The Robertson Lab Members

Sohini Ghoshroy, Post-doc

Research Interests

My research concerns the evolution of the gene glutamine synthetase in basal lineages of red algae. I am also interested in the evolution of this gene in select green alga and cryptophytes. Oxygenic photosynthesis is distributed among four of the five supergroups in the eukaryote tree of life. Oxygenic photosynthesis evolved within the cyanobacterial lineage and was gained by eukaryotes via primary and secondary endosymbiotic events. A number of primary and secondary endosymbiotic associations resulted in an enormous amount of genetic diversity on which natural selection could act and numerous gene duplications, replacements and losses followed the endosymbiotic events as the symbiont genomes became integrated into the genetic architecture of the host cell. Thus, the metabolic pathways that we observe today can be chimeras involving proteins encoded by genes derived from either host or endosymbiotic genomes.

Glutamine synthetase (GS) is an essential enzyme involved in nitrogen assimilation and there are three gene families (GSI, GSII, and GSIII). In many photosynthetic eukaryotes, GS isoenzymes are compartmentalized in the chloroplast and the cytosol. These isoenzymes can be members of the same family (e.g. the isoenzymes of vascular plants are members of the GSII family) or from different families (e.g. the isoenzymes of diatoms are members of the GSII and GSIII families). The GS families appear to be robust molecular markers and may be useful in unraveling the endosymbiotic histories and phylogenetic relationships among diverse lineages of organisms.

In addition to being ecologically and commercially important, rhodophytes hold a central position in endosymbiosis. Rhodophytes gained their plastid via primary endosymbiosis and contributed plastids via secondary endosymbiosis. Despite their importance, there is little information concerning the molecular evolution and regulation of nitrogen assimilation in this group. This study seeks to expand our knowledge of the distribution of GSII genes in rhodophytes, which will eventually shed light on endosymbiotic gene rearrangement events.

The lineages that arose via secondary endosymbiosis involving a red algal endosymbiont are collectively known as the chromalveolates. The chromalveolates are divided into two broad groups, chromists and alveolates. Chromists are further divided into cryptophytes, haptophytes and the heterokonts, while alveolates comprise dinoflagellates, apicomplexans and ciliates. Along with photosynthetic lineages, this broad group also includes non photosynthetic and parasitic organisms. At present, there are two major hypotheses suggesting the rise of the chromalveolate lineage. The chromalveolate hypothesis proposes that a single event of secondary endosymbiosis involving a red alga and a heterotrophic eukaryote gave rise to this lineage. The second hypothesis, one of serial endosymbiosis, which postulates that the cryptophytes were the first in line among the chromalveolate lineage to acquire the red secondary plastid and contributed it to other groups, such as the haptophyte, heterokonts and dinoflagellates in a serial manner.

The proposed research has four major goals. 1. To determine the evolution of the GSII gene within selected basal lineages of red algae using molecular and phylogenetic methods. 2. To examine the presence of isoenzymes of GSII in these red algal taxa by Southern Blot analysis, since multiple isoenzymes of GSII are common in photosynthetic eukaryotes. 3. To identify two different forms of GSII, GSII gene will be amplified from selected lineages of green algae. One of the forms is shown to be common in green algal lineages and more similar to the vascular plant GSII in evolutionary terms. The other, more rare, form has so far been identified in the green alga Chlamydomonas reinhardtii and from the genome project of the moss (bryophyte), Physcomitrella patens. 4. To shed light on the current parallel hypotheses of serial gain of secondary plastids vs. the chromalveolate hypothesis GSII gene would be amplified from the cryptophyte lineage, (Chroomonas sp. and Pyrenomonas helgolandii). The cryptophytes being the basal lineage within the chromalveolates, studying their GSII would be more informative

Education

Graduated with Ph.D. Degree in May 2011, Clark University

In 1997-2000 Sohini graduated from University of Connecticut with Master Degree in Ecology and Evolutionary Biology

In 1994-1996 Sohini graduated with Master Degree from University of Calcutta(India).

Prior to that in 1991-1994, Sohini received Bachelor Degree in zoology from University of Calcutta, Presidency College.

Publications

In preparation:

Ghoshroy, S and Deborah L. Robertson. Phylogeny of Glutamine synthetase II (GSII) genes from rhodophytes.

Ghoshroy, S and Deborah L. Robertson. Phylogeny of Glutamine synthetase II (GSII) genes from cryptophytes.

Published:

Ghoshroy, Sohini and D.L. Robertson. Molecular evolution of glutamine sythetase II and III in the chromalveolates. Journal of Phycology, Volume 48, Issue 3, pages 768– 783, June 2012.

Ghosroy, Sohini, M. Binder, A. Tartar and D. L. Robertson. Molecular evolution of glutamine synthetase II: Phylogenetic evidence of a non- endosymbiotic gene transfer event early in plant evolution. BMC Evolutionary Biology, 2010, 10:198.

Ghoshroy, S, M. Binder, A. Tartar and D. L. Robertson. Horizontal gene transfer of a Eubacterial Glutamine synthetase II gene occurred early in plant evolution. BMC Evolutionary Biology 2010, 10:198; doi:10.1186/1471-2148-10-198. http://www.biomedcentral.com/1471-2148/10/198/abstract

Ghoshroy, S. and J. N. Caira. 2001. Four new species of Acanthobothrium (Cestoda: Tetraphyllidea) from the whiptail stingray Dasyatis brevis in the Gulf of California, Mexico. Journal of Parasitology. 87(2):354-372

Ghoshroy, S. 2000. Onchobothrids from the stingrays Dasyatis brevis Garman, 1880 and Dasyatis longus Garman, 1880 in the Gulf of California, Mexico. M.S. Thesis, University of Connecticut.

Posters and Presentations:

2009 Sohini Ghoshroy, Aurelien Tartar & Deborah L. Robertson—Glutamine synthetase II: A case of lateral gene transfer in basal Viridiplantae? 48th Northeast Algal Symposium, Amherst, MA.

2006 Sohini Ghoshroy and Deborah L. Robertson. Evolutionary relationship among Rhodophytes as revealed by Glutamine Synthetase II. Evolution 2006

2006 Sohini Ghoshroy, Aurélien Tartar and Deborah L. Robertson. Unraveling the evolutionary history of glutamine synthetase II in photosynthetic lineages with an emphasis on rhodophytes. 45th Northeast Algal Symposium, Poughkeepsie, New York.

2006 Sohini Ghoshroy. Glutamine Synthetase Evolution in Rhodophytes. Graduate Student Multidisciplinary Conference, Clark University

2005 Ghoshroy, S. and D.L. Robertson. Evolution of glutamine synthetase in Rhodophytes. 44th Northeast Algal Symposium, Rockland, Maine.

2004 Robertson, D.L., S. Ghoshroy, M.L. Letsch. Glutamine synthetase gene families: An evolutionary perspective. 43rd Northeast Algal Symposium, AveryPoint, Connecticut.

1999 Ghoshroy, S., J. N. Caira and M. E. Cantino. Electron microscopy of strobilar microtriches in three species of Callliobothrium: a source of taxonomic characters. 74th Annual Meeting of the American Society of Parasitologists.

1998 Ghoshroy, S. Acanthobothrium diversity in elasmobranchs from the Gulf of California. Symposium on the metazoan parasites of elasmobranchs from the Gulf of California. 73rd Annual Meeting of the American Society of Parasitologists.

Interests

Molecular Biology, Evolution, Host parasite interactions, Phylogenomics, Molecular medicine, Functional genomics.

Resume (PDF)

Contact Info

Send Sohini an email at sghoshroy@clarku.edu