and in DNA repair (i.e., two extra recA, three translesion DNA polymerases, a photolyase) were also identified and found to be expressed under standard growth conditions, and, for these DNA repair genes, after exposure of the cells to UV. The supplementary nutrient import and DNA repair genes are likely important for survival and adaptation of D. deserti to its nutrient-poor, dry, and UV-exposed extreme environment. D. deserti belongs to the Deinococcaceae, a family of bacteria characterized by an exceptional ability to withstand the lethal effects of DNA-damaging agents, including ionizing radiation, UV light, and desiccation. It was isolated from Sahara surface sands, an extreme and nutrient-poor environment, regularly exposed to intense UV radiation, cycles of extreme temperatures, and desiccation. The evolution of organisms that are able to survive acute irradiation doses of 15,000 Gy is difficult to explain given the apparent absence of highly radioactive habitats on Earth over geologic time. Thus, it seems more likely that the natural selection pressure for the evolution of radiation-resistant bacteria was chronic exposure to nonradioactive forms of DNA damage, in particular those promoted by desiccation. Here, we report the first complete genome sequence of a bacterium, D. deserti VCD115, isolated from hot, arid desert surface sand. Accurate genome annotation of its 3,455 genes was guided by extensive proteome analysis in which 1,348 proteins were uncovered after growth in standard conditions. Supplementary genes involved in manganese import, in nutrient import, and in DNA repair were identified and are likely important for survival and adaptation of D. deserti to its hostile environment.