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Wolfgang Busch and colleagues report results of a genome-wide association study of developmental cell–type traits in Arabidopsis . They identify a new F-box gene, KUK , as a regulator of root meristem and cell length and show the feasibility of applying genome-wide association to the study of cellular traits. With the increased availability of high-resolution sequence information, genome-wide association (GWA) studies have become feasible in a number of species 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 . The vast majority of these studies are conducted in human populations, where it is difficult to provide strong evidence for the functional involvement of unknown genes that are identified using GWA. Here we used the model organism Arabidopsis thaliana to combine high-throughput confocal microscopy imaging of traits at the cellular level, GWA and expression analyses to identify genomic regions that are associated with developmental cell–type traits. We identify and characterize a new F-box gene, KUK , that regulates meristem and cell length. We further show that polymorphisms in the coding sequence are the major causes of KUK allele–dependent natural variation in root development. This work demonstrates the feasibility of GWA using cellular traits to identify causal genes for basic biological processes such as development.

A high-throughput assay is used to analyse 40,000 potential extracellular domain interactions of a large family of plant cell surface receptors (LRR-RKs) and provide a cell surface interaction network for these receptors. A network of cell surface interactions Cell surface receptors mediate communication between the interior of a cell and its external environment. Specifically, the extracellular domains (ECDs) of such receptors interact with external molecules. It is less clear how interactions between ECDs of different receptors help to form receptor complexes for signal transduction. Youssef Belkhadir and colleagues investigate systems-level organization of leucine-rich repeat receptor kinases (LRR-RKs)—a large family of plant cell surface receptors with roles in processes including plant defence and development. The authors use a high-throughput assay to study 40,000 potential ECD interactions. They develop a cell surface interaction network for these receptors and study its dynamics. The team demonstrate the power of this network for detecting biologically relevant interactions by predicting and validating the function of previously uncharacterized LRR-RKs in plant growth and immunity. The cells of multicellular organisms receive extracellular signals using surface receptors. The extracellular domains (ECDs) of cell surface receptors function as interaction platforms, and as regulatory modules of receptor activation 1 , 2 . Understanding how interactions between ECDs produce signal-competent receptor complexes is challenging because of their low biochemical tractability 3 , 4 . In plants, the discovery of ECD interactions is complicated by the massive expansion of receptor families, which creates tremendous potential for changeover in receptor interactions 5 . The largest of these families in Arabidopsis thaliana consists of 225 evolutionarily related leucine-rich repeat receptor kinases (LRR-RKs) 5 , which function in the sensing of microorganisms, cell expansion, stomata development and stem-cell maintenance 6 , 7 , 8 , 9 . Although the principles that govern LRR-RK signalling activation are emerging 1 , 10 , the systems-level organization of this family of proteins is unknown. Here, to address this, we investigated 40,000 potential ECD interactions using a sensitized high-throughput interaction assay 3 , and produced an LRR-based cell surface interaction network (CSI LRR ) that consists of 567 interactions. To demonstrate the power of CSI LRR for detecting biologically relevant interactions, we predicted and validated the functions of uncharacterized LRR-RKs in plant growth and immunity. In addition, we show that CSI LRR operates as a unified regulatory network in which the LRR-RKs most crucial for its overall structure are required to prevent the aberrant signalling of receptors that are several network-steps away. Thus, plants have evolved LRR-RK networks to process extracellular signals into carefully balanced responses.

The molecular mechanisms by which plants modulate their root growth rate (RGR) in response to nutrient deficiency are largely unknown. Using Arabidopsis thaliana accessions, we analyzed RGR variation under combinatorial mineral nutrient deficiencies involving phosphorus (P), iron (Fe), and zinc (Zn). While -P stimulated early RGR of most accessions, -Fe or -Zn reduced it. The combination of either -P-Fe or -P-Zn led to suppression of the growth inhibition exerted by -Fe or -Zn alone. Surprisingly, root growth responses of the reference accession Columbia (Col-0) were not representative of the species under -P nor -Zn. Using a systems approach that combines GWAS, network-based candidate identification, and reverse genetic screen, we identified new genes that regulate root growth in -P-Fe: VIM1, FH6, and VDAC3. Our findings provide a framework to systematically identifying favorable allelic variations to improve root growth, and to better understand how plants sense and respond to multiple environmental cues.

Low availability of Fe significantly limits crop yields in many parts of the world. However, it is largely unknown which genes and alleles adjust plant growth in Fe limited environments. Using natural variation of a geographically restricted panel of Arabidopsis thaliana accessions, we identify allelic variation at the FRO2 locus associated with root length under iron deficiency. We show that non-coding sequence variation at the FRO2 locus leads to variation of FRO2 transcript levels, as well as ferric chelate reductase activity, and is causal for a portion of the observed root length variation. These FRO2 allele dependent differences are coupled with altered seedling phenotypes grown on iron-limited soil. Overall, we show that these natural genetic variants of FRO2 tune its expression. These variants might be useful for improvement of agronomically relevant species under specific environmental conditions, such as in podzols or calcareous soils. Iron is an essential micronutrient for plants and a lack of iron availability limits crop yield in many parts of the world. Here the authors show that natural variation in root growth of Arabidopsis plants under iron deficiency can be caused by allelic variation at the FRO2 locus.

