Food for thought: how nutrients regulate root system architecture

The spatial arrangement of the plant root system (root system architecture, RSA) is very sensitive to edaphic and endogenous signals that report on the nutrient status of soil and plant. Signalling pathways underpinning RSA responses to individual nutrients, particularly nitrate and phosphate, have been unravelled. Researchers have now started to investigate interactive effects between two or more nutrients on RSA. Several proteins enabling crosstalk between signalling pathways have recently been identified. RSA is potentially an important trait for sustainable and/or marginal agriculture. It is generally assumed that RSA responses are adaptive and optimise nutrient uptake in a given environment, but hard evidence for this paradigm is still sparse. Here we summarize recent advances made in these areas of research

To respond or not to respond? Natural variation of root architectural responses to nutrient signals

The amino acid glutamate (Glu) acts as a fast excitatory neurotransmitter in mammals. Its importance in plant signalling was recognized with the discovery of channel proteins similar to mammalian Glu receptors, as well as distinct changes in root-system architecture in response to very small amounts of soil Glu. Based on natural genetic variation within Arabidopsis, Walch-Liu et al. (2017) have now identified a major locus underpinning this root response, as well as several loci controlling it through gene by environment interactions with nitrate and temperature. It is a significant step towards unraveling crosstalk between signalling pathways that enable plants to adjust their growth and development to multiple environmental stimuli

Natural variation at XND1 impacts root hydraulics and trade-off for stress responses in Arabidopsis

Soil water uptake by roots is a key component of plant performance and adaptation to adverse environments. Here, we use a genome-wide association analysis to identify the XYLEM NAC DOMAIN 1 (XND1) transcription factor as a negative regulator of Arabidopsis root hydraulic conductivity (Lp). The distinct functionalities of a series of natural XND1 variants and a single nucleotide polymorphism that determines XND1 translation efficiency demonstrate the significance of XND1 natural variation at species-wide level. Phenotyping of xnd1 mutants and natural XND1 variants show that XND1 modulates Lp through action on xylem formation and potential indirect effects on aquaporin function and that it diminishes drought stress tolerance. XND1 also mediates the inhibition of xylem formation by the bacterial elicitor flagellin and counteracts plant infection by the root pathogen Ralstonia solanacearum. Thus, genetic variation at XND1, and xylem differentiation contribute to resolving the major trade-off between abiotic and biotic stress resistance in Arabidopsis

Cryptic variation in RNA-directed DNA-methylation controls lateral root development when auxin signaling is perturbed

Maintaining the right balance between plasticity and robustness in biological systems is important to allow adaptation while maintaining essential functions. Developmental plasticity of plant root systems has been the subject of intensive research, but the mechanisms underpinning robustness remain unclear. Here, we show that potassium deficiency inhibits lateral root organogenesis by delaying early stages in the formation of lateral root primordia. However, the severity of the symptoms arising from this perturbation varies within a natural population of Arabidopsis and is associated with the genetic variation in CLSY1, a key component of the RNA-directed DNA-methylation machinery. Mechanistically, CLSY1 mediates the transcriptional repression of a negative regulator of root branching, IAA27, and promotes lateral root development when the auxin-dependent proteolysis pathway fails. Our study identifies DNA-methylation-mediated transcriptional repression as a backup system for post-translational protein degradation which ensures robust development and performance of plants in a challenging environment

Impact Of Job Status And Demographic Trends On Quality Education: A Case Study Of Private Universities In Pakistan

The major purpose of this paper was to examine the quality of various aspects of higher education in the private sector of Pakistan by adopting a descriptive method of research. The population of the study constituted 270 administrators, 6,180 teachers and 61,108 students in existing 54 private universities and degree-awarding institutions of Pakistan. The method of cluster sampling was used to select the study sample of 840 people, which was carried out in two stages. In the first stage, 12 clusters of universities were randomly chosen out of the total population of private universities. In the second stage, 60 administrators, 180 teachers and 600 students were selected through a random sampling procedure with five administrators, 15 teachers and 50 students from each selected cluster. Three questionnaires, developed and refined through pre-testing, were used as measuring instruments to collect data. The researcher personally visited each university and collected data from the sample. The collected data was tabulated, analyzed and interpreted by using ANOVA and t test techniques

