Additive genetic variation of transcriptional regulation: metallothionein expression in the soil insect Orchesella cincta

Field-selected metal tolerance in Orchesella cincta is correlated with overexpression of the single copy cadmium (Cd) inducible metallothionein (mt). Previously, we have demonstrated large phenotypic variation in mt gene expression, and a higher frequency of high-expression phenotypes in a tolerant population. Here, we describe midparent-offspring regression analysis of mt gene expression in a laboratory culture originating from a noncontaminated natural population. Families were either not exposed (n=47) or exposed to 0.5 micromol Cd per gram dry food (n=46). Mean mt gene expressions normalized to 28S rRNA and beta-actin RNA were generated using real-time RT-PCR applied to parents and offspring RNA and subjected to regression analysis. A significant heritability (h2) for mt gene expression was estimated between 0.36 (beta-actin normalized) and 0.46 (28S normalized) in Cd exposed families. Nontreated families did not yield a significant h2 value. Restriction Fragment Length Polymorphism analysis of the metallothionein promoter sequence revealed eight promoter alleles that show structural variation. Three alleles show increased frequencies in families with high mt expression. Another gene, croquemort (isolated from a differential screening for 1 micromole Cd treatment) showed no h2 of gene expression in response to 0.5 micromol Cd. This gene codes for a receptor-protein involved in recognition of apoptotic cells and may participate in the general stress response. The present data suggest that evolution of metal tolerance in O. cincta can occur in the field by selection for high mt expression due to structural changes in mt cis-regulation.     

Control of plant growth and development through manipulation of cell-cycle genes

The plant embryo is a relatively simple structure consisting of a primordial shoot and root, whose development is frozen in the form of a seed. Most development of the mature plant takes place post-embryonically, and is the consequence of cell division and organogenesis in small regions known as meristems, which originate in the embryonic shoot and root apices. Significant recent progress has been made in understanding the mechanisms that control the plant cell cycle at a molecular level, and the first attempts have been made to control plant growth through modulation of cell-cycle genes. These results suggest that there is significant potential to control plant growth and architecture through manipulation of cell division rates. However, a full realisation of the promise of such strategies will probably require a much greater understanding of cell division control and how its upstream regulation is co-ordinated by spatial relationships between cells and by environmental signals.     

Triggering the cell cycle in plants

In essence, the mitotic cell cycle in eukaryotes involves the duplication and separation of chromosomes, coupled to the process of dividing one cell into two. Cytokinesis is therefore the culmination of a series of events that were triggered during G1 phase, and brings the daughter cells back to the starting position in G1 for another possible round of division. In all eukaryotes, progression through the cell cycle is controlled by cyclin-dependent kinases that bind to positive regulators called cyclins. This review explores some of the pathways that trigger the plant cell cycle, with emphasis on the G1 phase. Examples include signalling pathways involving glutathione and cellular redox potential, the possible existence of a G1 DNA-damage checkpoint, and the plant hormones auxin and cytokinin. Progress in understanding the link between cell proliferation, cell differentiation and the cell-cycle machinery in a developmental context is discussed.     

Characterization of a novel Agrobacterium tumefaciens galactarolactone cycloisomerase enzyme for direct conversion of D-galactarolactone to 3-deoxy-2-keto-L-threo-hexarate

Microorganisms use different pathways for D-galacturonate catabolism. In the known microbial oxidative pathway, D-galacturonate is oxidized to D-galactarolactone, the lactone hydrolyzed to galactarate, which is further converted to 3-deoxy-2-keto-hexarate and α-ketoglutarate. We have shown recently that Agrobacterium tumefaciens strain C58 contains an uronate dehydrogenase (At Udh) that oxidizes D-galacturonic acid to D-galactarolactone. Here we report identification of a novel enzyme from the same A. tumefaciens strain, which we named Galactarolactone cycloisomerase (At Gci) (E.C. 5.5.1.-), for the direct conversion of the D-galactarolactone to 3-deoxy-2-keto-hexarate. The At Gci enzyme is 378 amino acids long and belongs to the mandelate racemase subgroup in the enolase superfamily. At Gci was heterologously expressed in Escherichia coli, and the purified enzyme was found to exist as an octameric form. It is active both on D-galactarolactone and D-glucarolactone, but does not work on the corresponding linear hexaric acid forms. The details of the reaction mechanism were further studied by NMR and optical rotation demonstrating that the reaction product of At Gci from D-galactaro-1,4-lactone and D-glucaro-1,4-lactone conversion is in both cases the L-threo form of 3-deoxy-2-keto-hexarate.     

