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The common garden petunia, Petunia hybrida, is derived from P. integrifolia and P. axillaris, two of many Petunia species endemic to South America. The geographic distribution includes temperate and subtropical regions of Argentina, Uruguay, Paraguay, Bolivia, and Brazil, with a center of diversity in southern Brazil. The presence of seven chromosomes and a number of morphological, anatomical, and biochemical characteristics differentiate the genus from its sister taxon, Calibrachoa. Included in this chapter is a taxononomic guide for the 14 currently recognized species, some of them restricted to very small geographic areas. Species diversity is in danger of diminishing significantly due to human intervention, particularly in the form of grassland destruction.
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... O gênero Petunia Juss. (Solanaceae) é composto por 16 espécies e mundialmente conhecido pela espécie ornamental P. hybrida, um híbrido de P. axillaris e um membro do clado de P. integrifolia (Stehmann et al. 2009;Segatto et al. 2014a;Bombarely et al. 2016). ...
... As espécies do gênero estão distribuídas nas regiões subtropicais e temperadas da América do Sul, com dois centros de diversidade no sul do Brasil: a Serra do Sudeste, no bioma Pampa, e a Serra Geral de Santa Catarina, no domínio Mata Atlântica (Stehmann et al. 2009). ...
... As espécies do gênero são diploides, possuem o mesmo número cromossômico 2n=14 (Stehmann et al. 2009) e baixa diversidade genética (Kulcheski et al. 2006;Lorenz-Lemke et al. 2006;Stehmann et al. 2009;Longo et al. 2014). Petunia apresenta grande diversificação floral e de polinizadores, além de intervalos geográficos de distribuição e especificidade de habitat para algumas espécies (Fregonezi et al. 2013). ...
Thesis
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With advancements in DNA sequencing technologies, evolutionary biologists realized that hybridization between different evolutionary lineages is far more frequent than previously imagined, playing a crucial role in the diversification of species. The effects of hybridization encompass a wide spectrum of consequences: it can lead species to extinction due to genetic disruption, or lead to speciation and adaptive alleles introgression, allowing the colonization of new environments. In this thesis, we aimed to investigate the role of hybridization in the evolutionary history of Petunia and its related genera, Calibrachoa and Fabiana. Petunia serves as a model system for phylogeography and speciation studies in South America due to its wide geographic distribution and remarkable species diversity. To achieve our objectives, we employed single nucleotide polymorphisms (SNP) data acquired through genotyping-by-sequencing (GBS) and transcriptomes from multiple species. Each chapter addressed the hybridization topic from distinct perspectives: in chapter 1, we explored gene flow in two species of the short corolla tube clade in a transitional zone between biomes; in chapter 2, we analyzed the hybridization between two subspecies of P. axillaris and the implications for the taxa conservation in the context of climate change; in chapter 3, we investigated the potential hybrid origin of a population exhibiting corolla color variation and discussed the speciation process in a Petunia hotspot; in Chapter 4, we examined the effects of sampling admixed individuals on species delimitation; and in chapter 5, we employed transcriptomic data from species of Petunia, Calibrachoa, and Fabiana to understand the reasons underlying the phylogenetic tree discordance in this clade. Our results indicated that interspecific gene flow was common and recurrent within the group, but these signals can be challenging to discern due to the high degree of incomplete lineage sorting (ILS) resulting from the rapid diversification. This thesis has shed light on the process of diversification and speciation within a charismatic group of South American plants, underscoring how hybridization is an essential mechanism that must be considered when seeking to understand the evolutionary history of plants.