Iron is critical for host–pathogen interactions. While pathogens seek to scavenge iron to spread, the host aims at decreasing iron availability to reduce pathogen virulence. Thus, iron sensing and homeostasis are of particular importance to prevent host infection and part of nutritional immunity. While the link between iron homeostasis and immunity pathways is well established in plants, how iron levels are sensed and integrated with immune response pathways remains unknown. Here we report a receptor kinase SRF3, with a role in coordinating root growth, iron homeostasis and immunity pathways via regulation of callose synthases. These processes are modulated by iron levels and rely on SRF3 extracellular and kinase domains which tune its accumulation and partitioning at the cell surface. Mimicking bacterial elicitation with the flagellin peptide flg22 phenocopies SRF3 regulation upon low iron levels and subsequent SRF3-dependent responses. We propose that SRF3 is part of nutritional immunity responses involved in sensing external iron levels. Iron homeostasis is known to influence plant immune signaling. Here the authors characterize SRF3, a receptor kinase that acts as a negative regulator of callose synthesis, that is required for root responses to iron deficiency and pathogen signals.

Zinc is an essential micronutrient for all living organisms and is involved in a plethora of processes including growth and development, and immunity. However, it is unknown if there is a common genetic and molecular basis underlying multiple facets of zinc function. Here we used natural variation in Arabidopsis thaliana to study the role of zinc in regulating growth. We identify allelic variation of the systemic immunity gene AZI1 as a key for determining root growth responses to low zinc conditions. We further demonstrate that this gene is important for modulating primary root length depending on the zinc and defence status. Finally, we show that the interaction of the immunity signal azelaic acid and zinc level to regulate root growth is conserved in rice. This work demonstrates that there is a common genetic and molecular basis for multiple zinc dependent processes and that nutrient cues can determine the balance of plant growth and immune responses in plants.

The primary culprits are increasing atmospheric carbon dioxide and the rise in global temperature that together result in climate-related constraints such as drought and heat waves. Epigenetics study heritable changes in gene expression that do not involve modifications in the DNA sequence per se and arise in response to internal and external environmental cues. [...]mangrove trees fix up to 100 times more carbon than terrestrial forests and they do it in a more permanent manner. [...]they offer a unique and highly efficient way to mitigate climate change.

Plants display a high degree of phenotypic plasticity that allows them to tune their form and function to changing environments. The plant root system has evolved mechanisms to anchor the plant and to efficiently explore soils to forage for soil resources. Key to this is an enormous capacity for plasticity of multiple traits that shape the distribution of roots in the soil. Such root system architecture-related traits are determined by root growth rates, root growth direction, and root branching. In this review, we describe how the root system is constituted, and which mechanisms, pathways, and genes mainly regulate plasticity of the root system in response to environmental variation.

Roots are essential organs for higher plants. They provide the plant with nutrients and water, anchor the plant in the soil, and can serve as energy storage organs. One remarkable feature of roots is that they are able to adjust their growth to changing environments. This adjustment is possible through mechanisms that modulate a diverse set of root traits such as growth rate, diameter, growth direction and lateral root formation. The basis of these traits and their modulation are at the cellular level, where a multitude of genes and gene networks precisely regulate development in time and space and tune it to environmental conditions. This review first describes the root system and then presents fundamental work that has shed light on the basic regulatory principles of root growth and development. It then considers emerging complexities and how they have been addressed using systems-biology approaches, and then describes and argues for a systems-genetics approach. For reasons of simplicity and conciseness, this review is mostly limited to work from the model plant Arabidopsis thaliana, in which much of the research in root growth regulation at the molecular level has been conducted. While forward genetic approaches have identified key regulators and genetic pathways, systems-biology approaches have been successful in shedding light on complex biological processes, for instance molecular mechanisms involving the quantitative interaction of several molecular components, or the interaction of large numbers of genes. However, there are significant limitations in many of these methods for capturing dynamic processes, as well as relating these processes to genotypic and phenotypic variation. The emerging field of systems genetics promises to overcome some of these limitations by linking genotypes to complex phenotypic and molecular data using approaches from different fields, such as genetics, genomics, systems biology and phenomics.

Key messageTaPTST1, a wheat homolog of AtPTST1 containing CBM can interact with GBSSI and regulate starch metabolism in wheat endosperm.In cereal endosperm, native starch comprising amylose and amylopectin is synthesized by the coordinated activities of several pathway enzymes. Amylose in starch influences its physio-chemical properties resulting in several human health benefits. The Granule-Bound Starch Synthase I (GBSSI) is the most abundant starch-associated protein. GBSSI lacks dedicated Carbohydrate-binding module (CBM). Previously, Protein Targeting To Starch 1 (PTST1) was identified as a crucial protein for the localization of GBSSI to the starch granules in Arabidopsis. The function of its homologous protein in the wheat endosperm is not known. In this study, TaPTST1, an AtPTST1 homolog, containing a CBM and a coiled-coil domain was identified in wheat. Protein-coding nucleotide sequence of TaPTST1 from Indian wheat variety ‘C 306’ was cloned and characterized. Homology modelling and molecular docking suggested the potential interaction of TaPTST1 with glucans and GBSSI. The TaPTST1 expression was higher in wheat grain than the other tissues, suggesting a grain-specific function. In vitro binding assays demonstrated different binding affinities of TaPTST1 for native starch, amylose, and amylopectin. Furthermore, the immunoaffinity pull-down assay revealed that TaPTST1 directly interacts with GBSSI, and the interaction is mediated by a coiled-coil domain. The direct protein–protein interaction was further confirmed by bimolecular fluorescence complementation assay (BiFC) in planta. Based on our findings we postulate a functional role for TaPTST1 in starch metabolism by targeting GBSSI to starch granules in wheat endosperm.