chromatin staining with different DNA
base-specific fluorochromes. He observed chromocenter structures, masses of heterochromatin,
by guanine-specific chromomycin A3 (CMA)
staining but not by thymine-specific 4′,6diamidino-2-phenylindole (DAPI), suggesting
the presence of GC-rich repetitive heterochromatin fractions in duckweed genomes. The more
recent investigation on nuclei of representative
duckweed species, including S. polyrhiza, La.
punctata, L. minor, W. lingulata and W. arrhiza
(Cao et al. 2015) with different sizes of genome,
found AT-rich chromocenters only in nuclei of
W. arrhiza (1C = 1881 Mbp). Interestingly, the
immunostaining, the identification of DNA
methylation (5-mC) and histone modifications
(H3K9me2 and H3K27me1) by means of
fluorescence-labelled antibodies, showed dispersed signals of those heterochromatin marks
throughout the duckweed nuclei. Such chromatin
organization, especially in small genome duckweed species, does resemble the global distribution pattern of A. thaliana nuclei particularly
from tissue culture or from young seedlings
while heterochromatin immunosignals of A.
thaliana typical nuclei are restricted to constitutive and pronounced heterochromatin chromocenters. The recent study on genome-wide
cytosine methylation of S. polyrhiza from bisulphite sequencing revealed an extremely low
global DNA methylation level (as low as 9% of
the genome, Michael et al. 2017) as compared
with A. thaliana (32%), rice (39%) or Brachypodium distachyon (54%). Given that despite an
astonishingly low genetic diversity duckweeds
demonstrate a high level of phenotypic plasticity
enabling thriving in a worldwide range of environmental conditions, this ability to adapt might
be underlined by amazingly efficient epigenetic
mechanisms including also in TE silencing
machinery (for no recent TE activity), in DNA
repair (for extremely low mutation rate) and in
transgenerational epigenetic inheritance (for the
fastest growing rate in flowering plants). In
future, detailed epigenomics and epigenetic
modifications will help researchers to delve into
exactly which (epi)genetic elements or epigenetic
pathways facilitate such high effectiveness and
efficiency in duckweed systems.
Acknowledgements We thank Charlotte Ost (University
of Halle-Wittenberg) for reading the article and for critical
discussions.
References
Appenroth KJ, Crawford DJ, Les DH (2015) After the
genome sequencing of duckweed—how to proceed
with research on the fastest growing angiosperm?
Plant Biol (Stuttg) 17:1–4. https://doi.org/10.1111/Plb.
12248
Bennett MD, Leitch IJ, Price HJ, Johnston JS (2003)
Comparisons with Caenorhabditis (approximately
100 Mb) and Drosophila (approximately 175 Mb)
using flow cytometry show genome size in Arabidopsis to be approximately 157 Mb and thus approximately 25% larger than the Arabidopsis genome
initiative estimate of approximately 125 Mb. Ann
Bot 91(5):547–557
Blackburn KB (1933) Notes on the chromosomes of the
duckweeds (Lemnaceae) introducing the question of
chromosome size. In: Proceedings of University
Durham Philosophy Society. pp 84–90
Bog M, Lautenschlager U, Landrock M, Landolt E,
Fuchs J, Sowjanya Sree K, Oberprieler C, Appenroth
K-J (2015) Genetic characterization and barcoding of
taxa in the genera Landoltia and Spirodela (Lemnaceae) by three plastidic markers and amplified
fragment length polymorphism (AFLP). Hydrobiologia 1–14. https://doi.org/10.1007/s10750-014-2163-3
Cabrera LI, Salazar GA, Chase MW, Mayo SJ, Bogner J,
Dávila P (2008) Phylogenetic relationships of aroids
and duckweeds (Araceae) inferred from coding and
noncoding plastid DNA. Am J Bot 95(9):1153–1165.
https://doi.org/10.3732/ajb.0800073
Cao HX, Vu GT, Wang W, Appenroth KJ, Messing J,
Schubert I (2016) The map-based genome sequence of
Spirodela polyrhiza aligned with its chromosomes, a
reference for karyotype evolution. New Phytol 209
(1):354–363. https://doi.org/10.1111/nph.13592
Cao HX, Vu GTH, Wang W, Messing J, Schubert I
(2015) Chromatin organisation in duckweed interphase nuclei in relation to the nuclear DNA content.
Plant Biol (Stuttg) 17:120–124. https://doi.org/10.
1111/plb.12194
Cavalier-Smith T (1985) The evolution of genome size.
Wiley Ltd, Chichester, UK
Cusimano N, Bogner J, Mayo SJ, Boyce PC, Wong SY,
Hesse M, Hetterscheid WLA, Keating RC, French JC
(2011) Relationships within the araceae: comparison
of morphological patterns with molecular phylogenies.
Am J Bot 98(4):654–668. https://doi.org/10.3732/ajb.
