RESUMEN

A persistent question in evolutionary biology is how complex phenotypes evolve and whether phenotypic transitions are reversible. Multiple losses of floral pigmentation have been documented in the angiosperms, but color re-gain has not yet been described, supporting that re-gain is unlikely. Pollinator-mediated selection in Petunia has resulted in several color shifts comprised of both losses and gains of color. The R2R3-MYB transcription factor AN2 has been identified as a major locus responsible for shifts in pollinator preference. Whereas the loss of visible color has previously been attributed to repeated pseudogenization of AN2, here, we describe the mechanism of an independent re-gain of floral color via AN2 evolution. In P. secreta, purple color is restored through the improbable resurrection of AN2 gene function from a non-functional AN2-ancestor by a single reading-frame-restoring mutation. Thus, floral color evolution in Petunia is mechanistically dependent on AN2 functionality, highlighting its role as a hotspot in color transitions and a speciation gene for the genus.

Asunto(s)

Evolución Biológica , Petunia/genética , Pigmentos Biológicos/genética , Polinización , Flores/fisiología , Especiación Genética , Petunia/fisiología , Pigmentación/genética , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Factores de Transcripción/genética , Factores de Transcripción/metabolismo

RESUMEN

KEY MESSAGE: Chromosome regions affecting grain yield, grain yield components and plant water status were identified and validated in fall-sown spring wheats grown under full and limited irrigation. Increases in wheat production are required to feed a growing human population. To understand the genetic basis of grain yield in fall-sown spring wheats, we performed a genome-wide association study (GWAS) including 262 photoperiod-insensitive spring wheat accessions grown under full and limited irrigation treatments. Analysis of molecular variance showed that 4.1% of the total variation in the panel was partitioned among accessions originally developed under fall-sowing or spring-sowing conditions, 11.7% among breeding programs within sowing times and 84.2% among accessions within breeding programs. We first identified QTL for grain yield, yield components and plant water status that were significant in at least three environments in the GWAS, and then selected those that were also significant in at least two environments in a panel of eight biparental mapping populations. We identified and validated 14 QTL for grain yield, 15 for number of spikelets per spike, one for kernel number per spike, 11 for kernel weight and 9 for water status, which were not associated with differences in plant height or heading date. We detected significant correlations among traits and colocated QTL that were consistent with those correlations. Among those, grain yield and plant water status were negatively correlated in all environments, and six QTL for these traits were colocated or tightly linked (< 1 cM). QTL identified and validated in this study provide useful information for the improvement of fall-sown spring wheats under full and limited irrigation.

Asunto(s)

Grano Comestible/crecimiento & desarrollo , Sitios de Carácter Cuantitativo , Triticum/crecimiento & desarrollo , Triticum/genética , Agua , Grano Comestible/genética , Estudios de Asociación Genética , Genotipo , Desequilibrio de Ligamiento , Fenotipo , Estaciones del Año

RESUMEN

New races of Puccinia striiformis f. sp. tritici (Pst), the causal pathogen of wheat stripe rust, show high virulence to previously deployed resistance genes and are responsible for large yield losses worldwide. To identify new sources of resistance we performed a genome-wide association study (GWAS) using a worldwide collection of 1000 spring wheat accessions. Adult plants were evaluated under field conditions in six environments in the western United States, and seedlings were tested with four Pst races. A single-nucleotide polymorphism (SNP) Infinium 9K-assay provided 4585 SNPs suitable for GWAS. High correlations among environments and high heritabilities were observed for stripe rust infection type and severity. Greater levels of Pst resistance were observed in a subpopulation from Southern Asia than in other groups. GWAS identified 97 loci that were significant for at least three environments, including 10 with an experiment-wise adjusted Bonferroni probability < 0.10. These 10 quantitative trait loci (QTL) explained 15% of the phenotypic variation in infection type, a percentage that increased to 45% when all QTL were considered. Three of these 10 QTL were mapped far from previously identified Pst resistance genes and QTL, and likely represent new resistance loci. The other seven QTL mapped close to known resistance genes and allelism tests will be required to test their relationships. In summary, this study provides an integrated view of stripe rust resistance resources in spring wheat and identifies new resistance loci that will be useful to diversify the current set of resistance genes deployed to control this devastating disease.