Comparison Of The Frequency And Effectiveness Of Positive And Negative Reinforcement Practices In Schools

The major purpose of the study was to compare the frequency and effectiveness of positive and negative reinforcement practices deployed by teachers in boys’ and girls’ secondary schools in urban and rural areas. It was hypothesized that there would be no difference in use of reward and punishment by teachers in secondary schools in urban and rural areas with respect to their frequency and effectiveness. The results of this study brought out a clear picture of the reward and punishment practices being followed in schools, which may serve as a useful tool for improving these practices that influence development of students’ desired behaviour. The population of the study comprised of the teachers serving in government secondary schools of Punjab. A sample of 1,000 teachers (200 from district Rawalpindi, 150 from district Attock, 200 from district Lahore, 150 from district Gujranwala, 150 from district Multan, and 150 from district Khanewal) was randomly selected in such a way that the proportion of rural and urban boys’ and girls’ secondary school teachers was evenly balanced. In order to collect data from sample teachers, a comprehensive questionnaire was developed and personally administered. The data obtained was tabulated, analyzed and interpreted by using appropriate descriptive and inferential tests of significance, such as one-way chi-square and two-way chi-square. The level of significance was 0.05. On the basis of results and discussion, it was concluded that the teachers of urban schools had better knowledge of using reward and punishment with respect to their frequency and effectiveness as well. There should be a countrywide program to train teachers according to the demands of the new era

Phosphate and zinc transport and signalling in plants: toward a better understanding of their homeostasis interaction

Zn and Pi are essential elements for plant growth. Current understanding of the regulation of their homeostasis interaction and signalling cross-talk is presente

Protein kinase SnRK2. 4 is a key regulator of aquaporins and root hydraulics in Arabidopsis

Soil water uptake by roots is a key component of plant water homeostasis contributing to plant growth and survival under ever-changing environmental conditions. The water transport capacity of roots (root hydraulic conductivity; Lpr ) is mostly contributed by finely regulated Plasma membrane Intrinsic Protein (PIP) aquaporins. In this study, we used natural variation of Arabidopsis for the identification of quantitative trait loci (QTLs) contributing to Lpr . Using recombinant lines from a biparental cross (Cvi-0 x Col-0), we show that the gene encoding class 2 Sucrose-Non-Fermenting Protein kinase 2.4 (SnRK2.4) in Col-0 contributes to >30% of Lpr by enhancing aquaporin-dependent water transport. At variance with the inactive and possibly unstable Cvi-0 SnRK2.4 form, the Col-0 form interacts with and phosphorylates the prototypal PIP2;1 aquaporin at Ser121 and stimulates its water transport activity upon coexpression in Xenopus oocytes and yeast cells. Activation of PIP2;1 by Col-0 SnRK2.4 in yeast also requires its protein kinase activity and can be counteracted by clade A Protein Phosphatases 2C. SnRK2.4 shows all hallmarks to be part of core abscisic acid (ABA) signaling modules. Yet, long-term (>3 h) inhibition of Lpr by ABA possibly involves a SnRK2.4-independent inhibition of PIP2;1. SnRK2.4 also promotes stomatal aperture and ABA-induced inhibition of primary root growth. The study identifies a key component of Lpr and sheds new light on the functional overlap and specificity of SnRK2.4 with respect to other ABA-dependent or independent SnRK2s

The Five AhMTP1 Zinc Transporters Undergo Different Evolutionary Fates towards Adaptive Evolution to Zinc Tolerance in Arabidopsis halleri

