Structural and functional characterization of genes related to the quality of plant products in olive (Olea europaea L.)
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Iaria,Domenico Lorenzo
Bitonti,Maria Beatrice
Iorio,Gabriele
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Dottorato di ricerca in Ambiente Salute e Processi Ecosostenibili, XXIII CICLO, a.a.2007-2010; Background. Olive (Olea europaea L.) is an emblematic species and one of the most
widespread fruit tree in the Mediterranean basin. It is a member of the Oleaceae family,
which includes 600 species within 25 genera distributed over all continents, from northern
temperate to southern subtropical regions and from low to high altitudes. On the basis of
several morphological synapomorphies, Oleaceae family is considered as monophyletic and
is easily circumscribed. Within the family, phylogenetic relationships among genera have
been assessed by a cladistic analysis of chloroplast non-coding DNA sequences. The different
members of Oleaceae family are trees, shrubs or woody climbers and among them Olea
europaea L. features as an evergreen schlerophyllous tree.
Native to the Mediterranean region, olive represents a unique species within the Olea
genus that produces edible fruits. There are historical evidences that the utilization of wild
olive as fruit tree can be dated to Neolithic period, as early as the 8th millennium B.C., and
that its domestic cultivation was firstly undertaken on Crete island during the Minoan period,
between 1500–3000 BC. From here, olive plants and their products were exported not only
towards mainland Greece, but also to Northern Africa and Asia Minor. Today, olive is one of
the most extensively cultivated crop species in the world and about 96% of olive cultivated
area is within the Mediterranean basin (8,6 million of hectares, over 750 million of trees).
Most of olive fruits is destined for oil production. About 73 % of the global oil production
comes from European Countries and main producers among them are Spain, Italy and Greece.
However, a considerable part of olive fruits is destined for direct human consumption as table
olives, whose worldwide production amounts to about 17 million tons.
Primarily, the quality of olive products (e.g. table olive and oil) relies on agronomic
and organoleptic features of fruits which according to botanical nomenclature are named
“drupes”. On the other hand the distinctive features of drupe vary in relation to the genetic
traits (cultivar) but also to ripening stage as well as to the environmental growth conditions
(i.e. soil and climatic conditions). Note that, these latter potentially include different biotic
and abiotic stressful factors that, besides influencing plant productivity, strongly impact on
the quality of its product. Commonly, a “good” oil (i.e. obtained from healthy drupes
collected at the optimal maturation stage) contains about 98% of acyl lipids while the
remaining 2% includes several minor component such as polyphenols, esters, terpenes,
chrorophyll, tocopherols, phylloquinones, vitamin K and unsaponifiable volatiles. The
monounsaturated oleic acid represents the main component of lipidic fraction (up to 80%).
Other major fatty acids are the polyunsaturated linoleic acid (2.5–20%) and the saturated
palmitic acid (10–20%).
Certainly, a strong impact on the perception of olive oil quality is played by sensory
testing which in turn is tightly related, on one hand to a well-balanced composition of fatty
acids and, on the other, to the profile of minor components. Chief among these components
are different volatiles responsible for characteristic aroma which make olive products unique
among other oils. Moreover, olive oil quality strongly relies on the presence of antioxidant
compounds, such as polyphenols and tocopherols, which ensures the stability of fatty acids,
acting as an effective scavenging system of reactive oxygen radicals and thus largely reducing
lipid peroxidation.
Taking into account the above features it is clear that oil extraction process is rather
relevant for preserving oil sensory properties and a high oxidative stability during storage . So
far, olive oil is the only major dietary oil extracted by pressing rather than by solvent
extraction. Therefore, no harsh treatment (high temperature, organic solvents and removal of
these by evaporation) is generally applied before olive oil is ready for human consumption.
This allows olive oil to maintain the integrity of its minor constituents, such as polyphenols,
tocopherols and volatile compounds, which are partly water-soluble and, as above mentioned,
play a key role in conferring oxidative stability and sensory properties.
It is worth noting that olive oil is a predominant and relevant component of so-called
“Mediterranean diet”. To day, a major attention is worldwide paid to this diet as a result of the
even increasing evidences of its protective action against cardiovascular diseases and cancer,
derived by both fundamental researches and epidemiological studies. Concerning olive oil,
healthy property is related to the above mentioned high proportion of monounsaturated fats as
well as to the high content of antioxidants (i.e. phenols, tocopherols, phylloquinones, vitamin
K) (Green, 2002). Consistently with this role, worldwide consumption of olive oil multiplied
6-fold over the past 30 years.
Despite the relevant properties of olive plant products, breeding strategies for this crop
species are still long term due to the long juvenile phase before flowering (20/25 years) and
the inherent self-incompatibility. Currently, olive germoplasm is under an intensive survey
but its characterisation is far from a clear definition, even though it has recently benefited by
the availability of genomic polymorphic markers. Very recently, pyrosequencing technology
provided large scale information on the structure and putative function of gene transcripts in
relation to drupe development. Notwithstanding, the information on the genetic control
underlying specific agronomic traits and/or physiological performance of olive plant is still
limited. Hence, fundamental and applied research is required to improve olive breeding
programs. In particular, a wider characterization of genes related to both the quality of plant
products and the adaptive mechanism to abiotic and biotic stresses could provide knowledge
and tools for marker aided selection (MAS) and biotechnological approach, as well as for
developing appropriate farming techniques leading to enhance productivity and quality of this
unique oil tree species.; Università della CalabriaSoggetto
Biologia vegetale; Piante oleifere; Olea europea
Relazione
BIO/04;