Affiliation:
1. Marine Molecular Biotechnology Laboratory, School of Oceanography, University of Washington, Seattle, Washington 98195
Abstract
ABSTRACT
Sexual reproduction is commonly assumed to occur in the vast majority of diatoms due to the intimate association of this process with cell size control. Surprisingly, however, little is known about the impact of sexual events on diatom population dynamics. The
Sig1
gene is strongly upregulated during sexual reproduction in the centric diatom
Thalassiosira weissflogii
and has been hypothesized to encode a protein involved in gamete recognition. In the present study, degenerate PCR primers were designed and used to amplify a portion of
Sig1
from three closely related species in the cosmopolitan genus
Thalassiosira,
Thalassiosira oceanica
,
Thalassiosira guillardii
, and
Thalassiosira pseudonana
. Identification of
Sig1
in these three additional species facilitated development of this gene as a molecular marker for diatom sexual events. Examination of the new sequences indicated that multiple copies of
Sig1
are probably present in the genome. Moreover, compared to the housekeeping gene
β
-tubulin
, the
Sig1
genes of isolates of
T. weissflogii
collected from different regions of the Atlantic and Pacific oceans displayed high levels of divergence. The
Sig1
genes of the four closely related
Thalassiosira
species also displayed high levels of sequence divergence compared to the levels observed with a second gene,
Fcp
, probably explaining why
Sig1
could not be amplified from more distantly related species. The high levels of sequence divergence both within and between species suggest that
Sig1
is rapidly evolving in a manner reminiscent of the manner observed in other genes that encode gamete recognition proteins. A simple model is presented for
Sig1
evolution and the implications of such a rapidly evolving sexual reproduction gene for diatom speciation and population dynamics.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
Cited by
54 articles.
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