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Wheat Grain Development Is Characterized by Remarkable Trehalose 6-Phosphate Accumulation Pregrain Filling: Tissue Distribution and Relationship to SNF1-Related Protein Kinase1 Activity

Trehalose 6-phosphate (T6P) is a sugar signal that regulates metabolism, growth, and development and inhibits the central regulatory SNF1-related protein kinase1 (SnRK1; AKIN10/AKIN11). To better understand the mechanism in wheat (Triticum aestivum) grain, we analyze T6P content and SnRK1 activities. T6P levels changed 178-fold 1 to 45 d after anthesis (DAA), correlating with sucrose content. T6P ranged from 78 nmol g−1 fresh weight (FW) pregrain filling, around 100-fold higher than previously reported in plants, to 0.4 nmol g−1 FW during the desiccation stage. In contrast, maximum SnRK1 activity changed only 3-fold but was inhibited strongly by T6P in vitro. To assess SnRK1 activity in vivo, homologs of SnRK1 marker genes in the wheat transcriptome were identified using Wheat Estimated Transcript Server. SnRK1-induced and -repressed marker genes were expressed differently pregrain filling compared to grain filling consistent with changes in T6P. To investigate this further maternal and filial tissues were compared pre- (7 DAA) and during grain filling (17 DAA). Strikingly, in vitro SnRK1 activity was similar in all tissues in contrast to large changes in tissue distribution of T6P. At 7 DAA T6P was 49 to 119 nmol g−1 FW in filial and maternal tissues sufficient to inhibit SnRK1; at 17 DAA T6P accumulation was almost exclusively endospermal (43 nmol g−1 FW) with 0.6 to 0.8 nmol T6P g−1 FW in embryo and pericarp. The data show a correlation between T6P and sucrose overall that belies a marked effect of tissue type and developmental stage on T6P content, consistent with tissue-specific regulation of SnRK1 by T6P in wheat grain.

The Trehalose 6-Phosphate/SnRK1 Signaling Pathway Primes Growth Recovery following Relief of Sink Limitation

The T6P/SnRK1 mechanism of growth regulation responds to sink growth restriction and recovery following low-temperature limitation. Trehalose 6-P (T6P) is a sugar signal in plants that inhibits SNF1-related protein kinase, SnRK1, thereby altering gene expression and promoting growth processes. This provides a model for the regulation of growth by sugar. However, it is not known how this model operates under sink-limited conditions when tissue sugar content is uncoupled from growth. To test the physiological importance of this model, T6P, SnRK1 activities, sugars, gene expression, and growth were measured in Arabidopsis (Arabidopsis thaliana) seedlings after transfer to cold or zero nitrogen compared with sugar feeding under optimal conditions. Maximum in vitro activities of SnRK1 changed little, but T6P accumulated up to 55-fold, correlating with tissue Suc content in all treatments. SnRK1-induced and -repressed marker gene expression strongly related to T6P above and below a threshold of 0.3 to 0.5 nmol T6P g−1 fresh weight close to the dissociation constant (4 µm) of the T6P/ SnRK1 complex. This occurred irrespective of the growth response to Suc. This implies that T6P is not a growth signal per se, but through SnRK1, T6P primes gene expression for growth in response to Suc accumulation under sink-limited conditions. To test this hypothesis, plants with genetically decreased T6P content and SnRK1 overexpression were transferred from cold to warm to analyze the role of T6P/SnRK1 in relief of growth restriction. Compared with the wild type, these plants were impaired in immediate growth recovery. It is concluded that the T6P/SnRK1 signaling pathway responds to Suc induced by sink restriction that enables growth recovery following relief of limitations such as low temperature.

Inhibition of SnRK1 by metabolites: Tissue-dependent effects and cooperative inhibition by glucose 1-phosphate in combination with trehalose 6-phosphate

SnRK1 of the SNF1/AMPK group of protein kinases is an important regulatory protein kinase in plants. SnRK1 was recently shown as a target of the sugar signal, trehalose 6-phosphate (T6P). Glucose 6-phosphate (G6P) can also inhibit SnRK1 and given the similarity in structure to T6P, we sought to establish if each could impart distinct inhibition of SnRK1. Other central metabolites, glucose 1-phosphate (G1P), fructose 6-phosphate and UDP-glucose were also tested, and additionally ribose 5-phosphate (R5P), recently reported to inhibit SnRK1 strongly in wheat grain tissue. For the metabolites that inhibited SnRK1, kinetic models show that T6P, G1P and G6P each provide distinct regulation (50% inhibition of SnRK1 at 5.4 μM, 480 μM, >1 mM, respectively). Strikingly, G1P in combination with T6P inhibited SnRK1 synergistically. R5P, in contrast to the other inhibitors, inhibited SnRK1 in green tissues only. We show that this is due to consumption of ATP in the assay mediated by phosphoribulokinase during conversion of R5P to ribulose-1,5-bisphosphate. The accompanying loss of ATP limits the activity of SnRK1 giving rise to an apparent inhibition of SnRK1. Inhibition of SnRK1 by R5P in wheat grain preparations can be explained by the presence of green pericarp tissue; this exposes an important caveat in the assessment of potential protein kinase inhibitors. Data provide further insight into the regulation of SnRK1 by metabolites.

