Molecular studies in olive (Olea europaea L.): overview on DNA markers applications and recent advances in genome analysis

Comprehensive Review of Olea europaea: A Holistic Exploration into Its Botanical Marvels, Phytochemical Riches, Therapeutic Potentials, and Safety Profile

Human health is now inextricably linked to lifestyle choices, which can either protect or predispose people to serious illnesses. The Mediterranean diet, characterized by the consumption of various medicinal plants and their byproducts, plays a significant role in protecting against ailments such as oxidative stress, cancer, and diabetes. To uncover the secrets of this natural treasure, this review seeks to consolidate diverse data concerning the pharmacology, toxicology, phytochemistry, and botany of Olea europaea L. (O. europaea). Its aim is to explore the potential therapeutic applications and propose avenues for future research. Through web literature searches (using Google Scholar, PubMed, Web of Science, and Scopus), all information currently available on O. europaea was acquired. Worldwide, ethnomedical usage of O. europaea has been reported, indicating its effectiveness in treating a range of illnesses. Phytochemical studies have identified a range of compounds, including flavanones, iridoids, secoiridoids, flavonoids, triterpenes, biophenols, benzoic acid derivatives, among others. These components exhibit diverse pharmacological activities both in vitro and in vivo, such as antidiabetic, antibacterial, antifungal, antioxidant, anticancer, and wound-healing properties. O. europaea serves as a valuable source of conventional medicine for treating various conditions. The findings from pharmacological and phytochemical investigations presented in this review enhance our understanding of its therapeutic potential and support its potential future use in modern medicine.

Assessment of population structure, genetic diversity and relationship of Mediterranean olive accessions using SSR markers and computational tools

Olive tree is an emblematic crop of the Mediterranean region, mainly renowned for its fruit oil, although the species provides several industrial purposes. The Mediterranean basin constitutes the origin of olive species diversification and represents a valuable source of genetic variability of olive germplasm. Therefore, the evaluation of the diversity and the population structure of this Mediterranean germplasm is a challenge for olive species preservation, crop breeding and genetic improvement. In this context, our study aims to analyze the genetic diversity and the population structure of 79 Mediterranean olive accessions using 15 genomic SSRs and by applying computational model-based approaches. The used SSRs revealed a total number of 225 alleles with a mean of 15 alleles per locus. Observed and expected heterozygosity (Ho = 0.79, He = 0.805) with a Polymorphism Information Content value of 0.775 indicate high level of genetic diversity. All results of the Unweighted Pair Group Method with Arithmetic (UPGMA), Jaccard similarity index, Principal Coordinate Analysis (PCoA) and the Bayesian analyses supported the separation of the Mediterranean varieties in two sub-populations, one of which mainly composed by Spanish accessions.

Quality assessment of leaf extracts of 12 olive cultivars and impact of seasonal variation based on UV spectroscopy and phytochemcial content using multivariate analyses

INTRODUCTION

Recently, focus has been made on the health-oriented uses of olive leaves, a byproduct of olive production, as a potential source of antioxidants. Oleuropein is one of the phenolic components in olive leaves known for its high antioxidant value.

OBJECTIVE

The main aim of the current study was constructing a model for the quality assessment of olive leaves and their potential phytochemical content and hence biological value as well. The phytochemical variation in olive leaves in both flowering (spring) and fruiting seasons (autumn) was also investigated.

METHODS

In this study, the leaves of 12 different olive cultivars from different geographical origins growing in Egypt were assessed for their oleuropein content, total flavonoid (TF) content and total polyphenol (Pph) content in spring and autumn via ultraviolet (UV) spectroscopy and high-performance liquid chromatography (HPLC) coupled to multivariate data analyses. The antioxidant activity of olive leaf extracts was assessed using 2,2'-diphenyl-1-picrylhydrazyl (DPPH) assay.

RESULTS

Higher levels of oleuropein, TF and Pph content were found in spring with the highest oleuropein content in the Spanish cultivar; Manzanillo, followed by the Italian cultivar Coratina and the Egyptian Agizi Okasi (218.94, 151.58 and 122.18 mg/100 g of dried leaf extract, respectively). UV spectra was also measured and the collected data were coupled to multivariate analyses showing clustering of cultivars with common geographical origin.

CONCLUSION

Our findings emphasised the influence of collection time and type of cultivar on the chemical profile of olive leaves. The model presented herein, serves for the quality assessment of olive leaves based on their phytochemical profile.

