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Parasitic Flowering Plants of Genus Orobanche:
DNA Markers, Molecular Evolution, and
Physiological Relations with the Host Plants
Ivan N. Minkov and Antoaneta Ljubenova*
University of Plovdiv, Plovdiv, Bulgaria
789I. INTRODUCTION
Interactions between different living organisms are a rule rather than an exception. These interactions are
called symbiosis when the species engaged live permanently together and are bound by nutritional links.
The symbiosis is mutualistic when both organisms benefit from the relationship and parasitic when only
one of the partners uses the resources of the system, thus damaging the development of the other one [1].
In ancient Greek the word parasitosmeans one who eats at the table of another. Parasitism is usu-
ally associated with insects, fungi, and microorganisms, but it also occurs among flowering plants. Al-
though parasitic plants were first mentioned as botanical curiosities [2], about 4000 species in 22 dicot
families are currently recognized as parasitic [3]. They can be placed into 11 independent phylogenetic
clades, indicating that parasitism originated several times during the evolution of angiosperms [3].
Parasitic plants represent an extraordinary adaptation in which modified roots, haustoria, are used to
transfer water, minerals and a diverse collection of carbon compounds from a host plant to the parasite [4–9].
Evolution has associated the parasitic life cycle with profound morphological, physiological, and bio-
chemical changes [1,10–19]. On several occasions this has proceeded to an extreme form known as holopara-
sitism [18,19], in which the parasite obtains virtually all of its reduced carbon from the host. In addition to the
loss of photosynthesis and associated pigments [20], holoparasites exhibit reduction or loss of leaves and loss
of nonhaustorial roots, and in one extreme group, Rafflesiaceae [21], vegetative tissues have been reduced to
a mycelium-like mass of feeding cells that reside solely within the photosynthetic host plant. There are also
hemiparasites, which contain chlorophyll but in which the photosynthetic efficiency is reduced [22–24].
The molecular mechanisms of the expression of genetic material of parasitic plants are not well un-
derstood, although they can provide valuable evidence for the evolution of flowering plants as well as for
the nature of metabolism during the parasite-host interaction. This review is focused on root parasites
from the genus Orobanche, belonging to Orobanchaceae, closely related to Scrophulariaceae. We will
discuss three areas of plant parasitism: the use of DNA molecular markers in solving taxonomy problems
within the genus; the evolutionary fate of the parasitic plant genome, especially the plastome and chon-
driome and its phylogenetic consequences; and the physiologic relations between different species of
hosts and parasites.
*Current affiliation:University of the North, Sovenga, South Africa