4
Cytogenetics, Epigenetics
and Karyotype Evolution
of Duckweeds
Xuan Hieu Cao and Giang T. H. Vu
Abstract
Duckweed is an interesting model for studying cytogenetics, epigenetics and karyotype
evolution. Belonging to the monocotyledonous arum or aroid family Araceae, these
aquatic plants present an approximately
12-fold range of different genome sizes, from
158 Mbp (Spirodela sps.) to 1881 Mbp
(Wolffia arrhiza) and variable chromosome
numbers. In addition to reduced gene repertoires that found in so far all published
duckweed genomes of Spirodela, Lemna and
Wolffia species, several peculiar genome and
epigenome features (e.g. the lowest copy
number of genes coding for rRNA, extreme
levels of global DNA methylation, and atypical patterns of heterochromatic and euchromatic territories) indicate a unique and
interesting history of duckweed genome evolution, organization and adaptation to plants
with simplified body architecture and
extremely fast growth rate. Together with the
high-throughput
long-read,
long-range
information and optical mapping technologies, available cytogenetic resources, including an efficient and robust protocol of
multicolour fluorescence in situ hybridization
(mcFISH) and mitotic chromosome preparation, and a Spirodela genome-integrated
bacterial-artificial-chromosome (BAC) map
with ancestral chromosome linkages allow
further comprehensive comparative genomic
and cytogenetic analysis between duckweed,
its close relatives, and other monocotyledonous plants of interest.
4.1 Introduction
Duckweeds are very small, free-floating aquatic
plants that most people can easily and morphologically distinguish from species of any other
flowering plants, even closely related aquatic
plants, due to their simplified body structure.
Morphological traits and molecular data both
support a placement of duckweeds as an early
and monophyletic branch of the arum or aroid
family Araceae (Cabrera et al. 2008; Cusimano
et al. 2011; Nauheimer et al. 2012; Henriquez
et al. 2014). Duckweeds were first described as a
family, the Lemnaceae, by S. F. Gray in 1821
(Gray 1821). In contrast, Engler (1876) in his
early works on aroids classified the duckweeds as
a subfamily of Araceae under the name
Lemnoideae. However, later he considered
X. H. Cao (&)
Institute of Biology/Plant Physiology, Martin-Luther
University of Halle-Wittenberg, Weinbergweg 10,
06120 Halle, Germany
e-mail: xuan.cao@biologie.uni-halle.de
G. T. H. Vu
Leibniz Institute of Plant Genetics and Crop Plant
Research (IPK), Corrensstrasse 3, 06166
Gatersleben, Germany
© Springer Nature Switzerland AG 2020
X. H. Cao et al. (eds.), The Duckweed Genomes, Compendium of Plant Genomes,
https://doi.org/10.1007/978-3-030-11045-1_4
47
Cytogenetics, Epigenetics
and Karyotype Evolution
of Duckweeds
Xuan Hieu Cao and Giang T. H. Vu
Abstract
Duckweed is an interesting model for studying cytogenetics, epigenetics and karyotype
evolution. Belonging to the monocotyledonous arum or aroid family Araceae, these
aquatic plants present an approximately
12-fold range of different genome sizes, from
158 Mbp (Spirodela sps.) to 1881 Mbp
(Wolffia arrhiza) and variable chromosome
numbers. In addition to reduced gene repertoires that found in so far all published
duckweed genomes of Spirodela, Lemna and
Wolffia species, several peculiar genome and
epigenome features (e.g. the lowest copy
number of genes coding for rRNA, extreme
levels of global DNA methylation, and atypical patterns of heterochromatic and euchromatic territories) indicate a unique and
interesting history of duckweed genome evolution, organization and adaptation to plants
with simplified body architecture and
extremely fast growth rate. Together with the
high-throughput
long-read,
long-range
information and optical mapping technologies, available cytogenetic resources, including an efficient and robust protocol of
multicolour fluorescence in situ hybridization
(mcFISH) and mitotic chromosome preparation, and a Spirodela genome-integrated
bacterial-artificial-chromosome (BAC) map
with ancestral chromosome linkages allow
further comprehensive comparative genomic
and cytogenetic analysis between duckweed,
its close relatives, and other monocotyledonous plants of interest.
4.1 Introduction
Duckweeds are very small, free-floating aquatic
plants that most people can easily and morphologically distinguish from species of any other
flowering plants, even closely related aquatic
plants, due to their simplified body structure.
Morphological traits and molecular data both
support a placement of duckweeds as an early
and monophyletic branch of the arum or aroid
family Araceae (Cabrera et al. 2008; Cusimano
et al. 2011; Nauheimer et al. 2012; Henriquez
et al. 2014). Duckweeds were first described as a
family, the Lemnaceae, by S. F. Gray in 1821
(Gray 1821). In contrast, Engler (1876) in his
early works on aroids classified the duckweeds as
a subfamily of Araceae under the name
Lemnoideae. However, later he considered
X. H. Cao (&)
Institute of Biology/Plant Physiology, Martin-Luther
University of Halle-Wittenberg, Weinbergweg 10,
06120 Halle, Germany
e-mail: xuan.cao@biologie.uni-halle.de
G. T. H. Vu
Leibniz Institute of Plant Genetics and Crop Plant
Research (IPK), Corrensstrasse 3, 06166
Gatersleben, Germany
© Springer Nature Switzerland AG 2020
X. H. Cao et al. (eds.), The Duckweed Genomes, Compendium of Plant Genomes,
https://doi.org/10.1007/978-3-030-11045-1_4
47