How to Choose a Good Marker to Analyze the Olive Germplasm (Olea europaea L.) and Derived Products

The olive tree (Olea europaea L.) is one of the most cultivated crops in the Mediterranean basin. Its economic importance is mainly due to the intense production of table olives and oil. Cultivated varieties are characterized by high morphological and genetic variability and present a large number of synonyms and homonyms. This necessitates the introduction of a rapid and accurate system for varietal identification. In the past, the recognition of olive cultivars was based solely on analysis of the morphological traits, however, these are highly influenced by environmental conditions. Therefore, over the years, several methods based on DNA analysis were developed, allowing a more accurate and reliable varietal identification. This review aims to investigate the evolving history of olive tree characterization approaches, starting from the earlier morphological methods to the latest technologies based on molecular markers, focusing on the main applications of each approach. Furthermore, we discuss the impact of the advent of next generation sequencing and the recent sequencing of the olive genome on the strategies used for the development of new molecular markers.

Coupling the endophytic microbiome with the host transcriptome in olive roots

The connection between olive genetic responses to environmental and agro-climatic conditions and the composition, structure and functioning of host-associated, belowground microbiota has never been studied under the holobiont conceptual framework. Two groups of cultivars growing under the same environmental, pedological and agronomic conditions, and showing highest (AH) and lowest (AL) Actinophytocola relative abundances, were earlier identified. We aimed now to: i) compare the root transcriptome profiles of these two groups harboring significantly different relative abundances in the above-mentioned bacterial genus; ii) examine their rhizosphere and root-endosphere microbiota co-occurrence networks; and iii) connect the root host transcriptome pattern to the composition of the root microbial communities by correlation and co-occurrence network analyses. Significant differences in olive gene expression were found between the two groups. Co-occurrence networks of the root endosphere microbiota were clearly different as well. Pearson's correlation analysis enabled a first portray of the interaction occurring between the root host transcriptome and the endophytic community. To further identify keystone operational taxonomic units (OTUs) and genes, subsequent co-occurrence network analysis showed significant interactions between 32 differentially expressed genes (DEGs) and 19 OTUs. Overall, negative correlation was detected between all upregulated genes in the AH group and all OTUs except of Actinophytocola. While two groups of olive cultivars grown under the same conditions showed significantly different microbial profiles, the most remarkable finding was to unveil a strong correlation between these profiles and the differential gene expression pattern of each group. In conclusion, this study shows a holistic view of the plant-microbiome communication.

Applications of Microsatellite Markers for the Characterization of Olive Genetic Resources of Tunisia

Among the countries of the Mediterranean Basin, Tunisia is located at the crossroad for the immigration of several civilizations over the last two millennia, becoming a strategic place for gene flow, and a secondary center of diversity for olive species. Olive is one of the principal crop species in Tunisia and now it strongly characterizes the rural landscape of the country. In recent years, collecting missions on farm and in situ were carried out by various institutes, with special emphasis given to ex situ collections serving as a reference for the identification of olive germplasm. Simple Sequence Repeats (SSRs) represent the easiest and cheapest markers for olive genetic fingerprinting and have been the tool of choice for studying the genetic diversity of this crop in Tunisia, to resolve cases of homonymy and synonymy among the commercialized varieties, to identify rare cultivars, to improve knowledge about the genetic variability of this crop, to identify a hot spot of olive biodiversity in the Tunisian oasis of Degache, and to enrich the national reference collection of olive varieties. The present review describes the state of the art of the genetic characterization of the Tunisian olive germplasm and illustrate the progress obtained through the SSR markers, in individuating interesting genotypes that could be used for facing incoming problems determined by climate changes.

Genetic Diversity Assessment of a Chinese Medicinal Endemic Species, Aspidopterys obcordata var. obcordata, by Combined Molecular Marker Methods (ISSR & SRAP)

Aspidopterys obcordata var. obcordata, a medicinal plant endemic to China, is a narrowly distributed species and wild resources are extremely limited. To evaluate the genetic variability and degree of genetic divergence of A. obcordata var. obcordata, and to make rational scientific decisions on its harvest and germplasm conservation, we collected 122 samples from across nearly all of its distribution area and studied genetic diversity using inter-simple sequence repeats (ISSRs), sequence-related amplified polymorphisms (SRAPs), and a method combining the two techniques. The results revealed the high genetic diversity of A. obcordata var. obcordata, mainly due to its intra-population diversity, and the top two populations with the highest levels of intra-population diversity were ML and DH, individuals of which can serve as excellent germplasm candidates during the processing of germplasm screening and conservation. In general, the combining method was prior to the ISSR analyses and SRAP analyses results, except for a slight difference in the genetic structure of individual populations. Therefore, we suggest that a combination analysis of the two marker methods is ideal for evaluating the genetic diversity and genetic relationships of A. obcordata var. obcordata.