Article
Background and aims Species delimitation can be challenging when analysing recently diverged species, especially those taxonomically synonymised due to morphological similarities. We aimed to untangle the relationships between two grassland species, Petunia guarapuavensis and Petunia scheideana, exploring the dynamics of fast divergence and addressing their species delimitation. Methods We used a low-coverage genome sequencing and population genomic approach to distinguish species and populations between P. guarapuavensis and P. scheideana. Our analysis focused on detecting structuration, hybridisation/introgression, and phylogenetic patterns. We employed demographic models to support species delimitation while exploring potential phylogeographic barriers influencing gene flow. Key Results Our findings indicated differentiation between the two species and revealed another lineage, which was phylogenetically distinct from the others and had no evidence of gene flow with them. The presence of a river acted as a phylogeographic barrier, limiting gene flow and allowing for structuration between closely related lineages. The optimal species delimitation scenario involved secondary contact between well-established lineages. Conclusions The rapid divergence observed in these Petunia species explains the lack of significant morphological differences, as floral diagnostic traits in species sharing the pollinators tend to evolve more slowly. This study highlights the complexity of species delimitation in recently diverged groups and emphasises the importance of genomic approaches in understanding evolutionary relationships and speciation dynamics.
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This experiment was carried out in the Laboratory of Plant Cells and Tissue Culture of the Horticulture and Landscaping Design Department/College of Agriculture/University of Kirkuk-Iraq, to study micropropagation of Petunia plant ( Petunia hybrida L.), different plant parts (Explants) were used (shoot tips and nodes) from petunia plants grown in the Agricultural Research and Experiments Station Al-Sayada. The explants were cultured on MS medium supplemented with Benzyl adenine at (0.0, 0.5, 1.0, 1.5, and 2.0) mg.l ⁻¹ and Kinetin at (0.0, 2.0, 4.0, 6.0, and 8.0) mg.l ⁻¹ at initiation and multiplication stages, Data refers highest response (100%) were obtained from all treatments of BA and Kin under study at initiation stage. highest number of branches, Length of the longest branch, total leaves number,(3.00 branches.part ⁻¹ , 3.15cm, 31.40 leaves.plantlet ⁻¹ ) respectively obtained from culture on MS medium supplemented with BA at 1.0 mg.l ⁻¹ , while the best rate of leaves number/longest branch 14.87 leaves.branch. ⁻¹ at 1.5 mg.l ⁻¹ . While in multiplication stage after 8 weeks, number of branches and number of leaves/longest branch (8.25 branches.part ⁻¹ , and 31.37 leaves.branch ⁻¹ ) respectively were obtained from culture on medium supplemented with BA at 1.5 mg.L ⁻¹ . Length of the longest branch and total leaves number (5.27cm and 52.90 leaves.plantlet ⁻¹ ) respectively were obtained from culture on medium at 1.0 mg.L ⁻¹ . Moreover, the highest number of branches, Length of the longest branch, total leaves number, and number of leaves/longest branch (3.25 branches.part ⁻¹ , 23.00 leaves.plantlet ⁻¹ , and 15.75 leaves.branch ⁻¹ ) respectively obtained from culture on MS medium supplemented with Kin at (6.0) mg.L ⁻¹ at initiation stage, while Length of the longest branch 3.11 cm were obtained by Kin at 4.0 mg.L ⁻¹ . For the multiplication stage, the rates were (4.00 branches.part ⁻¹ , 34.33 leaves.plantlet ⁻¹ , and 19.66 leaves. branch ⁻¹ ) respectively obtained from Kin at 4.0 mg.L ⁻¹ , while Length of the longest branch (4.12cm were obtained from culture on medium supplemented with Kin at 2.0 mg.L ⁻¹ .
Article
Despite the overarching history of species divergence, phylogenetic studies often reveal distinct topologies across regions of the genome. The sources of these gene tree discordances are variable, but incomplete lineage sorting (ILS) and hybridization are among those with the most biological importance. Petunia serves as a classic system for studying hybridization in the wild. While field studies suggest that hybridization is frequent, the extent of reticulation within Petunia and its closely related genera has never been examined from a phylogenetic perspective. In this study, we used transcriptomic data from 11 Petunia, 16 Calibrachoa, and 10 Fabiana species to illuminate the relationships between these species and investigate whether hybridization played a significant role in the diversification of the clade. We inferred that gene tree discordance within genera is linked to hybridization events along with high levels of ILS due to their rapid diversification. Moreover, network analyses estimated deeper hybridization events between Petunia and Calibrachoa, genera that have different chromosome numbers. Although these genera cannot hybridize at the present time, ancestral hybridization could have played a role in their parallel radiations, as they share the same habitat and life history.
