Structural basis of tankyrase activation by polymerization.

The poly-ADP-ribosyltransferase tankyrase (TNKS, TNKS2) controls a wide range of disease-relevant cellular processes, including WNT-β-catenin signalling, telomere length maintenance, Hippo signalling, DNA damage repair and glucose homeostasis1,2. This has incentivized the development of tankyrase inhibitors. Notwithstanding, our knowledge of the mechanisms that control tankyrase activity has remained limited. Both catalytic and non-catalytic functions of tankyrase depend on its filamentous polymerization3-5. Here we report the cryo-electron microscopy reconstruction of a filament formed by a minimal active unit of tankyrase, comprising the polymerizing sterile alpha motif (SAM) domain and its adjacent catalytic domain. The SAM domain forms a novel antiparallel double helix, positioning the protruding catalytic domains for recurring head-to-head and tail-to-tail interactions. The head interactions are highly conserved among tankyrases and induce an allosteric switch in the active site within the catalytic domain to promote catalysis. Although the tail interactions have a limited effect on catalysis, they are essential to tankyrase function in WNT-β-catenin signalling. This work reveals a novel SAM domain polymerization mode, illustrates how supramolecular assembly controls catalytic and non-catalytic functions, provides important structural insights into the regulation of a non-DNA-dependent poly-ADP-ribosyltransferase and will guide future efforts to modulate tankyrase and decipher its contribution to disease mechanisms

Response of Potato Cultivars to Phosphate Fertilization in Tropical Soils with Different Phosphorus Availabilities

Potato cultivars have different strategies for dealing with phosphorus (P) deficiency in soil, and their response to P fertilization may vary because of differences in soil P availability. This study was performed to evaluate the effect of P fertilization rates (0, 125, 250, 500, and 1000 kg P2O5 per hectare) on the P uptake, fertilizer P recovery, tuber yield, and applied P use efficiency of five potato cultivars (Agata, Asterix, Atlantic, Markies, and Mondial) grown in Oxisols with low, medium, and high P availability in southeastern Brazil. The tuber yield of all potato cultivars increased similarly with increase in P fertilizer application up to rates of 500, 250, and 125 kg P2O5 per hectare in the soils with low, medium, and high P availability respectively. This increase was found despite the leaf P concentrations being lower than the deficiency limit of 2.5 g kg−1 only in the soil with low P availability in the absence of P fertilizer application. The application of phosphate fertilizer in the planting furrow resulted in a greater increase in the leaf P concentration, plant growth, P uptake, number of tubers per plant, tuber mean weight, tuber yield, and P removal of the potato crop grown in the soil with low P availability compared with soils with high P availability. In soil with high P availability, P application rates higher than 125 kg P2O5 per hectare did not increase the number, size, and yield of tubers. The cultivar Mondial had the highest tuber yield, fertilizer P recovery, and applied P use efficiency, especially at the lower P application rates, but at a specific initial P availability, all cultivars responded to the same P application rate. The results indicate that phosphate fertilizer recommendations should be adjusted on the basis of soil P availability, and that it is not necessary to use different criteria to evaluate the P-nutritional status for individual potato cultivars

Nutrient Uptake and Removal by Potato Cultivars as Affected by Phosphate Fertilization of Soils with Different Levels of Phosphorus Availability

ABSTRACT Studies in the past decades have focused on how tuber yield of potato grown on different types of soil is affected by phosphate fertilizer rates. However, little is known about the effects of phosphorus availability in the soil and of phosphate fertilization on nutrient uptake and removal by the main potato cultivars currently grown in Brazil. Thus, in this study we investigated the influence of P fertilization rates on dry matter (DM) yield and nutrient uptake and removal in five potato cultivars grown on soils with different levels of P availability. Experiments were conducted on soil with low (14 mg dm-3), medium (36 mg dm-3), and high (70 mg dm-3) P availability, in randomized complete blocks with a 5 × 5 factorial arrangement with four replications. The treatments consisted of five potato cultivars (Agata, Asterix, Atlantic, Markies, and Mondial) and five P rates (0, 125, 250, 500, and 1,000 kg ha-1 P2O5) applied in the planting furrow. In soils with low, medium, and high P availability, P fertilization increased plant growth and tuber DM yield up to rates of 500, 250, and 125 kg ha-1 P2O5, respectively. At a specific initial P availability, all potato cultivars responded to the same P rate for plant growth, tuber yield, and nutrient uptake and removal. At the highest P fertilization rates, leaf analysis showed that the nutritional status of potato plants was not significantly changed and no nutritional deficiency was induced, regardless of the soil P availability levels. However, in the soils with higher P availability, P fertilization decreased plant Mn and Zn and tuber Mn concentrations in a linear manner. The increases in the uptake of N, K, Ca, Mg, S, B, Cu, and Fe and the removal of most nutrients in response to P fertilization were related more to the increase in plant biomass and tuber DM yield than to changes in concentrations of these nutrients in the plant. Application of P at high rates in soil with high P availability caused luxury P uptake, which reduced Mn uptake by 10 % and prevented higher Zn uptake, by reducing plant Zn concentrations, despite the increase in plant biomass