Authentication of olive oil based on DNA analysis

Olive oil, which has been produced mainly in the Mediterranean area since the ancient times, has a high nutritional value linked to many health benefits. Extra virgin, which is the purest form of olive oil, has excellent quality and premium prices. Many cases of adulteration and fraud necessitate the development of reliable and accurate methods for olive oil authentication. DNA-based methods analyze the residual DNA extracted from olive oil and use molecular markers for genetic identification of different species, subspecies or cultivars because these markers act as signs which reflect distinct genetic profiles. This study reviews the process by which DNA from olive oil is extracted and analyzed by the most recently used markers in the authentication of olive oil, such as Simple Sequence Repeats (SSR) or microsatellites and the single nucleotide polymorphisms (SNPs). Methods of analysis such as qPCR and digital PCR are also discussed with a special emphasis placed on the method of High-Resolution Melting (HRM), a post-polymerase chain reaction method, which enables rapid, high performing identification of genetic variants in the DNA regions of interest without sequencing, and may differentiate very similar cultivars which differ in only one nucleotide in a specific locus.

Genetic Identification of the Wild Form of Olive (Olea Europaea var. Sylvestris) Using Allele-Specific Real-Time PCR

The wild-type of olive tree, Olea europaea var Sylvestris or oleaster, is the ancestor of the cultivated olive tree. Wild-type olive oil is considered to be more nutritious with increased antioxidant activity compared to the common cultivated type (Olea europaea L. var Europaea). This has led to the wild-type of olive oil having a much higher financial value. Thus, wild olive oil is one of the most susceptible agricultural food products to adulteration with other olive oils of lower nutritional and economical value. As cultivated and wild-type olives have similar phenotypes, there is a need to establish analytical methods to distinguish the two plant species. In this work, a new method has been developed which is able to distinguish Olea europaea var Sylvestris (wild-type olive) from Olea europaea L. var Europaea (cultivated olive). The method is based, for the first time, on the genotyping, by allele-specific, real-time PCR, of a single nucleotide polymorphism (SNP) present in the two olives’ chloroplastic genomes. With the proposed method, we were able to detect as little as 1% content of the wild-type olive in binary DNA mixtures of the two olive species.

The newly developed genomic-SSR markers uncover the genetic characteristics and relationships of olive accessions

Background

Olive (Olea europaea L.) is an important oil and fruit crop worldwide, owning a rich germplasm with a large number of cultivars. Simple sequence repeats (SSRs) are excellent markers and have been used for the identification of olive cultivars. However, the limited number of SSR markers and the occurrence of confusion on the names of cultivars, as well as the possible appearance of clonal variation make it difficult to identify cultivars and interpret relationships among olive cultivars.

Method

SSR markers were designed based on trinucleotide repeat sequences by screening the whole genome of olive, and the polymorphic SSR markers were developed that were applied to the identification of 53 olive accessions. The genetic characteristics and relationships of these olive accessions were evaluated based on the developed SSR markers.

Results

Twenty-one highly polymorphic genomic-SSR markers were developed, covering most chromosomes of olive. These SSR markers could well distinguish all 53 olive accessions, confirming their effectiveness. DNA fingerprints of the 53 olive accessions were constructed based on the 21 SSR markers. The dendrogram clearly divided the tested accessions into two main groups, which was also supported by the results of principal coordinate analysis. A total of 31 private alleles were detected in 15 olive accessions, which reflected the genetic diversity within 53 olive accessions to some extent. Six homonymy cases were also clarified by genetic analysis. These results suggest that the newly developed olive SSR markers are informative for the exploitation, preservation and breeding of olive.

Analysis of Microsatellites (SSRs) in Processed Olives as a Means of Cultivar Traceability and Authentication

Select cultivars of table olives have more desirable traits and a higher economic value. There are suspected issues with cultivar mislabeling and traceability in the supply chain. Here, we describe a method to identify cultivars by genotyping of processed olives. DNA was extracted from leaves and California-style olives of seven commonly packed cultivars. Processed olive fruits yielded relatively low DNA concentrations (0.04-0.86 μg/g), and extracts had more impurities compared with leaves. From 15 candidate SSRs, five markers showing the highest number of unique allele combinations and discriminatory power were selected. These SSRs were successfully amplified and analyzed in all cultivars of olives except one. When directly comparing any two cultivars, different allele combinations were typically present for at least four of the five SSRs. Microsatellite analysis shows potential as a simple yet robust diagnostic tool. The method can be expanded to include other cultivars, styles of table olives, and potentially other processed plant-based foods.

