Responses of rice to chronic and acute iron toxicity: genotypic differences and biofortification aspects

Background and aims

Iron (Fe) toxicity is a wide-spread stress in lowland rice production. The aim of this study was to differentiate between responses to acute Fe stress during the vegetative stage and chronic Fe stress throughout the growing period.

Methods

Six rice genotypes were tested in a semi-artificial greenhouse setup, in which acute (almost 1500 mg L^?1 Fe in soil solution during the vegetative stage) and chronic (200 to 300 mg L^?1 Fe throughout the season) Fe toxicity were simulated.

Results

Acute Fe stress induced early development of heavy leaf bronzing, whereas moderate symptoms occurred in the chronic treatment throughout the season. Grain yields were only reduced in the chronic stress treatment (?23 %) due to reductions in spikelet fertility, grain number and grain weight. Symptom formation during the early growth stages did not reflect yield responses in all genotypes. Only one genotype showed increases in grain Fe concentrations (24 % in the acute stress and 44 % in the chronic stress) compared to the control.

Conclusions

Contrasting genotypes responded differently to acute and chronic Fe toxicity, and one genotype showed consistent tolerance and the ability to translocate excess Fe into grains. These traits can be useful in the adaptive breeding of rice for Fe toxic environments.

     

A QTL on chromosome 3q23 influences processing speed in humans

Processing speed is a psychological construct that refers to the speed with which an individual can perform any cognitive operation. Processing speed correlates strongly with general cognitive ability, declines sharply with age and is impaired across a number of neurological and psychiatric disorders. Thus, identifying genes that influence processing speed will likely improve understanding of the genetics of intelligence, biological aging and the etiologies of numerous disorders. Previous genetics studies of processing speed have relied on simple phenotypes (eg, mean reaction time) derived from single tasks. This strategy assumes, erroneously, that processing speed is a unitary construct. In the present study, we aimed to characterize the genetic architecture of processing speed by using a multidimensional model applied to a battery of cognitive tasks. Linkage and QTL‐specific association analyses were performed on the factors from this model. The randomly ascertained sample comprised 1291 Mexican‐American individuals from extended pedigrees. We found that performance on all three distinct processing‐speed factors (Psychomotor Speed; Sequencing and Shifting and Verbal Fluency) were moderately and significantly heritable. We identified a genome‐wide significant quantitative trait locus (QTL) on chromosome 3q23 for Psychomotor Speed (LOD = 4.83). Within this locus, we identified a plausible and interesting candidate gene for Psychomotor Speed (Z = 2.90, P = 1.86 × 10^?03).     

Autoinhibition Mechanism of the Ubiquitin-Conjugating Enzyme UBE2S by Autoubiquitination

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Tree shape‐based approaches for the comparative study of cophylogeny

Cophylogeny is the congruence of phylogenetic relationships between two different groups of organisms due to their long‐term interaction. We investigated the use of tree shape distance measures to quantify the degree of cophylogeny. We implemented a reverse‐time simulation model of pathogen phylogenies within a fixed host tree, given cospeciation probability, host switching, and pathogen speciation rates. We used this model to evaluate 18 distance measures between host and pathogen trees including two kernel distances that we developed for labeled and unlabeled trees, which use branch lengths and accommodate different size trees. Finally, we used these measures to revisit published cophylogenetic studies, where authors described the observed associations as representing a high or low degree of cophylogeny. Our simulations demonstrated that some measures are more informative than others with respect to specific coevolution parameters especially when these did not assume extreme values. For real datasets, trees’ associations projection revealed clustering of high concordance studies suggesting that investigators are describing it in a consistent way. Our results support the hypothesis that measures can be useful for quantifying cophylogeny. This motivates their usage in the field of coevolution and supports the development of simulation‐based methods, i.e., approximate Bayesian computation, to estimate the underlying coevolutionary parameters.     

Sorting and pooling strategy: a novel tool to map a virus proteome for CD8 T-cell epitopes

Human cytomegalovirus (CMV) is a major cause of morbidity in immunocompromised individuals. However, no efficient vaccine has been developed to date. Identification of T-cell target proteins and epitopes is crucial not only for developing a successful immunization strategy, but also for new approaches using adoptive transfer of antigen-specific T-cells. The CMV genome has more than 200 open reading frames potentially coding for as many proteins. Here, we describe a robust, fast, and simple SPOT synthesis strategy, which allowed us to micro-synthesize every possible CD8 T-cell epitope in the entire potential CMV proteome. So far, 9069 of these peptides have been tested in an ex vivo T-cell stimulation assay. As well as confirming a number of previously known epitopes, we identified several new ones.     

Heme binding properties of heterologously expressed spinach cytochrome b(6): implications for transmembrane b-type cytochrome formation

In vivo and in vitro requirements for the formation of cytochrome b(6) were examined to analyze the mechanisms of transmembrane b-type cytochrome formation. After heterologous expression of spinach cytochrome b(6), formation of the holo-cytochrome was observed within the E. coli inner membrane. The transmembrane orientation of cytochrome b(6) appeared not to be critical for heme binding and holo-cytochrome formation. Furthermore, in vitro reconstitution of cytochrome b(6) was possible under oxidizing as well as under reducing conditions. Taken together these observations strongly indicate that transmembrane b-type cytochromes can spontaneously assemble in vitro as well as in a membrane.