Gene duplication is a major mechanism facilitating adaptation to changing environments. From recent genomic analyses, the acquisition of zinc hypertolerance and hyperaccumulation characters discriminating Arabidopsis halleri from its zinc sensitive/non-accumulator closest relatives Arabidopsis lyrata and Arabidopsis thaliana was proposed to rely on duplication of genes controlling zinc transport or zinc tolerance. Metal Tolerance Protein 1 (MTP1) is one of these genes. It encodes a Zn2+/H+ antiporter involved in cytoplasmic zinc detoxification and thus in zinc tolerance. MTP1 was proposed to be triplicated in A. halleri, while it is present in single copy in A. thaliana and A. lyrata. Two of the three AhMTP1 paralogues were shown to co-segregate with zinc tolerance in a BC1 progeny from a cross between A. halleri and A. lyrata. In this work, the MTP1 family was characterized at both the genomic and functional levels in A. halleri. Five MTP1 paralogues were found to be present in A. halleri, AhMTP1-A1, -A2, -B, -C, and -D. Interestingly, one of the two newly identified AhMTP1 paralogues was not fixed at least in one A. halleri population. All MTP1s were expressed, but transcript accumulation of the paralogues co-segregating with zinc tolerance in the A. halleri X A. lyrata BC1 progeny was markedly higher than that of the other paralogues. All MTP1s displayed the ability to functionally complement a Saccharomyces cerevisiæ zinc hypersensitive mutant. However, the paralogue showing the least complementation of the yeast mutant phenotype was one of the paralogues co-segregating with zinc tolerance. From our results, the hypothesis that pentaplication of MTP1 could be a major basis of the zinc tolerance character in A. halleri is strongly counter-balanced by the fact that members of the MTP1 family are likely to experience different evolutionary fates, some of which not concurring to increase zinc tolerance

Etude moléculaire des familles de gènes Metal Tolerance Protein 1(MTP1) et Plant Defensins Type I (PDF1): contribution à la compréhension des mécanismes moléculaires évolutifs liés à l'acquisition de la tolérance au zinc chez Arabidopsis halleri

A. halleri, is a model species to study molecular evolutionary mechanisms related to zinc hypertolerance and hyperaccumulation, due to its close relatedness with A. thaliana which is zinc sensitive and non-accumulator. Here, we comparatively characterised in both species, two zinc homeostasis and/or zinc tolerance related genes sub-families: the Metal Tolerance Protein 1 (MTP1) and the Plant defensins type I (PDF1). Genomic analyses revealed that the copy number of these genes is increased in A. halleri compared to A. thaliana. It was thus tempting to relate the acquisition of zinc hypertolerance in A. halleri to these gene duplications. However, the assumption was invalidated by functional analyses. For instance, some of the AhMTP1 or AhPDF1 proteins induced weak or no zinc tolerance to yeast. More importantly, transcripts of many AhMTP1 or AhPDF1 genes were either not accumulated or were very poorly expressed in A. halleri. These results indicate that different members of these gene sub-families are not equally functional. It is thus expected that these gene duplicates are undergoing different evolutionary fates regarding zinc tolerance. Besides helping to understand the molecular evolutionary mechanisms, studying zinc-related genes in A. halleri may also help developing strategies like phytoremediation and biofortification.A. halleri, est une espèce modèle pour l'étude des mécanismes moléculaires liés à l'évolution des caractères d'hypertolérance au zinc et d'hyperaccumulation de ce métal, car elle est phylogénétiquement proche d'A. thaliana qui est sensible au zinc et non-accumulatrice. Dans ce travail, nous avons caractérisé comparativement chez A. thaliana et chez A. halleri, deux sous-familles de gènes liés à l'homéostasie du zinc et ou à sa tolérance: Metal Tolérance Protein 1 (MTP1) et Plant Defensin type I (PDF1). Notre analyse génomique montre que le nombre de ces gènes est plus élevé chez A. halleri que chez A. thaliana confortant l'hypothèse actuelle reliant les duplications de gènes chez A. halleri à l'acquisition de son caractère d'hypertolérance. Mais, les résultats de nos études fonctionnelles ne vont pas dans ce sens, car ils montrent que, par exemple, certaines protéines AhMTP1 et AhPDF1 induisent une tolérance au zinc faible voire nulle lorsqu'elles sont testées dans la levure. Mais le résultat le plus marquant est que les transcrits de plusieurs gènes AhMTP1 et AhPDF1 ne sont pas détectables ou bien sont faiblement accumulés dans la plante. Nos résultats montrent donc que les gènes de ces sous-familles ne sont pas équivalents en ce qui concerne leur fonction dans la tolérance au zinc suggérant ainsi qu'ils sont le sujet de devenirs évolutifs différents. En dehors de leur contribution à la compréhension des mécanismes moléculaires qui sous-tendent l'évolution de la tolérance au zinc chez A. halleri, nos travaux sont également porteurs de développements biotechnologiques appliqués au zinc dans les domaines de la phytoremédiation et de la biofortification