A Robust DNA Isolation Protocol from Filtered Commercial Olive Oil for PCR-Based Fingerprinting

Extra virgin olive oil (EVOO) has elevated commercial value due to its health appeal, desirable characteristics and quantitatively limited production, and thus it has become an object of intentional adulteration. As EVOOs on the market might consist of a blend of olive varieties or sometimes even of a mixture of oils from different botanical species, an array of DNA-fingerprinting methods have been developed to check the varietal composition of the blend. Starting from a comparison between publicly available DNA extraction protocols, we set up a timely, low-cost, reproducible and effective DNA isolation protocol, which allows an adequate amount of DNA to be recovered even from commercial filtered EVOOs. Then, in order to verify the effectiveness of the DNA extraction protocol herein proposed, we applied PCR-based fingerprinting methods starting from the DNA extracted from three EVOO samples of unknown composition. In particular, genomic regions harboring nine simple sequence repeats (SSRs) and eight genotyping-by-sequencing-derived single nucleotide polymorphism (SNP) markers were amplified for authentication and traceability of the three EVOO samples. The whole investigation strategy herein described might favor producers in terms of higher revenues and consumers in terms of price transparency and food safety.

Usefulness of a New Large Set of High Throughput EST-SNP Markers as a Tool for Olive Germplasm Collection Management

Germplasm collections are basic tools for conservation, characterization, and efficient use of olive genetic resources. The identification of the olive cultivars maintained in the collections is an important ongoing task which has been performed by both, morphological and molecular markers. In the present study, based on the sequencing results of previous genomic projects, a new set of 1,043 EST-SNP markers has been identified. In order to evaluate its discrimination capacity and utility in diversity studies, this set of markers was used in a representative number of accessions from 20 different olive growing countries and maintained at the World Olive Germplasm Collection of IFAPA Centre 'Alameda del Obispo' (Córdoba, Spain), one of the world's largest olive germplasm bank. Thus, the cultivated material included: cultivars belonging to previously defined core collections by means of SSR markers and agronomical traits, well known homonymy cases, possible redundancies previously identified in the collection, and recently introduced accessions. Marker stability was tested in repeated analyses of a selected number of accessions, as well as in different trees and accessions belonging to the same cultivar. In addition, 15 genotypes from a cross 'Picual' × 'Arbequina' cultivars from the IFAPA olive breeding program and a set of 89 wild genotypes were also included in the study. Our results indicate that, despite their relatively wide variability, the new set of EST-SNPs displayed lower levels of genetic diversity than SSRs in the set of olive core collections tested. However, the EST-SNP markers displayed consistent and reliable results from different plant material sources and plant propagation events. The EST-SNPs revealed a clear cut off between inter- and intra-cultivar variation in olive. Besides, they were able to reliably discriminate among different accessions, to detect possible homonymy cases as well as efficiently ascertain the presence of redundant germplasm in the collection. Additionally, these markers were highly transferable to the wild genotypes. These results, together with the low genotyping error rates and the easy and fully automated procedure used to get the genotyping data, validate the new set of EST-SNPs as possible markers of choice for olive cultivar identification.

Genetic Diversity and Genetic Relationships of Purple Willow (Salix purpurea L.) from Natural Locations

In this study, the genetic diversity and structure of 13 natural locations of Salix purpurea were determined with the use of AFLP (amplified length polymorphism), RAPD (randomly amplified polymorphic DNA) and ISSR (inter-simple sequence repeats). The genetic relationships between 91 examined S. purpurea genotypes were evaluated by analyses of molecular variance (AMOVA), principal coordinates analyses (PCoA) and UPGMA (unweighted pair group method with arithmetic mean) dendrograms for both single marker types and a combination of all marker systems. The locations were assigned to distinct regions and the analysis of AMOVA (analysis of molecular variance) revealed a high genetic diversity within locations. The genetic diversity between both regions and locations was relatively low, but typical for many woody plant species. The results noted for the analyzed marker types were generally comparable with few differences in the genetic relationships among S. purpurea locations. A combination of several marker systems could thus be ideally suited to understand genetic diversity patterns of the species. This study makes the first attempt to broaden our knowledge of the genetic parameters of the purple willow (S. purpurea) from natural location for research and several applications, inter alia breeding purposes.

Genetic Diversity and Genetic Relationships of Purple Willow (Salix purpurea L.) from Natural Locations

In this study, the genetic diversity and structure of 13 natural locations of Salix purpurea were determined with the use of AFLP (amplified length polymorphism), RAPD (randomly amplified polymorphic DNA) and ISSR (inter-simple sequence repeats). The genetic relationships between 91 examined S. purpurea genotypes were evaluated by analyses of molecular variance (AMOVA), principal coordinates analyses (PCoA) and UPGMA (unweighted pair group method with arithmetic mean) dendrograms for both single marker types and a combination of all marker systems. The locations were assigned to distinct regions and the analysis of AMOVA (analysis of molecular variance) revealed a high genetic diversity within locations. The genetic diversity between both regions and locations was relatively low, but typical for many woody plant species. The results noted for the analyzed marker types were generally comparable with few differences in the genetic relationships among S. purpurea locations. A combination of several marker systems could thus be ideally suited to understand genetic diversity patterns of the species. This study makes the first attempt to broaden our knowledge of the genetic parameters of the purple willow (S. purpurea) from natural location for research and several applications, inter alia breeding purposes.

