Mapping Quantitative Trait Loci for Lettuce Resistance to <i>Verticillium dahliae</i> Race 3, Plant Development, and Leaf Color Using an Ultra-High-Density Bin Map Constructed from F <sub>2</sub> Progeny

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Abstract

Verticillium wilt is one of the most devastating soilborne diseases in lettuce, and the use of host resistance is the most optimal choice for its management. This study focused on identifying and mapping the genetic loci for resistance against Verticillium dahliae race 3 in a mapping population of 200 F _2:3 families developed from a cross between moderately resistant red-leaf lettuce ‘Sentry’ and susceptible green-leaf lettuce ‘La Brillante’. The population was genotyped using the tunable genotyping-by-sequencing (tGBS) approach. An ultra-high-density genetic linkage map containing 34,838 single nucleotide polymorphism markers grouped into 1,734 bins was constructed using F ₂ progeny and a sliding window approach. Three quantitative trait loci (QTLs) for resistance to V. dahliae race 3 were located on linkage groups (LGs) LG 2 ( qVR3-2.1) and LG 4 ( qVR3-4.1 and qVR3-4.2). Each of these QTLs explained up to ∼10% of the total phenotypic variation for the trait. At each locus, the resistance alleles were derived from cultivar Sentry that is partially resistant to the pathogen. Additional loci resistant to the disease are expected in this population, and transgressive segregation indicates that some of those loci could originate from the susceptible cultivar La Brillante. In addition, two QTLs for plant development were identified on LG 2 ( qIPD-2.1) and LG 7 ( qIPD-7.1), although no relationship was detected between resistance in these genotypes and the rate of plant growth. A major effect of QTL for red leaf color was detected on LG 9 ( qRLC-9.1). Candidate genes linked to some of the QTLs for V. dahliae race 3 resistance, plant development, and leaf color were identified. The QTLs for resistance identified in Sentry could diversify the resistance gene pool and provide an alternative tool to manage a newly emerged V. dahliae race 3.

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Sarvajeet Gill, Narendra Tuteja (2010)

Various abiotic stresses lead to the overproduction of reactive oxygen species (ROS) in plants which are highly reactive and toxic and cause damage to proteins, lipids, carbohydrates and DNA which ultimately results in oxidative stress. The ROS comprises both free radical (O(2)(-), superoxide radicals; OH, hydroxyl radical; HO(2), perhydroxy radical and RO, alkoxy radicals) and non-radical (molecular) forms (H(2)O(2), hydrogen peroxide and (1)O(2), singlet oxygen). In chloroplasts, photosystem I and II (PSI and PSII) are the major sites for the production of (1)O(2) and O(2)(-). In mitochondria, complex I, ubiquinone and complex III of electron transport chain (ETC) are the major sites for the generation of O(2)(-). The antioxidant defense machinery protects plants against oxidative stress damages. Plants possess very efficient enzymatic (superoxide dismutase, SOD; catalase, CAT; ascorbate peroxidase, APX; glutathione reductase, GR; monodehydroascorbate reductase, MDHAR; dehydroascorbate reductase, DHAR; glutathione peroxidase, GPX; guaicol peroxidase, GOPX and glutathione-S- transferase, GST) and non-enzymatic (ascorbic acid, ASH; glutathione, GSH; phenolic compounds, alkaloids, non-protein amino acids and α-tocopherols) antioxidant defense systems which work in concert to control the cascades of uncontrolled oxidation and protect plant cells from oxidative damage by scavenging of ROS. ROS also influence the expression of a number of genes and therefore control the many processes like growth, cell cycle, programmed cell death (PCD), abiotic stress responses, pathogen defense, systemic signaling and development. In this review, we describe the biochemistry of ROS and their production sites, and ROS scavenging antioxidant defense machinery. Copyright © 2010 Elsevier Masson SAS. All rights reserved.

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Bethany Huot, Jian Yao, Beronda Montgomery … (2014)

Growth-defense tradeoffs are thought to occur in plants due to resource restrictions, which demand prioritization towards either growth or defense, depending on external and internal factors. These tradeoffs have profound implications in agriculture and natural ecosystems, as both processes are vital for plant survival, reproduction, and, ultimately, plant fitness. While many of the molecular mechanisms underlying growth and defense tradeoffs remain to be elucidated, hormone crosstalk has emerged as a major player in regulating tradeoffs needed to achieve a balance. In this review, we cover recent advances in understanding growth-defense tradeoffs in plants as well as what is known regarding the underlying molecular mechanisms. Specifically, we address evidence supporting the growth-defense tradeoff concept, as well as known interactions between defense signaling and growth signaling. Understanding the molecular basis of these tradeoffs in plants should provide a foundation for the development of breeding strategies that optimize the growth-defense balance to maximize crop yield to meet rising global food and biofuel demands. © The Author 2014. Published by the Molecular Plant Shanghai Editorial Office in association with Oxford University Press on behalf of CSPB and IPPE, SIBS, CAS.

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Xuehui Huang, Qi Feng, Qian Qian … (2009)

The next-generation sequencing technology coupled with the growing number of genome sequences opens the opportunity to redesign genotyping strategies for more effective genetic mapping and genome analysis. We have developed a high-throughput method for genotyping recombinant populations utilizing whole-genome resequencing data generated by the Illumina Genome Analyzer. A sliding window approach is designed to collectively examine genome-wide single nucleotide polymorphisms for genotype calling and recombination breakpoint determination. Using this method, we constructed a genetic map for 150 rice recombinant inbred lines with an expected genotype calling accuracy of 99.94% and a resolution of recombination breakpoints within an average of 40 kb. In comparison to the genetic map constructed with 287 PCR-based markers for the rice population, the sequencing-based method was approximately 20x faster in data collection and 35x more precise in recombination breakpoint determination. Using the sequencing-based genetic map, we located a quantitative trait locus of large effect on plant height in a 100-kb region containing the rice "green revolution" gene. Through computer simulation, we demonstrate that the method is robust for different types of mapping populations derived from organisms with variable quality of genome sequences and is feasible for organisms with large genome sizes and low polymorphisms. With continuous advances in sequencing technologies, this genome-based method may replace the conventional marker-based genotyping approach to provide a powerful tool for large-scale gene discovery and for addressing a wide range of biological questions.