Design and Analysis of Cognitive Interviews for Comparative Multinational Testing

This article summarizes the work of the Comparative Cognitive Testing Workgroup, an international coalition of survey methodologists interested in developing an evidence-based methodology for examining the comparability of survey questions within cross-cultural or multinational contexts. To meet this objective, it was necessary to ensure that the cognitive interviewing (CI) method itself did not introduce method bias. Therefore, the workgroup first identified specific characteristics inherent in CI methodology that could undermine the comparability of CI evidence. The group then developed and implemented a protocol addressing those issues. In total, 135 cognitive interviews were conducted by participating countries. Through the process, the group identified various interpretive patterns resulting from sociocultural and language-related differences among countries as well as other patterns of error that would impede comparability of survey data.

Immigration, Welfare and Care in Portugal: Mapping the New Plurality of Female Migration Trajectories

The role of migrant women as domestic and care workers is a main characteristic of the feminisation of migration to southern Europe. This article aims to understand how and why current patterns of female migration to Portugal are a key element, driving increased flows of domestic workers. The article focuses first on the path followed by Portugal in the fields of immigration, employment, welfare-state developments and care arrangements, and then presents results of a qualitative study on Brazilian immigrant women. Findings show that the new plurality of female migration trajectories is an important factor in explaining the rapid integration of immigrant women in the domestic sector. This does not mean, however, that a predominant ‘migrant in the family’ care model has emerged in Portugal. In contrast with other southern European countries, different policy perspectives and outcomes over the last three decades have made for a more diversified care model. National contexts in southern European countries must therefore be taken into account, since they provide particular conditions for the main forms and features of migrant domestic work.

Regulation of growth by the trehalose pathway: relationship to temperature and sucrose.

Carbon signaling can override carbon supply in the regulation of growth. At least some of this regulation is imparted by the sugar signal trehalose 6-phosphate (T6P) through the protein kinase, SnRK1. This signaling pathway regulates biosynthetic processes involved in growth under optimal growing conditions. Recently, using a seedling system we showed that under sub-optimal conditions, such as cold, carbon signaling by T6P/ SnRK1 enables recovery of growth following relief of the stress. The T6P/ SnRK1 mechanism thus could be selected as a means of improving low temperature tolerance. High-throughput automated Fv/Fm measurements provide a potential means to screen for T6P/ SnRK1, and here we confirm through measurements of Fv/Fm in rosettes that T6P promotes low temperature tolerance and recovery during cold to warm transfer. Further, to better understand the coordination between sugars, trehalose pathway, and temperature-dependent growth, we examine the interrelationship between sugars, trehalose phosphate synthase (TPS), and trehalose phosphate phosphatase (TPP) gene expression and T6P content in seedlings. Sucrose, particularly when fed exogenously, correlated well with TPS1 and TPPB gene expression, suggesting that these enzymes are involved in maintaining carbon flux through the pathway in relation to sucrose supply. However, when sucrose accumulated to higher levels under low temperature and low N, TPS1 and TPPB expression were less directly related to sucrose; other factors may also contribute to regulation of TPS1 and TPPB expression under these conditions. TPPA expression was not related to sucrose content and all genes were not well correlated with endogenous glucose. Our work has implications for understanding acclimation to sink-limited growth conditions such as low temperature and for screening cold-tolerant genotypes with altered T6P/ SnRK1 signaling.

A Highly Embryogenic Line of the Legume Model Medicago truncatula, M9–10a: Performance Under Water Deficit

We examined relationships between conductance to CO2 diffusion from stomatal cavities to the chloroplasts (mesophyll conductance, gm) and plasma membrane aquaporin contents in tobacco leaves acclimated to the long-term drought and those grown under enough irrigation. gm was determined from simultaneous analyses of CO2 gas exchange and chlorophyll fluorescence. Relative plasma membrane aquaporin content was immunochemically determined with an antibody of radish PIP2-type aquaporins. Leaf hydraulic conductivity was measured as a relative weight loss of leaf disks in 1 M sorbitol solution. gm in drought-acclimated plants was about two-third that in well-watered plants. On the other hand, relative aquaporin content on a leaf area basis was about 1.5 times lager in drought-acclimated than well-watered plants. When leaves were fed with 0.5 mM HgCl2, an inhibitor of aquaporins, gm and leaf hydraulic conductivity in well-watered plants were reduced by 20–30% while those in drought-acclimated plants were not significantly affected. These results suggest that a decrease in aquaporin activity leads to the reductions of gm in the long-term drought.