Description of olive morphological parameters by using open access software

BACKGROUND

The morphological analysis of olive leaves, fruits and endocarps may represent an efficient tool for the characterization and discrimination of cultivars and the establishment of relationships among them. In recent years, much attention has been focused on the application of molecular markers, due to their high diagnostic efficiency and independence from environmental and phenological variables.

RESULTS

In this study, we present a semi-automatic methodology of detecting various morphological parameters. With the aid of computing and image analysis tools, we created semi-automatic algorithms applying intuitive mathematical descriptors that quantify many fruit, leaf and endocarp morphological features. In particular, we examined quantitative and qualitative characters such as size, shape, symmetry, contour roughness and presence of additional structures such as nipple, petiole, endocarp surface roughness, etc..

CONCLUSION

We illustrate the performance and the applicability of our approach on Greek olive cultivars; on sets of images from fruits, leaves and endocarps. In addition, the proposed methodology was also applied for the description of other crop species morphologies such as tomato, grapevine and pear. This allows us to describe crop morphologies efficiently and robustly in a semi-automated way.

Recent developments in olive (Olea europaea L.) genetics and genomics: applications in taxonomy, varietal identification, traceability and breeding

The latest results in DNA markers application and genomic studies in olive. Olive (Olea europaea L.) is among the most ancient tree crops worldwide and the source of oil beneficial for human health. Despite this, few data on olive genetics are available in comparison with other cultivated plant species. Molecular information is mainly linked to molecular markers and their application to the study of DNA variation in the Olea europaea complex. In terms of genomic research, efforts have been made in sequencing, heralding the era of olive genomic. The present paper represents an update of a previous review work published in this journal in 2011. The review is again mainly focused on DNA markers, whose application still constitutes a relevant percentage of the most recently published researches. Since the olive genomic era has recently started, the latest results in this field are also being discussed.

Elucidate genetic diversity and population structure of Olea europaea L. germplasm in Iran using AFLP and IRAP molecular markers

Currently, study of the inter and the intra-population genetic disparity was done by use of the 200 Olea europaea L. which is found growing naturally in the nation of Iran, and this study was carried out by AFLP and IRAP markers. The fingerprints that were similar to the AFLP and the IRAP markers were evidence of high concentrations of heterozygosity and this shows that O. europaea L. is primarily the out crossing species. The average percentage of polymorphism is as shown below: 87.15 and 87.38% of the information used in regard to the AFLP and the IRAP, respectively. The gene disparity numerals on the population researched were 1.087 for HT and 0.871 for HS in regard to AFLP. For the IRAP it was 1.084 for HT and 0.860 for HS. The general values for genetic variations that are found in the O. europaea L. germplasm in the nation of Iran were then assessed through putting together the AFLP and the IRAP information so as to cover a larger genome. Arguing from the AFLP and the IRAP studies, it can be concluded that there are more levels of genetic variation at inter and the intra-population level for the O. europaea.

The First Molecular Identification of an Olive Collection Applying Standard Simple Sequence Repeats and Novel Expressed Sequence Tag Markers

Germplasm collections of tree crop species represent fundamental tools for conservation of diversity and key steps for its characterization and evaluation. For the olive tree, several collections were created all over the world, but only few of them have been fully characterized and molecularly identified. The olive collection of Perugia University (UNIPG), established in the years' 60, represents one of the first attempts to gather and safeguard olive diversity, keeping together cultivars from different countries. In the present study, a set of 370 olive trees previously uncharacterized was screened with 10 standard simple sequence repeats (SSRs) and nine new EST-SSR markers, to correctly and thoroughly identify all genotypes, verify their representativeness of the entire cultivated olive variation, and validate the effectiveness of new markers in comparison to standard genotyping tools. The SSR analysis revealed the presence of 59 genotypes, corresponding to 72 well known cultivars, 13 of them resulting exclusively present in this collection. The new EST-SSRs have shown values of diversity parameters quite similar to those of best standard SSRs. When compared to hundreds of Mediterranean cultivars, the UNIPG olive accessions were splitted into the three main populations (East, Center and West Mediterranean), confirming that the collection has a good representativeness of the entire olive variability. Furthermore, Bayesian analysis, performed on the 59 genotypes of the collection by the use of both sets of markers, have demonstrated their splitting into four clusters, with a well balanced membership obtained by EST respect to standard SSRs. The new OLEST (Olea expressed sequence tags) SSR markers resulted as effective as the best standard markers. The information obtained from this study represents a high valuable tool for ex situ conservation and management of olive genetic resources, useful to build a common database from worldwide olive cultivar collections, also based on recently developed markers.

