Biology subjects

Abreu, I.

Publications and source records attributed to Abreu, I..

3 recordsLinked to original sources

bioRxiv2018

SSU72 phosphatase is a telomere replication terminator

Telomeres, the protective ends of eukaryotic chromosomes, are replicated through concerted actions by conventional DNA polymerases and telomerase, though the regulation of this process is not fully understood. Telomere replication requires (C)-Stn1-Ten1, a telomere ssDNA-binding complex that is homologous to RPA. Here, we show that the evolutionarily conserved phosphatase Ssu72 is responsible for terminating the cycle of telomere replication in fission yeast. Ssu72 controls the recruitment of Stn1 to telomeres by regulating Stn1 phosphorylation at S74, a residue that lies within the conserved OB fold domain. Consequently, ssu72{Delta} mutants are defective in telomere replication and exhibit long 3 overhangs, which are indicative of defective lagging strand DNA synthesis. We also show that hSSU72 regulates telomerase activation in human cells by controlling the recruitment of hSTN1 to telomeres. Thus, in this study, we demonstrate a previously unknown yet conserved role for the phosphatase SSU72, whereby this enzyme controls telomere homeostasis by activating lagging strand DNA synthesis, thus terminating the cycle of telomere replication.

cell biology↗

bioRxiv2017

Medicago truncatula copper transporter1 (MtCOPT1) delivers copper for symbiotic nitrogen fixation

* Copper is an essential nutrient for symbiotic nitrogen fixation. This element is delivered by the host plant to the nodule, where membrane copper transporter would introduce it into the cell to synthesize cupro-proteins.\n\n* COPT family members in model legume Medicago truncatula were identified and their expression determined. Yeast complementation assays, confocal microscopy, and phenotypical characterization of a Tnt1 insertional mutant line were carried out in the nodule-specific M.truncatula COPT family member.\n\n* Medicago truncatula genome encodes eight COPT transporters. MtCOPT1 (Medtr4g019870) is the only nodule-specific COPT gene. It is located in the plasma membrane of the differentiation, interzone and early fixation zones. Loss of MtCOPT1 function results in a copper-mitigated reduction of biomass production when the plant obtains its nitrogen exclusively from symbiotic nitrogen fixation. Mutation of MtCOPT1 results in diminished nitrogenase activity in nodules, likely an indirect effect from the loss of a copper-dependent function, such as cytochrome oxidase activity in copt1-1 bacteroids.\n\n* These data are consistent with a model in which MtCOPT1 transports copper from the apoplast into nodule cells to provide copper for essential metabolic processes associated with symbiotic nitrogen fixation.

plant biology↗

bioRxiv2017

Medicago truncatula Zinc-Iron Permease6 provides zinc to rhizobia-infected nodule cells

AbstractZinc is a micronutrient required for symbiotic nitrogen fixation. It has been proposed that in model legume Medicago truncatula, zinc is delivered in a similar fashion as iron, i.e. by the root vasculature into the nodule and released in the infection/differentiation zone. There, zinc transporters must introduce this element into rhizobia-infected cells to metallate the apoproteins that use zinc as a cofactor. MtZIP6 (Medtr4g083570) is a M. truncatula Zinc-Iron Permease (ZIP) that is expressed only in roots and nodules, with the highest expression levels in the infection/differentiation zone. Immunolocalization studies indicate that it is located in the plasma membrane of rhizobia-infected cells in the nodule. Down-regulating MtZIP6 expression levels with RNAi does not result in any strong phenotype when plants are being watered with mineral nitrogen. However, these silenced plants displayed severe growth defects when they depended on nitrogen fixed by their nodules, as a consequence of the loss of 80% of their nitrogenase activity. The reduction of this activity was not the result of iron not reaching the nodule, but an indirect effect of zinc being retained in the infection/differentiation zone and not reaching the cytosol of rhizobia-infected cells. These data are consistent with a model in which MtZIP6 would be responsible for zinc uptake by rhizobia-infected nodule cells in the infection/differentiation zone.

plant biology↗