1000158
4 Cytogenetics, Epigenetics and Karyotype Evolution of Duckweeds
55
base-specific fluorochromes. He observed chromocenter structures, masses of heterochromatin,
by guanine-specific chromomycin A3 (CMA)
staining but not by thymine-specific 4′,6diamidino-2-phenylindole (DAPI), suggesting
the presence of GC-rich repetitive heterochromatin fractions in duckweed genomes. The more
recent investigation on nuclei of representative
duckweed species, including S. polyrhiza, La.
punctata, L. minor, W. lingulata and W. arrhiza
(Cao et al. 2015) with different sizes of genome,
found AT-rich chromocenters only in nuclei of
W. arrhiza (1C = 1881 Mbp). Interestingly, the
immunostaining, the identification of DNA
methylation (5-mC) and histone modifications
(H3K9me2 and H3K27me1) by means of
fluorescence-labelled antibodies, showed dispersed signals of those heterochromatin marks
throughout the duckweed nuclei. Such chromatin
organization, especially in small genome duckweed species, does resemble the global distribution pattern of A. thaliana nuclei particularly
from tissue culture or from young seedlings
while heterochromatin immunosignals of A.
thaliana typical nuclei are restricted to constitutive and pronounced heterochromatin chromocenters. The recent study on genome-wide
cytosine methylation of S. polyrhiza from bisulphite sequencing revealed an extremely low
global DNA methylation level (as low as 9% of
the genome, Michael et al. 2017) as compared
with A. thaliana (32%), rice (39%) or Brachypodium distachyon (54%). Given that despite an
astonishingly low genetic diversity duckweeds
demonstrate a high level of phenotypic plasticity
enabling thriving in a worldwide range of environmental conditions, this ability to adapt might
be underlined by amazingly efficient epigenetic
mechanisms including also in TE silencing
machinery (for no recent TE activity), in DNA
repair (for extremely low mutation rate) and in
transgenerational epigenetic inheritance (for the
fastest growing rate in flowering plants). In
future, detailed epigenomics and epigenetic
modifications will help researchers to delve into
exactly which (epi)genetic elements or epigenetic
pathways facilitate such high effectiveness and
efficiency in duckweed systems.
Acknowledgements We thank Charlotte Ost (University
of Halle-Wittenberg) for reading the article and for critical
discussions.
References
Appenroth KJ, Crawford DJ, Les DH (2015) After the
genome sequencing of duckweed—how to proceed
with research on the fastest growing angiosperm?
Plant Biol (Stuttg) 17:1–4. https://doi.org/10.1111/Plb.
12248
Bennett MD, Leitch IJ, Price HJ, Johnston JS (2003)
Comparisons with Caenorhabditis (approximately
100 Mb) and Drosophila (approximately 175 Mb)
using flow cytometry show genome size in Arabidopsis to be approximately 157 Mb and thus approximately 25% larger than the Arabidopsis genome
initiative estimate of approximately 125 Mb. Ann
Bot 91(5):547–557
Blackburn KB (1933) Notes on the chromosomes of the
duckweeds (Lemnaceae) introducing the question of
chromosome size. In: Proceedings of University
Durham Philosophy Society. pp 84–90
Bog M, Lautenschlager U, Landrock M, Landolt E,
Fuchs J, Sowjanya Sree K, Oberprieler C, Appenroth
K-J (2015) Genetic characterization and barcoding of
taxa in the genera Landoltia and Spirodela (Lemnaceae) by three plastidic markers and amplified
fragment length polymorphism (AFLP). Hydrobiologia 1–14. https://doi.org/10.1007/s10750-014-2163-3
Cabrera LI, Salazar GA, Chase MW, Mayo SJ, Bogner J,
Dávila P (2008) Phylogenetic relationships of aroids
and duckweeds (Araceae) inferred from coding and
noncoding plastid DNA. Am J Bot 95(9):1153–1165.
https://doi.org/10.3732/ajb.0800073
Cao HX, Vu GT, Wang W, Appenroth KJ, Messing J,
Schubert I (2016) The map-based genome sequence of
Spirodela polyrhiza aligned with its chromosomes, a
reference for karyotype evolution. New Phytol 209
(1):354–363. https://doi.org/10.1111/nph.13592
Cao HX, Vu GTH, Wang W, Messing J, Schubert I
(2015) Chromatin organisation in duckweed interphase nuclei in relation to the nuclear DNA content.
Plant Biol (Stuttg) 17:120–124. https://doi.org/10.
1111/plb.12194
Cavalier-Smith T (1985) The evolution of genome size.
Wiley Ltd, Chichester, UK
Cusimano N, Bogner J, Mayo SJ, Boyce PC, Wong SY,
Hesse M, Hetterscheid WLA, Keating RC, French JC
(2011) Relationships within the araceae: comparison
of morphological patterns with molecular phylogenies.
Am J Bot 98(4):654–668. https://doi.org/10.3732/ajb.
1000158
4 Cytogenetics, Epigenetics and Karyotype Evolution of Duckweeds
55