Evolution and perspectives of cultivar identification and traceability from tree to oil and table olives by means of DNA markers

In recent years, an increasing number of typicality marks has been awarded to high-quality olive oils produced from local cultivars. In this case, quality control requires effective varietal checks of the starting materials. Moreover, accurate cultivar identification is essential in vegetative-propagated plants distributed by nurseries and is a pre-requisite to register new cultivars. Food genomics provides many tools for cultivar identification and traceability from tree to oil and table olives. The results of the application of different classes of DNA markers to olive with the purpose of checking cultivar identity and variability of plant material are extensively discussed in this review, with special regard to repeatability issues and polymorphism degree. The characterization of olive germplasm from all countries of the Mediterranean basin and from less studied geographical areas is described and innovative high-throughput molecular tools to manage reference collections are reviewed. Then the transferability of DNA markers to processed products - virgin olive oils and table olives - is overviewed to point out strengths and weaknesses, with special regard to (i) the influence of processing steps and storage time on the quantity and quality of residual DNA, (ii) recent advances to overcome the bottleneck of DNA extraction from processed products, (iii) factors affecting whole comparability of DNA profiles between fresh plant materials and end-products, (iv) drawbacks in the analysis of multi-cultivar versus single-cultivar end-products and (v) the potential of quantitative polymerase chain reaction (PCR)-based techniques. © 2016 Society of Chemical Industry.

Genetic improvement of olive (Olea europaea L.) by conventional and in vitro biotechnology methods

In olive (Olea europaea L.) traditional methods of genetic improvement have up to now produced limited results. Intensification of olive growing requires appropriate new cultivars for fully mechanized groves, but among the large number of the traditional varieties very few are suitable. High-density and super high-density hedge row orchards require genotypes with reduced size, reduced apical dominance, a semi-erect growth habit, easy to propagate, resistant to abiotic and biotic stresses, with reliably high productivity and quality of both fruits and oil. Innovative strategies supported by molecular and biotechnological techniques are required to speed up novel hybridisation methods. Among traditional approaches the Gene Pool Method seems a reasonable option, but it requires availability of widely diverse germplasm from both cultivated and wild genotypes, supported by a detailed knowledge of their genetic relationships. The practice of "gene therapy" for the most important existing cultivars, combined with conventional methods, could accelerate achievement of the main goals, but efforts to overcome some technical and ideological obstacles are needed. The present review describes the benefits that olive and its products may obtain from genetic improvement using state of the art of conventional and unconventional methods, and includes progress made in the field of in vitro techniques. The uses of both traditional and modern technologies are discussed with recommendations.

Olive oil DNA fingerprinting by multiplex SNP genotyping on fluorescent microspheres

Olive oil cultivar verification is of primary importance for the competitiveness of the product and the protection of consumers and producers from fraudulence. Single-nucleotide polymorphisms (SNPs) have emerged as excellent DNA markers for authenticity testing. This paper reports the first multiplex SNP genotyping assay for olive oil cultivar identification that is performed on a suspension of fluorescence-encoded microspheres. Up to 100 sets of microspheres, with unique "fluorescence signatures", are available. Allele discrimination was accomplished by primer extension reaction. The reaction products were captured via hybridization on the microspheres and analyzed, within seconds, by a flow cytometer. The "fluorescence signature" of each microsphere is assigned to a specific allele, whereas the signal from a reporter fluorophore denotes the presence of the allele. As a model, a panel of three SNPs was chosen that enabled identification of five common Greek olive cultivars (Adramytini, Chondrolia Chalkidikis, Kalamon, Koroneiki, and Valanolia).

