Aretuza Sousa
Address
LMU Department für BiologieSystematische Botanik und Mykologie
Menzinger Straße 67
80638 München
Germany
Contact
| Fon: | +49 89 17861-228 |
| Fax: | +49 89 172638 |
| Email: |  |
| Room: | 25, ground floor |
Documents
Research interests
Genome evolution in the Araceae and Cucurbitaceae families
Current Ph.D. project
Testing predictions about chromosome evolution in the Araceae and Cucurbitaceae using molecular cytogenetics
From my M.Sc. thesis, I have expertise in molecular cytogenetics of plants,
including Fluorescent-in-situ-Hybridization (FISH) and other approaches that
help us understand the evolution and behavior of chromosomes. In my doctoral
research, I am using this expertise in new ways, using Araceae and Cucurbitaceae
as my systems.
One question I am addressing concerns karyotypes change during the evolution of
the ancient monocot family Araceae, which has c. 3,300 species in 117 genera. This
family presents a wide variation of chromosome number, and chromosome counts are
available for most genera. An ancestral chromosome number suggested for the family
was x = 7 (Petersen, 1989), but numbers range from
n = 4 to n = 84. Two main mechanisms are thought to explain changes
in chromosome number, polyploidy and aneuploidy, and the direction of evolutionary
change can be inferred with the help of a phylogeny. Based on the distribution of
haploid chromosome numbers and a phylogenetic tree for the Araceae, I and my
colleagues have inferred chromosome number changes in the main clades, and we found
that most likely the number of chromosomes often was reduced, not increased
(N. Cusimano, A. Sousa and S.S. Renner,
2012, Ann. Bot. online early).
Given this finding, I am now focusing on the chromosome rearrangements that led to
the inferred chromosome number reduction. To do this, I am using FISH to detect
the telomere regions, and the 5S and 45S rDNA regions in the chromosomes of
selected species of Typhonium, a genus where a hypothesized reduction
from n = 14 to n = 13. The work is ongoing (see fig. 1).
Fig. 1. Karyotype from Typhonium trilobatum with 2n = 19
after FISH experiment. Cell in a shows the chromosome set stained with
DAPI; b displays the distribution of the telomeres (green dots); c
exhibits the distribution of the 5S rDNA (red dots), and d shows the
overlapping of a, b, and c.
References
Petersen G. (1989): Cytology and systematics of Araceae. Nord. J. Bot. 9:119 – 166.
Cusimano N., A. Sousa, and S.S. Renner (2012): Maximum likelihood inference implies a high, not a low, ancestral haploid chromosome number in the Araceae, with a critique of the bias introduced by “x”. Annals of Botany 109: 681 – 692. (PDF)
Using Coccinia grandis (Cucurbitaceae) to study the evolution of sex chromosomes in plants
In this project I am focusing on the evolution of plant sex chromosomes. For this work,
I selected a species belonging to the genus Coccinia, C. grandis, which
has the largest Y chromosome known in all flowering plants (A. Souza,
N. Holstein, S.S. Renner, unpublished). Sex chromosomes are poorly known in plants,
and the only Y chromosome so far sequenced is that of the liverwort Marchantia polymorpha
(Okada et al., 2001). My study of the Coccinia grandis Y chromosome
will contribute to a better understanding of the kinds of coding and non-coding DNA that makes
up plant sex chromosomes. Right now, I am working with FISH (see fig. 2) and GISH
in this species.
Fig. 2. Karyotype from Coccinia grandis male with 2n = 24, XY
system after FISH experiment. Cell in a shows the chromosome set stained with DAPI;
b displays the distribution of 45S rDNA (green dots); c exhibits the
distribution of the 5S rDNA (red dots), and d shows the overlapping of
a, b, and c.
References
Okada S., Sone T., Fujisawa M., Nakayama S., Takenaka M., Ishizaki K., Kono K., Shimizu-Ueda Y., Hamajiri T., Yamato K.T., Fukuzawa H., Brennicke A., Ohyama K. (2001): The Y chromosome in the liverwort Marchantia polymorpha has accumulated unique repeat sequences harboring a male-specific gene. PNAS 88: 9454 – 9459.
Last update: 2012-05-15