An analysis of Pseudomonas genomic diversity in take-all infected wheat fields reveals the lasting impact of wheat cultivars on the soil microbiota.

Manipulation of the soil microbiota associated with crop plants has huge promise for the control of crop pathogens. However, to fully realize this potential we need a better understanding of the relationship between the soil environment and the genes and phenotypes that enable microbes to colonize plants and contribute to biocontrol. A recent 2 years of investigation into the effect of wheat variety on second year crop yield in the context of take-all fungal infection presented the opportunity to examine soil microbiomes under closely defined field conditions. Amplicon sequencing of second year soil samples showed that Pseudomonas spp. were particularly affected by the wheat cultivar grown in year one. Consequently, 318 rhizosphere-associated Pseudomonas fluorescens strains were isolated and characterized across a variety of genetic and phenotypic traits. Again, the wheat variety grown in the first year of the study was shown to exert considerable selective pressure on both the extent and nature of Pseudomonas genomic diversity. Furthermore, multiple significant correlations were identified within the phenotypic/genetic structure of the Pseudomonas population, and between individual genotypes and the external wheat field environment. The approach outlined here has considerable future potential for our understanding of plant-microbe interactions, and for the broader analysis of complex microbial communities.

Assessment of core and accessory genetic variation in Rhizobium leguminosarum symbiovar trifolii strains from diverse locations and host plants using PCR-based methods.

UNLABELLED: The nitrogen-fixing symbiosis between Rhizobium leguminosarum and host legumes is recognized as a key part of sustainable agriculture. A culture collection containing rhizobia isolated from legumes of economic importance in the UK and worldwide, maintained at Rothamsted Research for many years, provided material for this study. We aimed to develop and validate efficient molecular diagnostics to investigate whether the host plant or geographical location had a greater influence on the genetic diversity of rhizobial isolates, and the extent to which the core bacterial genome and the accessory symbiosis genes located on plasmids were affected. To achieve this, core housekeeping genes and those involved in symbiosis interactions were sequenced and compared with genome-sequenced strains in the public domain. Results showed that some Rh. leguminosarum symbiovar trifolii strains nodulating clovers and Rh. leguminosarum sv. viciae strains nodulating peas and vicias shared identical housekeeping genes, clover nodule isolates from the same location could have divergent symbiosis genes, and others isolated on different continents could be very similar. This illustrates the likely co-migration of rhizobia and their legume hosts when crops are planted in new areas and indicates that selective pressure may arise from both local conditions and crop host genotypes. SIGNIFICANCE AND IMPACT OF THE STUDY: The nitrogen-fixing symbiosis between Rhizobium leguminosarum and host legumes has been recognized as a key part of sustainable agriculture for many years; this study provides new tools to study rhizobial biogeography which will be invaluable for extending the cultivation of legumes and indicating whether or not inoculation is necessary.

Estimation of directional division frequencies in vascular cambium and in marginal meristematic cells of plants.

Using simple arithmetical formulae, it is shown that, when the meristematic initial cells of a growing plant organ are arranged in a ring, the cellular dimensions predict the relative frequencies of anticlinal and periclinal divisions which these cells undergo. The pattern of cell file branching which appears during the course of development, and which is predicted by this mathematical model, is validated using data pertaining to the numbers and dimensions of initial cells within the secondary vascular cambium of hybrid aspen trees. Data pertaining to a second, simpler set of initial cells which comprises the outer cellular ring of the thallus of the alga Coleochaete orbicularis, and from which all the radial cell files of the circular disc-like thallus are descended, have also been used for model validation. Combining the mathematical approach to division frequencies with data of actual cell sizes permits inferences about the course of the increase of the number of cell files (generated by the anticlinal divisions) and the number of cells within each file (generated by the periclinal divisions) during the earlier stages of secondary tissue or thallus development, and also about how they will develop at future stages. The question whether or not cell division patterns conform to the geometry of the system in which the cells are embedded is also discussed.

Effects of genotype, season, and nitrogen nutrition on gene expression and protein accumulation in wheat grain.

Six commercial U.K. cultivars of winter wheat selected to represent different abilities to partition nitrogen into grain protein were grown in replicated field trials at five different sites over three seasons. The proportion of LMW glutenin subunits decreased and the proportion of gliadins increased during grain development and in response to N application. Differences were observed between the proportions of LMW glutenin subunits and gliadins in low- and high-protein grain, these two fractions being decreased and increased, respectively. There was little effect of grain protein content on the proportions of either the HMW glutenin subunits or large glutenin polymers, which are enriched in these subunits, with the latter increasing during development in all cultivars. The proportion of total protein present in polymers in the mature grain decreased with increasing N level. Correlations were also observed between the abundances of gliadin protein transcripts and the corresponding proteins.

First-order differential equation models with estimable parameters as functions of environmental variables and their application to a study of vascular development in young hybrid aspen stems.

A novel method is described for solving systems of differential equations pertaining to organism development, where this development is assumed to be directly influenced by fluctuation in measurable environmental variables. The system parameters are written as functions of these variables and, because these functions involve the accumulation of "environment time" (e.g., "day-degrees"), the system is therefore regulated by the prevailing environmental conditions. This method contrasts with the more usual descriptions of development along a time-line. The parameters of the differential equations involved are estimated by modelling data, which show evidence of changes in the dependent variable(s), i.e. the components of the system. They are expressed in terms of their response to continuous fluctuations in one or more independent, environmental variables. Accumulated thermal time (including day-degrees) or more complex units may be derived by using either linear or nonlinear functions. Critical environmental parameters such as the basal thresholds of a given developmental process or parameters describing a nonlinear relationship with the environment may then be estimated. This paper develops the methodology of this environmentally driven approach to describing organism development in general terms, and gives a specific example of its application with reference to the cellular development within the secondary vascular tissues in the stems of young hybrid aspen trees.

Seasonal cold and circadian changes in blood pressure and physical activity in young and elderly people.

AIM: To test the hypothesis that there is no association between seasonal cold and the circadian responses of blood pressure, deep-body temperature and physical activity in healthy young and elderly men. METHODS: 25 healthy elderly (aged 70-82 years) and 21 young volunteers (aged 20-30 years) participated in a 3-year prospective cross-seasonal study. RESULTS: Ambulatory day-time blood pressures in the older men were higher in the winter than in the summer and higher in both seasons than in the young people. The seasonally related differences were associated with lower outdoor and indoor temperatures, lower body temperature and higher activity levels in the elderly group in the winter. The older but not the younger group had higher blood pressure and levels of physical activity at certain times of the day in the winter compared with the summer. CONCLUSION: Time-of-day winter increases in blood pressure in older people may be related to increased activity as well as to levels of ambient temperature. Although it is generally advantageous for older people to be physically active in order to prevent circulatory disease, there may be a rationale for advising that that they should avoid intense activity at certain times of the day, especially in the winter.