Article
Closely related and young species often show high morphological similarity, challenging their identification and correct assignment. Molecular markers and integrative approaches have contributed to solving many taxonomic uncertainties. In this study, we evaluated the genetic variability and ecological features of Petunia guarapuavensis and Petunia scheideana, over which there is a taxonomic debate. Both species are endemic and rare, distributed in the subtropical highland grasslands in southern South America. We based our analyses on nuclear microsatellite and plastid sequences, aiming to disentangle the taxonomic ambiguities that made some consider these entities synonymous despite occupying different clades in the genus phylogenetic tree. Our findings support that there is genetic differentiation between these species, suggesting that they are independent taxonomic entities despite sharing floral traits and a few molecular polymorphisms. The low genetic sharing between the species is likely due to a common ancestor and recent divergence time. In contrast, their morphological similarity can be attributed to the absence of selective pressure, as both grow under similar ecological conditions. This study emphasizes that adding more than one sequence per species, combining data with dissimilar inheritance patterns, and exploring data through different methodologies help to disentangle taxonomic incongruences and reveal diversity that might otherwise remain hidden.
Article
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Background Theory suggests that the genetic architecture of traits under divergent natural selection influences how easily reproductive barriers evolve and are maintained between species. Divergently selected traits with a simple genetic architecture (few loci with major phenotypic effects) should facilitate the establishment and maintenance of reproductive isolation between species that are still connected by some gene flow. While empirical support for this idea appears to be mixed, most studies test the influence of trait architectures on reproductive isolation only indirectly. Petunia plant species are, in part, reproductively isolated by their different pollinators. To investigate the genetic causes and consequences of this ecological isolation, we deciphered the genetic architecture of three floral pollination syndrome traits in naturally occurring hybrids between the widespread Petunia axillaris and the highly endemic and endangered P. exserta. Results Using population genetics, Bayesian linear mixed modelling and genome-wide association studies, we found that the three pollination syndrome traits vary in genetic architecture. Few genome regions explain a majority of the variation in flavonol content (defining UV floral colour) and strongly predict the trait value in hybrids irrespective of interspecific admixture in the rest of their genomes. In contrast, variation in pistil exsertion and anthocyanin content (defining visible floral colour) is controlled by many genome-wide loci. Opposite to flavonol content, the genome-wide proportion of admixture between the two species predicts trait values in their hybrids. Finally, the genome regions strongly associated with the traits do not show extreme divergence between individuals representing the two species, suggesting that divergent selection on these genome regions is relatively weak within their contact zones. Conclusions Among the traits analysed, those with a more complex genetic architecture are best maintained in association with the species upon their secondary contact. We propose that this maintained genotype–phenotype association is a coincidental consequence of the complex genetic architectures of these traits: some of their many underlying small-effect loci are likely to be coincidentally linked with the actual barrier loci keeping these species partially isolated upon secondary contact. Hence, the genetic architecture of a trait seems to matter for the outcome of hybridization not only then when the trait itself is under selection.
Article
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The mechanisms of reproductive isolation that cause phenotypic diversification and eventually speciation are a major topic of evolutionary research. Hybrid necrosis is a post-zygotic isolation mechanism in which cell death develops in the absence of pathogens. It is often due to the incompatibility between proteins from two parents. Here we describe a unique case of hybrid necrosis due to an incompatibility between loci on chromosomes 2 and 7 between two pollinator-isolated Petunia species. Typical immune responses as well as endoplasmic reticulum stress responses are induced in the necrotic line. The locus on chromosome 2 encodes ChiA1, a bifunctional GH18 chitinase/lysozyme. The enzymatic activity of ChiA1 is dispensable for the development of necrosis. We propose that the extremely high expression of ChiA1 involves a positive feedback loop between the loci on chromosomes 2 and 7. ChiA1 is tightly linked to major genes involved in the adaptation to different pollinators, a form of pre-zygotic isolation. This linkage of pre- and post-zygotic barriers strengthens reproductive isolation and probably contributes to rapid diversification and speciation.