Isolation of Legionella pneumophila from pluvial floods by amoebal coculture

Viable Legionella pneumophila bacteria were isolated by amoebal coculture from pluvial floods after intense rainfall and from water collected at sewage treatment plants. Several isolated L. pneumophila strains belonged to sequence types that have been previously identified in patients.     

Studying the genetic basis of drought tolerance in sorghum by managed stress trials and adjustments for phenological and plant height differences

Managed environments in the form of well watered and water stressed trials were performed to study the genetic basis of grain yield and stay green in sorghum with the objective of validating previously detected QTL. As variations in phenology and plant height may influence QTL detection for the target traits, QTL for flowering time and plant height were introduced as cofactors in QTL analyses for yield and stay green. All but one of the flowering time QTL were detected near yield and stay green QTL. Similar co-localization was observed for two plant height QTL. QTL analysis for yield, using flowering time/plant height cofactors, led to yield QTL on chromosomes 2, 3, 6, 8 and 10. For stay green, QTL on chromosomes 3, 4, 8 and 10 were not related to differences in flowering time/plant height. The physical positions for markers in QTL regions projected on the sorghum genome suggest that the previously detected plant height QTL, Sb-HT9-1, and Dw2, in addition to the maturity gene, Ma5, had a major confounding impact on the expression of yield and stay green QTL. Co-localization between an apparently novel stay green QTL and a yield QTL on chromosome 3 suggests there is potential for indirect selection based on stay green to improve drought tolerance in sorghum. Our QTL study was carried out with a moderately sized population and spanned a limited geographic range, but still the results strongly emphasize the necessity of corrections for phenology in QTL mapping for drought tolerance traits in sorghum.     

A 3-year study reveals that plant growth stage, season and field site affect soil fungal communities while cultivar and GM-trait have minor effects

In this three year field study the impact of different potato (Solanum tuberosum L.) cultivars including a genetically modified (GM) amylopectin-accumulating potato line on rhizosphere fungal communities are investigated using molecular microbiological methods. The effects of growth stage of a plant, soil type and year on the rhizosphere fungi were included in this study. To compare the effects, one GM cultivar, the parental isoline, and four non-related cultivars were planted in the fields and analysed using T-RFLP on the basis of fungal phylum specific primers combined with multivariate statistical methods. Additionally, fungal biomass and some extracellular fungal enzymes (laccases, Mn-peroxidases and cellulases) were quantified in order to gain insight into the function of the fungal communities. Plant growth stage and year (and agricultural management) had the strongest effect on both diversity and function of the fungal communities while the GM-trait studied was the least explanatory factor. The impact of cultivar and soil type was intermediate. Occasional differences between cultivars, the amylopectin-accumulating potato line, and its parental variety were detected, but these differences were mostly transient in nature and detected either only in one soil, one growth stage or one year.     

Sources of dietary protein in relation to blood pressure in a general Dutch population

Background

Little is known about the relation of different dietary protein types with blood pressure (BP). We examined whether intake of total, plant, animal, dairy, meat, and grain protein was related to BP in a cross sectional cohort of 20,820 Dutch adults, aged 20–65 y and not using antihypertensive medication.

Design

Mean BP levels were calculated in quintiles of energy-adjusted protein with adjustment for age, sex, BMI, education, smoking, and intake of energy, alcohol, and other nutrients including protein from other sources. In addition, mean BP difference after substitution of 3 en% carbohydrates or MUFA with protein was calculated.

Results

Total protein and animal protein were not associated with BP (p_trend = 0.62 and 0.71 respectively), both at the expense of carbohydrates and MUFA. Systolic BP was 1.8 mmHg lower (p_trend<0.01) in the highest (>36 g/d) than in the lowest (<27 g/d) quintile of plant protein. This inverse association was present both at the expense of carbohydrates and MUFA and more pronounced in individuals with untreated hypertension (−3.6 mmHg) than in those with normal (+0.1 mmHg) or prehypertensive BP (−0.3 mmHg; p_interaction<0.01). Meat and grain protein were not related to BP. Dairy protein was directly associated with systolic BP (+1.6 mmHg, p_trend<0.01), but not with diastolic BP (p_trend = 0.24).

Conclusions

Total protein and animal protein were not associated with BP in this general untreated Dutch population. Plant protein may be beneficial to BP, especially in people with elevated BP. However, because high intake of plant protein may be a marker of a healthy diet and lifestyle in general, confirmation from randomized controlled trials is warranted.