The antioxidative response, where ascorbate peroxidase (APX) is a key enzyme, is an integral part of the plant tolerance response to environmental stresses. As a first step towards the study of the physiological role and the regulation of the members of the Apx gene family, the orthologs of the stress-sensitive cultivated tomato Solanum lycopersicum cv. M82 (Slm) and of the wild salt-tolerant species S. pennellii acc. Atico (Spa) were identified by utilizing the tomato EST database, and characterized. A redundant list of 16 virtual Apx transcripts and four singleton ESTs was shown to correspond to seven genuine Apx genes. The complete tomato Apx gene family is comprised of genes encoding three cytosolic, two peroxisomal, and two chloroplastic APXs. These genes attained differential regulatory patterns in various Slm organs. More detailed study of Apx1 and Apx2 genes, that are the products of a recent gene duplication event, shows that they have already attained differential regulation within and between Slm and Spa under control and stress conditions. It is also suggested that due to lineage-specific gene duplication and lose events, intricate phylogenetic relationships exist among the members of the Apx gene families.

The development of the vertebrate hindbrain requires multiple coordinated signals which act via several pathways. One such signal is Fibroblast Growth Factor (FGF), which is necessary for the patterning of a major transcription factor in the hindbrain, Krox20. However, in the chick, it is still not known which specific FGF ligand is responsible for the regulation of Krox20 and how the signal is dispatched. The most characterized signaling pathway which FGF acts through in the nervous system is the MAPK/Erk1/2 pathway. Nevertheless, a detailed analysis of the hindbrain distribution of various components of this pathway has not been fully described. In this study we present a comprehensive atlas of the FGF ligands, receptors and members of the MAPK/Erk1/2 signaling components in subsequent stages of avian hindbrain development. Moreover, we show that FGF is a major signaling pathway that contributes to the activation of ERK1/2 and expression of the downstream targets Pea3 and Erm. Central to this study, we provide multiple evidence that FGF3 is required for the upregulation of Pea3 that in turn is necessary for Krox20 distribution in rhombomeres 3 and 5. These results show for the first time that Pea3 mediates the FGF3 signal to regulate the hindbrain expression of Krox20.

Background: During formation of the vertebrate central nervous system, the hindbrain is organized into segmental units, called rhombomeres (r). These cell-lineage restricted segments are separated by a subpopulation of cells known as boundary cells. Boundary cells display distinct molecular and cellular properties such as an elongated shape, enriched extracellular matrix components and a reduced proliferation rate compared to intra-rhombomeric cells. However, little is known regarding their functions and the mechanisms that regulate their formation.

SummaryCompartment boundaries act as organizing centers that segregate adjacent areas into domains of gene expression and regulation, and control their distinct fates via the secretion of signalling factors. During hindbrain development, a specialized cell-population forms boundaries between rhombomeres. These boundary cells demonstrate unique morphological properties and express multiple genes that differs them from intra-rhombomeric cells. Yet, little is known regarding the mechanisms that controls the expression or function of these boundary markers.Multiple components of the FGF signaling system, including ligands, receptors, downstream effectors as well as proteoglycans are shown to localize to boundary cells in the chick hindbrain. These patterns raise the possibility that FGF signaling plays a role in regulating boundary properties. We provide evidence to the role of FGF signaling, particularly the boundary-derived FGF3, in regulating the expression of multiple markers at hindbrain boundaries. These findings enable further characterization of the unique boundary-cell population, and expose a new function for FGFs as regulators of boundary-gene expression in the chick hindbrain.

The growth habit of lateral shoots (also termed “branching habit”) is an important descriptive and agronomic character of peanut. Yet, both the inheritance of branching habit and the genetic mechanism that controls it in this crop remain unclear. In addition, the low degree of polymorphism among cultivated peanut varieties hinders fine-mapping of this and other traits in non-homozygous genetic structures. Here, we combined high-throughput sequencing with a well-defined genetic system to study these issues in peanut. Initially, segregating F2 populations derived from a reciprocal cross between very closely related Virginia-type peanut cultivars with spreading and bunch growth habits were examined. The spreading/bunch trait was shown to be controlled by a single gene with no cytoplasmic effect. That gene was named Bunch1 and was significantly correlated with pod yield per plant, time to maturation and the ratio of “dead-end” pods. Subsequently, bulked segregant analysis was performed on 52 completely bunch, and 47 completely spreading F3 families. In order to facilitate the process of SNP detection and candidate-gene analysis, the transcriptome was used instead of genomic DNA. Young leaves were sampled and bulked. Reads from Illumina sequencing were aligned against the peanut reference transcriptome and the diploid genomes. Inter-varietal SNPs were detected, scored and quality-filtered. Thirty-four candidate SNPs were found to have a bulk frequency ratio value >10 and 6 of those SNPs were found to be located in the genomic region of linkage group B5. Three best hits from that over-represented region were further analyzed in the segregating population. The trait locus was found to be located in a ~1.1 Mbp segment between markers M875 (B5:145,553,897; 1.9 cM) and M255 (B5:146,649,943; 2.25 cM). The method was validated using a population of recombinant inbreed lines of the same cross and a new DNA SNP-array. This study demonstrates the relatively straight-forward utilization of bulk segregant analysis for trait fine-mapping in the low polymeric and heterozygous germplasm of cultivated peanut and provides a baseline for candidate gene discovery and map-based cloning of Bunch1.

SUMMARYComplex patterns and networks of genes coordinate rhombomeric identities, hindbrain segmentation and neuronal differentiation and are responsible for later brainstem functions. Pax6 is a highly conserved transcription factor crucial for neuronal development, yet little is known regarding its early roles during hindbrain segmentation. We show that Pax6 expression is highly dynamic in rhombomeres, suggesting an early function in the hindbrain. Utilization of multiple gain-and loss-of-function approaches in chick and mice revealed that loss of Pax6 disrupts the sharp expression borders of Krox20, Kreisler, Hoxa2, Hoxb1 and EphA and leads to their expansion into adjacent territories, whereas excess Pax6 reduces these expression domains. A mutual negative cross-talk between Pax6 and Krox20 allows these genes to be co-expressed in the hindbrain through regulation of the Krox20-repressor gene Nab1 by Pax6. Rhombomere boundaries are also distorted upon Pax6 manipulations, suggesting a mechanism by which Pax6 acts to set hindbrain segmentation. Finally, FGF signaling acts upstream of the Pax6-Krox20 network to regulate Pax6 segmental expression. This study unravels a novel role for Pax6 in the segmental organization of the early hindbrain and provides new evidence for its significance in regional organization along the central nervous system.

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