Asunto(s)

Basidiomycota/patogenicidad , Resistencia a la Enfermedad/genética , Genoma de Planta , Triticum/genética , Estudio de Asociación del Genoma Completo , Polimorfismo de Nucleótido Simple , Poliploidía , Sitios de Carácter Cuantitativo , Triticum/inmunología , Triticum/microbiología

RESUMEN

BACKGROUND: Genes involved in arbuscular mycorrhizal (AM) symbiosis have been identified primarily by mutant screens, followed by identification of the mutated genes (forward genetics). In addition, a number of AM-related genes has been identified by their AM-related expression patterns, and their function has subsequently been elucidated by knock-down or knock-out approaches (reverse genetics). However, genes that are members of functionally redundant gene families, or genes that have a vital function and therefore result in lethal mutant phenotypes, are difficult to identify. If such genes are constitutively expressed and therefore escape differential expression analyses, they remain elusive. The goal of this study was to systematically search for AM-related genes with a bioinformatics strategy that is insensitive to these problems. The central element of our approach is based on the fact that many AM-related genes are conserved only among AM-competent species. RESULTS: Our approach involves genome-wide comparisons at the proteome level of AM-competent host species with non-mycorrhizal species. Using a clustering method we first established orthologous/paralogous relationships and subsequently identified protein clusters that contain members only of the AM-competent species. Proteins of these clusters were then analyzed in an extended set of 16 plant species and ranked based on their relatedness among AM-competent monocot and dicot species, relative to non-mycorrhizal species. In addition, we combined the information on the protein-coding sequence with gene expression data and with promoter analysis. As a result we present a list of yet uncharacterized proteins that show a strongly AM-related pattern of sequence conservation, indicating that the respective genes may have been under selection for a function in AM. Among the top candidates are three genes that encode a small family of similar receptor-like kinases that are related to the S-locus receptor kinases involved in sporophytic self-incompatibility. CONCLUSIONS: We present a new systematic strategy of gene discovery based on conservation of the protein-coding sequence that complements classical forward and reverse genetics. This strategy can be applied to diverse other biological phenomena if species with established genome sequences fall into distinguished groups that differ in a defined functional trait of interest.

Asunto(s)

Biología Computacional , Evolución Molecular , Regulación de la Expresión Génica de las Plantas , Magnoliopsida/genética , Magnoliopsida/microbiología , Micorrizas/fisiología , Proteínas de Plantas/genética , Perfilación de la Expresión Génica , Magnoliopsida/metabolismo , Filogenia , Proteínas de Plantas/metabolismo , Regiones Promotoras Genéticas/genética , Simbiosis

RESUMEN

BACKGROUND: Differences in floral traits, such as petal color, scent, morphology, or nectar quality and quantity, can lead to specific interactions with pollinators and may thereby cause reproductive isolation. Petunia provides an attractive model system to study the role of floral characters in reproductive isolation and speciation. The night-active hawkmoth pollinator Manduca sexta relies on olfactory cues provided by Petunia axillaris. In contrast, Petunia exserta, which displays a typical hummingbird pollination syndrome, is devoid of scent. The two species can easily be crossed in the laboratory, which makes it possible to study the genetic basis of the evolution of scent production and the importance of scent for pollinator behavior. RESULTS: In an F2 population derived from an interspecific cross between P. axillaris and P. exserta, we identified two quantitative trait loci (QTL) that define the difference between the two species' ability to produce benzenoid volatiles. One of these loci was identified as the MYB transcription factor ODORANT1. Reciprocal introgressions of scent QTL were used for choice experiments under controlled conditions. These experiments demonstrated that the hawkmoth M. sexta prefers scented plants and that scent determines choice at a short distance. When exposed to conflicting cues of color versus scent, the insects display no preference, indicating that color and scent are equivalent cues. CONCLUSION: Our results show that scent is an important flower trait that defines plant-pollinator interactions at the level of individual plants. The genetic basis underlying such a major phenotypic difference appears to be relatively simple and may enable rapid loss or gain of scent through hybridization.