Article
Climate changes and associated glacial and interglacial cycles during the Quaternary strongly influenced the evolutionary history of countless number of species. Subtropical highland grasslands (SHG) in southern South America constitute a distinct vegetation type with high diversity and endemism rates. The most recent common ancestor of the genus Petunia (Solanaceae) originated in lowland grasslands, and some lineages secondarily migrated to SHG. Here, we describe the evolutionary history of an SHG species, P. altiplana, distributed throughout a wide area in a river-fragmented landscape. We used plastid and nuclear markers to evaluate the role of the Pelotas River and Quaternary climate cycles over the genetic structure and historical demography of this species based on a phylogeographical approach. We found moderate population expansions during the last 25 kyr, with a more recent (c. 1.6 kya) divergence between two groups of populations from opposite river margins, possibly caused by the expansion of the Araucaria Forest along the river valley, effectively isolating distinct grassland patches.
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Plant varieties exhibiting unstable or variegated phenotypes, or showing virus recovery have long remained a mystery. It is only with the development of transgenic plants 40 years ago that the epigenetic features underlying these phenomena were elucidated. Indeed, the study of transgenic plants that did not express the introduced sequences revealed that transgene loci sometimes undergo transcriptional gene silencing (TGS) or post-transcriptional gene silencing (PTGS) by activating epigenetic defenses that naturally control transposable elements, duplicated genes or viruses. Even when they do not trigger TGS or PTGS spontaneously, stably expressed transgenes driven by viral promoters set apart from endogenous genes in their epigenetic regulation. As a result, transgenes driven by viral promoters are capable of undergoing systemic PTGS throughout the plant, whereas endogenous genes can only undergo local PTGS in cells where RNA quality control is impaired. Together, these results indicate that the host genome distinguishes self from non-self at the epigenetic level, allowing PTGS to eliminate non-self, and preventing PTGS to become systemic and kill the plant when it is locally activated against deregulated self.
Chapter
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RESUMO As diferentes coberturas vegetais ocorrentes na bacia fora m classificadas a partir de uma imagem orbital Landsat (bandas 3, 4 e 5), processada através do programa Idrisi, resultando (após confirmação de campo) em set e padrões de uso do solo. As formações vegetais ocorrentes são descritas sucintamente através do método de avaliação ecológica rápida, com especial destaque para os táxons endêmicos e/ou ameaçados. Também foram avaliados os principais fatores que ameaçam a conservação, segundo a mesma técnica. As principais pressões são as queimadas, o pastoreio excessivo e a coleta indiscriminada de plantas com interesse horticultural, principalmente os cactos. Os afloramentos de rocha são os hábitats mais importantes do ponto de vista da preservação d a flora ameaçada na bacia do arroio João Dias, principalmente nos locais inacessíveis ao gado, com destaque para Petunia exserta (Solanaceae), Parodia spp. e Frailea spp. (ambas Cactaceae). São feitas recomendações no sentido de minimizar os riscos a que a flora local está submetida, principalmente evitando ações que possam causar danos irreversíveis, protegendo os hábitats remanescentes e recuperando hábitats potenciais degradados pelo uso inadequado.
Chapter
To date, approximately 30 Petunia species have been described. Their geographic origin is South America, where the various species have been documented from collections made in Argentina, Brazil, Bolivia, Paraguay, and Uruguay. The majority of the species have been found in three Brazilian provinces: Parana, Santa Catarina, and Rio Grande do Sul, and in areas of the other countries, particularly in interior areas where they share a common border. Petunia species, described in the literature of the 1800’s, were commonly found along river banks in isolated areas, for example, at the mouth of the Rio de la Plata, the Rio Negro, and the Paraná. Petunia parodii, described by Steere in 1930, was only reported to occur in the Formosa province of Argentina. Petunia parviflora has been found in the above countries and also in Cuba, Mexico, and in the United States in New Jersey, California, Texas, Arizona, and Florida. Whether the plants of P. parviflora found in geographic locations outside of South America are indigenous ecotypes or have become established through seed and plant dispersal remains to be established. Contemporary ecological, adaptive, and evolutionary research studies of Petunia in the native habitat is a complete void.