Computational thinking (CT) uses concepts that are essential to computing and information science to solve problems, design and evaluate complex systems, and understand human reasoning and behavior. This way of thinking has important implications in computer sciences as well as in almost every other field. Therefore, we contend that CT should be taught in elementary schools and included in every university's educational curriculum. Several studies that measure the impact of teaching programming, analytical thinking, and CT have been conducted. In this review, we analyze and discuss findings from these studies and highlight the importance of learning programming with a focus on the development of CT skills at a young age. We also describe the tools that are available to improve the teaching of CT and provide a state-of-the-art overview of how programming is being taught at schools and universities in Colombia and around the world.
Go ´mez-Bahamo ´n et al. show that speciation is associated with changes in migratory behavior in fork-tailed flycatchers (Tyrannus savana). Divergence occurred through loss of migratory behavior of a single lineage. This mode of speciation likely occurred across New World flycatchers (Tyrannidae).
Xanthomonas axonopodis pv. manihotis (Xam) is the causal agent of bacterial blight of cassava, which is among the main components of human diet in Africa and South America. Current information about the molecular pathogenicity factors involved in the infection process of this organism is limited. Previous studies in other bacteria in this genus suggest that advanced draft genome sequences are valuable resources for molecular studies on their interaction with plants and could provide valuable tools for diagnostics and detection. Here we have generated the first manually annotated high-quality draft genome sequence of Xam strain CIO151. Its genomic structure is similar to that of other xanthomonads, especially Xanthomonas euvesicatoria and Xanthomonas citri pv. citri species. Several putative pathogenicity factors were identified, including type III effectors, cell wall-degrading enzymes and clusters encoding protein secretion systems. Specific characteristics in this genome include changes in the xanthomonadin cluster that could explain the lack of typical yellow color in all strains of this pathovar and the presence of 50 regions in the genome with atypical nucleotide composition. The genome sequence was used to predict and evaluate 22 variable number of tandem repeat (VNTR) loci that were subsequently demonstrated as polymorphic in representative Xam strains. Our results demonstrate that Xanthomonas axonopodis pv. manihotis strain CIO151 possesses ten clusters of pathogenicity factors conserved within the genus Xanthomonas. We report 126 genes that are potentially unique to Xam, as well as potential horizontal transfer events in the history of the genome. The relation of these regions with virulence and pathogenicity could explain several aspects of the biology of this pathogen, including its ability to colonize both vascular and non-vascular tissues of cassava plants. A set of 16 robust, polymorphic VNTR loci will be useful to develop a multi-locus VNTR analysis scheme for epidemiological surveillance of this disease.
Cassava bacterial blight, caused by Xanthomonas axonopodis pv. manihotis, is a widespread disease that affects cassava (Manihot esculenta). We collected 238 X. axonopodis pv. manihotis strains by intensively sampling single fields in four edaphoclimatic zones (ECZs) in Colombia. DNA polymorphism of different X. axonopodis pv. manihotis populations was assessed by restriction fragment length polymorphism (RFLP) analyses, repetitive sequence-based polymerase chain reaction (rep-PCR), and amplified fragment length polymorphism (AFLP) assays. Genetic diversity, phenetic relationships among strains, and the coefficient of genetic differentiation were determined. All strains were tested for aggressiveness on the susceptible cassava cv. MCOL 1522. Strains were also tested for virulence on cassava differentials adapted to the strains' respective ECZs. Our study showed that the Colombian X. axonopodis pv. manihotis population has a high degree of genetic diversity. The hierarchical analysis of diversity showed genotypic differentiation at all levels, among ECZs, among fields within ECZs, and among strains within fields planted to several cassava genotypes. New RFLP haplotypes were detected, leading to the characterization of a new pathotype. Dendrograms from AFLP were more robust than those from RFLP data. A close association between the strains' geographical origin and DNA polymorphism was obtained using RFLP and AFLP data. We suggest that the host played a role in causing pathogen differentiation.
We compared tomato defense responses to Phytophthora infestans in highly compatible and partially compatible interactions. The highly compatible phenotype was achieved with a tomato-specialized isolate of P. infestans, whereas the partially compatible phenotype was achieved with a nonspecialized isolate. As expected, there was induction of the hypersensitive response (HR) earlier during the partially compatible interaction. However, contrary to our expectation, pathogenesis-related (PR) gene expression was not stimulated sooner in the partially compatible interaction. While the level of PR gene expression was quite similar in the two interactions, the LeDES gene (which encodes an enzyme necessary for the production of divinyl ethers) was expressed at a much higher level in the partially compatible interaction at 48 h after inoculation. Host reaction to the different pathogen genotypes was not altered (compared with wild type) in mutant tomatoes that were ethylene-insensitive (Never-ripe) or those with reduced ability to accumulate jasmonic acid (def-1). Similarly, host reaction was not altered in NahG transgenic tomatoes unable to accumulate salicylic acid. These combined data indicate that partial resistance in tomato to P. infestans is independent of ethylene, jasmonic acid, and salicylic acid signaling pathways.
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