Asunto(s)

Flores/química , Especiación Genética , Manduca/fisiología , Odorantes/análisis , Petunia/genética , Polinización/fisiología , Sitios de Carácter Cuantitativo/genética , Animales , Conducta Apetitiva/fisiología , Cromatografía de Gases , Cruzamientos Genéticos , Flores/genética , Genética de Población , Espectrometría de Masas , Petunia/fisiología , Polinización/genética , Especificidad de la Especie , Factores de Transcripción/genética , Compuestos Orgánicos Volátiles/análisis

RESUMEN

Two linkage maps were constructed for the model plant Petunia. Mapping populations were obtained by crossing the wild species Petunia axillaris subsp. axillaris with Petunia inflata, and Petunia axillaris subsp. parodii with Petunia exserta. Both maps cover the seven chromosomes of Petunia, and span 970 centimorgans (cM) and 700 cM of the genomes, respectively. In total, 207 markers were mapped. Of these, 28 are multilocus amplified fragment length polymorphism (AFLP) markers and 179 are gene-derived markers. For the first time we report on the development and mapping of 83 Petunia microsatellites. The two maps retain the same marker order, but display significant differences of recombination frequencies at orthologous mapping intervals. A complex pattern of genomic rearrangements was detected with the related genome of tomato (Solanum lycopersicum), indicating that synteny between Petunia and other Solanaceae crops has been considerably disrupted. The newly developed markers will facilitate the genetic characterization of mutants and ecological studies on genetic diversity and speciation within the genus Petunia. The maps will provide a powerful tool to link genetic and genomic information and will be useful to support sequence assembly of the Petunia genome.

Asunto(s)

Mapeo Cromosómico/métodos , Genoma de Planta/genética , Petunia/genética , Solanum lycopersicum/genética , Análisis del Polimorfismo de Longitud de Fragmentos Amplificados , Cromosomas de las Plantas/genética , Cruzamientos Genéticos , ADN de Plantas/genética , Especiación Genética , Variación Genética , Repeticiones de Microsatélite/genética , Petunia/clasificación , Polimorfismo Genético , Sintenía

RESUMEN

Most terrestrial plants form arbuscular mycorrhiza (AM), mutualistic associations with soil fungi of the order Glomeromycota. The obligate biotrophic fungi trade mineral nutrients, mainly phosphate (P(i) ), for carbohydrates from the plants. Under conditions of high exogenous phosphate supply, when the plant can meet its own P requirements without the fungus, AM are suppressed, an effect which could be interpreted as an active strategy of the plant to limit carbohydrate consumption of the fungus by inhibiting its proliferation in the roots. However, the mechanisms involved in fungal inhibition are poorly understood. Here, we employ a transcriptomic approach to get insight into potential shifts in metabolic activity and symbiotic signalling, and in the defence status of plants exposed to high P(i) levels. We show that in mycorrhizal roots of petunia, a similar set of symbiosis-related genes is expressed as in mycorrhizal roots of Medicago, Lotus and rice. P(i) acts systemically to repress symbiotic gene expression and AM colonization in the root. In established mycorrhizal roots, P(i) repressed symbiotic gene expression rapidly, whereas the inhibition of colonization followed with a lag of more than a week. Taken together, these results suggest that P(i) acts by repressing essential symbiotic genes, in particular genes encoding enzymes of carotenoid and strigolactone biosynthesis, and symbiosis-associated phosphate transporters. The role of these effects in the suppression of symbiosis under high P(i) conditions is discussed.

Asunto(s)

Micorrizas/fisiología , Petunia/microbiología , Fosfatos/farmacología , Raíces de Plantas/genética , Etiquetas de Secuencia Expresada , Perfilación de la Expresión Génica , Regulación de la Expresión Génica de las Plantas , Biblioteca de Genes , Análisis de Secuencia por Matrices de Oligonucleótidos , Petunia/genética , Petunia/fisiología , Raíces de Plantas/microbiología , Raíces de Plantas/fisiología , Simbiosis , Transcripción Genética

RESUMEN

Agricultural crops benefit from resistance to pathogens that endures over years and generations of both pest and crop. Durable disease resistance, which may be partial or complete, can be controlled by several genes. Some of the most devastating fungal pathogens in wheat are leaf rust, stripe rust, and powdery mildew. The wheat gene Lr34 has supported resistance to these pathogens for more than 50 years. Lr34 is now shared by wheat cultivars around the world. Here, we show that the LR34 protein resembles adenosine triphosphate-binding cassette transporters of the pleiotropic drug resistance subfamily. Alleles of Lr34 conferring resistance or susceptibility differ by three genetic polymorphisms. The Lr34 gene, which functions in the adult plant, stimulates senescence-like processes in the flag leaf tips and edges.