Traditional Uses, Phytochemistry, and Pharmacology of Olea europaea (Olive)

Aim of the Review. To grasp the fragmented information available on the botany, traditional uses, phytochemistry, pharmacology, and toxicology of Olea europaea to explore its therapeutic potential and future research opportunities. Material and Methods. All the available information on O. europaea was collected via electronic search (using Pubmed, Scirus, Google Scholar, and Web of Science) and a library search. Results. Ethnomedical uses of O. europaea are recorded throughout the world where it has been used to treat various ailments. Phytochemical research had led to the isolation of flavonoids, secoiridoids, iridoids, flavanones, biophenols, triterpenes, benzoic acid derivatives, isochromans, and other classes of secondary metabolites from O. europaea. The plant materials and isolated components have shown a wide spectrum of in vitro and in vivo pharmacological activities like antidiabetic, anticonvulsant, antioxidant, anti-inflammatory, immunomodulatory, analgesic, antimicrobial, antiviral, antihypertensive, anticancer, antihyperglycemic, antinociceptive, gastroprotective, and wound healing activities. Conclusions. O. europaea emerged as a good source of traditional medicine for the treatment of various ailments. The outcomes of phytochemical and pharmacological studies reported in this review will further expand its existing therapeutic potential and provide a convincing support to its future clinical use in modern medicine.

SNP discovery by illumina-based transcriptome sequencing of the olive and the genetic characterization of Turkish olive genotypes revealed by AFLP, SSR and SNP markers

Background

The olive tree (Olea europaea L.) is a diploid (2n = 2x = 46) outcrossing species mainly grown in the Mediterranean area, where it is the most important oil-producing crop. Because of its economic, cultural and ecological importance, various DNA markers have been used in the olive to characterize and elucidate homonyms, synonyms and unknown accessions. However, a comprehensive characterization and a full sequence of its transcriptome are unavailable, leading to the importance of an efficient large-scale single nucleotide polymorphism (SNP) discovery in olive. The objectives of this study were (1) to discover olive SNPs using next-generation sequencing and to identify SNP primers for cultivar identification and (2) to characterize 96 olive genotypes originating from different regions of Turkey.

Methodology/Principal Findings

Next-generation sequencing technology was used with five distinct olive genotypes and generated cDNA, producing 126,542,413 reads using an Illumina Genome Analyzer IIx. Following quality and size trimming, the high-quality reads were assembled into 22,052 contigs with an average length of 1,321 bases and 45 singletons. The SNPs were filtered and 2,987 high-quality putative SNP primers were identified. The assembled sequences and singletons were subjected to BLAST similarity searches and annotated with a Gene Ontology identifier. To identify the 96 olive genotypes, these SNP primers were applied to the genotypes in combination with amplified fragment length polymorphism (AFLP) and simple sequence repeats (SSR) markers.

Conclusions/Significance

This study marks the highest number of SNP markers discovered to date from olive genotypes using transcriptome sequencing. The developed SNP markers will provide a useful source for molecular genetic studies, such as genetic diversity and characterization, high density quantitative trait locus (QTL) analysis, association mapping and map-based gene cloning in the olive. High levels of genetic variation among Turkish olive genotypes revealed by SNPs, AFLPs and SSRs allowed us to characterize the Turkish olive genotype.

De novo assembly and functional annotation of the olive (Olea europaea) transcriptome

Olive breeding programmes are focused on selecting for traits as short juvenile period, plant architecture suited for mechanical harvest, or oil characteristics, including fatty acid composition, phenolic, and volatile compounds to suit new markets. Understanding the molecular basis of these characteristics and improving the efficiency of such breeding programmes require the development of genomic information and tools. However, despite its economic relevance, genomic information on olive or closely related species is still scarce. We have applied Sanger and 454 pyrosequencing technologies to generate close to 2 million reads from 12 cDNA libraries obtained from the Picual, Arbequina, and Lechin de Sevilla cultivars and seedlings from a segregating progeny of a Picual × Arbequina cross. The libraries include fruit mesocarp and seeds at three relevant developmental stages, young stems and leaves, active juvenile and adult buds as well as dormant buds, and juvenile and adult roots. The reads were assembled by library or tissue and then assembled together into 81 020 unigenes with an average size of 496 bases. Here, we report their assembly and their functional annotation.

Involvement of alternative oxidase (AOX) in adventitious rooting of Olea europaea L. microshoots is linked to adaptive phenylpropanoid and lignin metabolism

Alternative oxidase (AOX) has been proposed as a functional marker candidate in a number of events involving cell differentiation, including rooting efficiency in semi-hardwood shoot cuttings of olive (Olea europaea L.). To ascertain the general importance of AOX in olive rooting, the auxin-induced rooting process was studied in an in vitro system for microshoot propagation. Inhibition of AOX by salicylhydroxamic acid (SHAM) significantly reduced rooting efficiency. However, the inhibitor failed to exhibit any effect on the preceding calli stage. This makes the system appropriate for distinguishing dedifferentiation and de novo differentiation during root induction. Metabolite analyses of microshoots showed that total phenolics, total flavonoids and lignin contents were significantly reduced upon SHAM treatment. It was concluded that the influence of alternative respiration on root formation was associated to adaptive phenylpropanoid and lignin metabolism. Transcript profiles of two olive AOX genes (OeAOX1a and OeAOX2) were examined during the process of auxin-induced root induction. Both genes displayed stable transcript accumulation in semi-quantitative RT-PCR analysis during all experimental stages. In contrary, when the reverse primer for OeAOX2 was designed from the 3'-UTR instead of the ORF, differential transcript accumulation was observed suggesting posttranscriptional regulation of OeAOX2 during metabolic acclimation. This result confirms former observations in olive semi-hardwood shoot cuttings on differential OeAOX2 expression during root induction. It further points to the importance of future studies on the functional role of sequence and length polymorphisms in the 3'-UTR of this gene.

