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How parental histone (H3-H4)2 tetramers, the primary carriers of epigenetic modifications, are transferred onto leading and lagging strands of DNA replication forks for epigenetic inheritance remains elusive. Here we show that parental (H3-H4)2 tetramers are assembled into nucleosomes onto both leading and lagging strands, with a slight preference for lagging strands. The lagging strand preference increases markedly in cells lacking Dpb3 and Dpb4, two subunits of the leading strand DNA polymerase, Pol ε, due to the impairment of parental (H3-H4)2 transfer to leading strands. Dpb3-Dpb4 binds H3-H4 in vitro and participates in the inheritance of heterochromatin. These results indicate that different proteins facilitate the transfer of parental (H3-H4)2 onto leading vs lagging strands, and that Dbp3-Dpb4 plays a significant role in this poorly understood process., Special Issue: SI

Metal ions are essential elements for all living organisms. However, metals can be toxic when present in excess. In plants, metal homeostasis is partly achieved through the function of metal transporters, including the diverse natural resistance-associated macrophage proteins (NRAMP). Among them, the OsNramp6 gene encodes a previously uncharacterized member of the rice NRAMP family that undergoes alternative splicing to produce different NRAMP6 proteins. In this work, we determined the metal transport activity and biological role of the full-length and the shortest NRAMP6 proteins (l-NRAMP6 and s-NRAMP6, respectively). Both l-NRAMP6 and s-NRAMP6 are plasma membrane-localized proteins that function as iron and manganese transporters. The expression of l-Nramp6 and s-Nramp6 is regulated during infection with the fungal pathogen Magnaporthe oryzae, albeit with different kinetics. Rice plants grown under high iron supply show stronger induction of rice defense genes and enhanced resistance to M. oryzae infection. Also, loss of function of OsNramp6 results in enhanced resistance to M. oryzae, supporting the idea that OsNramp6 negatively regulates rice immunity. Furthermore, nramp6 plants showed reduced biomass, pointing to a role of OsNramp6 in plant growth. A better understanding of OsNramp6-mediated mechanisms underlying disease resistance in rice will help in developing appropriate strategies for crop protection.

[EN] Regulated expression of the Ena1 Na+-ATPase is a crucial event for adaptation to high salt and/or alkaline pH stress in the budding yeast Saccharomyces cerevisiae. ENA1 expression is under the control of diverse signaling pathways, including that mediated by the calcium-regulatable protein phosphatase calcineurin and its downstream transcription factor Crz1. We present here a quantitative study of the expression of Ena1 in response to alkalinization of the environment and we analyze the contribution of Crz1 to this response. Experimental data and mathematical models substantiate the existence of two stress-responsive Crz1-binding sites in the ENA1 promoter and estimate that the contribution of Crz1 to the early response of the ENA1 promoter is about 60%. The models suggest the existence of a second input with similar kinetics, which would be likely mediated by high pH-induced activation of the Snf1 kinase.

[EN] Regulated expression of the Ena1 Na+-ATPase is a crucial event for adaptation to high salt and/or alkaline pH stress in the budding yeast Saccharomyces cerevisiae. ENA1 expression is under the control of diverse signaling pathways, including that mediated by the calcium-regulatable protein phosphatase calcineurin and its downstream transcription factor Crz1. We present here a quantitative study of the expression of Ena1 in response to alkalinization of the environment and we analyze the contribution of Crz1 to this response. Experimental data and mathematical models substantiate the existence of two stress-responsive Crz1-binding sites in the ENA1 promoter and estimate that the contribution of Crz1 to the early response of the ENA1 promoter is about 60%. The models suggest the existence of a second input with similar kinetics, which would be likely mediated by high pH-induced activation of the Snf1 kinase.

Els microorganismes estan exposats a canvis en l'ambient que poden implicar una situació d'estrès. El llevat Saccharomyces cerevisiae prefereix condicions acides per proliferar; per tant, l'alcalinització del medi extern li empitjora el creixement. Per superar aquest estrès, el llevat activa diverses vies de senyalització que conformen una complexa xarxa reguladora, provocant un remodelament transcripcional. La via de la calcineurina, activada per l'increment de calci citosòlic en condicions alcalines, governa l'expressió gènica a través del factor de transcripció Crz1. Un estrès alcalí és detectat per la proteïna transmembrana Rim21, un component de la via Rim101, que desencadena una cascada de senyalització provocant l'activació per proteòlisi de Rim101. Aquest factor de transcripció reprimeix l'expressió de NRG1, un altre repressor transcripcional, induint així l'expressió de determinats gens indirectament. La quinasa Snf1 també s'activa per estrès alcalí i té varies dianes a través de les quals controla diferents processos. Entre aquestes, Snf1 inhibeix els repressors Mig1/Mig2 i Nrg1/Nrg2, alleugerint la repressió d'un grup divers de gens. Addicionalment, un increment del pH extern activa la via de senyalització PHO, relacionada amb l'escassetat de fosfat, provocant la inactivació del complex Pho80-Pho85 i la subseqüent acumulació de Pho4 al nucli. Aquest factor de transcripció, conjuntament amb Pho2, és responsable de l'expressió del reguló PHO, la funció del qual és mantenir els nivells de fosfat intracel·lular. El gen ENA1, que codifica una Na+-ATPasa, és un clar exemple de coregulació per diferents vies de senyalització. La seva inducció alcalina depèn de Crz1 i de l'alliberament de la repressió de Nrg1, Mig i Mig2, els quals son inhibits per Rim101 i Snf1. Pho89 és un cotransportador de sodi/fosfat d'alta afinitat membre del reguló PHO. Apart de ser induït per Pho4, sota condicions alcalines l'expressió de PHO89 també depèn de Crz1, sent l'únic gen del reg, Microorganisms are exposed to slight changes in the environment, which may imply a stressful situation. The budding yeast Saccharomyces cerevisiae prefers acidic conditions to proliferate; hence, an alkalinization of the external medium impairs its growth. To cope with this stress, S. cerevisiae activates several signaling pathways that create a complex regulatory network, leading to a profound remodeling of the transcriptional profile. The calcineurin pathway, activated by an increase of cytosolic calcium occurring in alkaline conditions, governs gene expression through the transcription factor Crz1. Moreover, high pH stress is sensed by the transmembrane protein Rim21, a component of the Rim101 pathway, which starts a signaling cascade resulting in the proteolytic activation of Rim101. This transcription factor represses the expression of NRG1, another transcriptional repressor, thus indirectly inducing the expression of certain genes. The Snf1 kinase is also activated by alkaline stress and has several targets through which it controls different processes. Among them, Snf1 inhibits the repressors Mig1/Mig2 and Nrg1/Nrg2, alleviating the repression of a diverse group of genes. Furthermore, an increase of the external pH also triggers the PHO signaling pathway, related to phosphate scarcity, causing the inactivation of the Pho80-Pho85 complex and the subsequent accumulation of Pho4 into the nucleus. This transcription factor, along with Pho2, is responsible for the expression of the PHO regulon, the function of which is to maintain the intracellular phosphate pool. The Na+-ATPase-encoding gene ENA1 is an excellent example of coregulation by different signaling pathways. The alkaline induction of this gene depends on Crz1 and on release from the repression by Nrg1, Mig1, and Mig2, triggered by activation of Rim101 and Snf1. Pho89 is a high-affinity sodium/phosphate cotransporter belonging to the PHO regulon. Apart from being upregulated by Pho4, under alkaline condi