Asunto(s)

Transportadoras de Casetes de Unión a ATP/genética , Transportadoras de Casetes de Unión a ATP/metabolismo , Ascomicetos/patogenicidad , Basidiomycota/patogenicidad , Enfermedades de las Plantas , Triticum/genética , Triticum/microbiología , Transportadoras de Casetes de Unión a ATP/química , Secuencia de Aminoácidos , Ascomicetos/genética , Basidiomycota/genética , Mapeo Cromosómico , Cromosomas de las Plantas/genética , Clonación Molecular , Exones , Genes de Plantas , Inmunidad Innata , Datos de Secuencia Molecular , Mutación , Enfermedades de las Plantas/inmunología , Enfermedades de las Plantas/microbiología , Hojas de la Planta/microbiología , Proteínas de Plantas/química , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Polimorfismo de Nucleótido Simple , Sitios de Carácter Cuantitativo , Triticum/crecimiento & desarrollo , Triticum/inmunología

RESUMEN

Brachypodium sylvaticum and Brachypodium distachyon were recently proposed as new model plants because of their small genomes and their phylogenetic position between rice and Triticeae crops. We sequenced a 371-kb region in B. sylvaticum, the largest genomic sequence available so far from this species, providing quantitative data on gene conservation, collinearity and phylogeny. We compared it with orthologous regions from rice and wheat. Brachypodium and wheat show perfect macro-collinearity of genetic markers, whereas rice contains an approximately 220-kb inversion. Rice contains almost twice as many genes as Brachypodium in the region studied, whereas wheat has about 40% more. Through comparative annotation, we identified alternative transcripts and improved the annotation for several rice genes, indicating that approximately 15% of rice genes might require re-annotation. Surprisingly, our data suggest that 10-15% of functional sequences in small grass genomes may not encode any proteins. From available genomic and expressed sequence tag sequences, we estimated Brachypodium to have diverged from wheat about 35-40 Mya, significantly more recently than the divergence of rice and wheat. However, our data also indicate that orthologous regions from Brachypodium and wheat differ considerably in gene content, thus the Brachypodium genome sequence probably cannot replace genomic studies in the large Triticeae genomes.

Asunto(s)

Genoma de Planta , Oryza/genética , Poaceae/genética , Triticum/genética , Biología Computacional/métodos , Etiquetas de Secuencia Expresada , Genómica/métodos , Datos de Secuencia Molecular , Análisis de Secuencia de ADN

RESUMEN

Hexaploid wheat (Triticum aestivum L.) originated about 8,000 years ago from the hybridization of tetraploid wheat with diploid Aegilops tauschii Coss. containing the D-genome. Thus, the bread wheat D-genome is evolutionary young and shows a low degree of polymorphism in the bread wheat gene pool. To increase marker density around the durable leaf rust resistance gene Lr34 located on chromosome 7DS, we used molecular information from the orthologous region in rice. Wheat expressed sequence tags (wESTs) were identified by homology with the rice genes in the interval of interest, but were monomorphic in the 'Arina' x 'Forno' mapping population. To derive new polymorphic markers, bacterial artificial chromosome (BAC) clones representing a total physical size of approximately 1 Mb and belonging to four contigs were isolated from Ae. tauschii by hybridization screening with wheat ESTs. Several BAC clones were low-pass sequenced, resulting in a total of approximately 560 kb of sequence. Ten microsatellite sequences were found, and three of them were polymorphic in our population and were genetically mapped close to Lr34. Comparative analysis of marker order revealed a large inversion between the rice genome and the wheat D-genome. The SWM10 microsatellite is closely linked to Lr34 and has the same allele in the three independent sources of Lr34: 'Frontana', 'Chinese Spring', and 'Forno', as well in most of the genotypes containing Lr34. Therefore, SWM10 is a highly useful marker to assist selection for Lr34 in breeding programs worldwide.

Asunto(s)

Repeticiones de Minisatélite , Poaceae/genética , Alelos , Mapeo Cromosómico , Cromosomas Artificiales Bacterianos , Etiquetas de Secuencia Expresada , Marcadores Genéticos , Genoma de Planta , Inmunidad Innata/genética , Repeticiones de Microsatélite , Hibridación de Ácido Nucleico , Oryza/genética , Polimorfismo Genético , Poliploidía , Análisis de Secuencia de ADN , Triticum/genética