KEY MESSAGE

The manuscript reports the general importance of AOX in olive adventitious rooting and the association of alternative respiration to adaptive phenylpropanoid and lignin metabolism.

Comparative transcriptome analysis of two olive cultivars in response to NaCl-stress

BACKGROUND

Olive (Olea europaea L.) cultivation is rapidly expanding and low quality saline water is often used for irrigation. The molecular basis of salt tolerance in olive, though, has not yet been investigated at a system level. In this study a comparative transcriptomics approach was used as a tool to unravel gene regulatory networks underlying salinity response in olive trees by simulating as much as possible olive growing conditions in the field. Specifically, we investigated the genotype-dependent differences in the transcriptome response of two olive cultivars, a salt-tolerant and a salt-sensitive one.

METHODOLOGY/PRINCIPAL FINDINGS

A 135-day long salinity experiment was conducted using one-year old trees exposed to NaCl stress for 90 days followed by 45 days of post-stress period during the summer. A cDNA library made of olive seedling mRNAs was sequenced and an olive microarray was constructed. Total RNA was extracted from root samples after 15, 45 and 90 days of NaCl-treatment as well as after 15 and 45 days of post-treatment period and used for microarray hybridizations. SAM analysis between the NaCl-stress and the post-stress time course resulted in the identification of 209 and 36 differentially expressed transcripts in the salt-tolerant and salt-sensitive cultivar, respectively. Hierarchical clustering revealed two major, distinct clusters for each cultivar. Despite the limited number of probe sets, transcriptional regulatory networks were constructed for both cultivars while several hierarchically-clustered interacting transcription factor regulators such as JERF and bZIP homologues were identified.

CONCLUSIONS/SIGNIFICANCE

A systems biology approach was used and differentially expressed transcripts as well as regulatory interactions were identified. The comparison of the interactions among transcription factors in olive with those reported for Arabidopsis might indicate similarities in the response of a tree species with Arabidopsis at the transcriptional level under salinity stress.

Morphological traits and RAPD markers for characterization and identification of minor Spanish olive cultivars from the Extremadura region

A total of 91 wild olive accessions and 31 olive cultivars growing in the Extremadura region of central-western Spain were analyzed using morphological traits and RAPD markers. We focused on three main and 16 minor Spanish olive cultivars that are recognized as native or local to the Extremadura region. The five arbitrary 10-mer primers tested on the olive cultivars gave 67 polymorphic bands, representing 91% of the total amplification products. The number of bands per primer ranged from 9 to 18, whereas the number of polymorphic bands ranged from 8 to 17. All the cultivars could be identified by a combination of three primers (OPF-6, OPA-8, and OPK-16); four cultivar-specific markers were detected. The minor local "Jariego" and "Tempranillo" cultivars showed the most distal similarities. The resulting dendrogram, using the unweighted pair-group method with arithmetic mean clustering algorithm, depicted the pattern of relationships between the local Extremadura cultivars and the cultivars from geographically connected regions. This analysis showed a correlation between most of the minor local cultivars and the geographical origin; there was no apparent clustering according to morphological traits or fruit use of olive cultivars when these parameters were used as analysis criteria.

Selective recognition of DNA from olive leaves and olive oil by PNA and modified-PNA microarrays

PNA probes for the specific detection of DNA from olive oil samples by microarray technology were developed. The presence of as low as 5% refined hazelnut (Corylus avellana) oil in extra-virgin olive oil (Olea europaea L.) could be detected by using a PNA microarray. A set of two single nucleotide polymorphisms (SNPs) from the Actin gene of Olive was chosen as a model for evaluating the ability of PNA probes for discriminating olive cultivars. Both unmodified and C2-modified PNAs bearing an arginine side-chain were used, the latter showing higher sequence specificity. DNA extracted from leaves of three different cultivars (Ogliarola leccese, Canino and Frantoio) could be easily discriminated using a microarray with unmodified PNA probes, whereas discrimination of DNA from oil samples was more challenging, and could be obtained only by using chiral PNA probes.