48 research outputs found
MRP3 is a sex determining gene in the diatom Pseudo-nitzschia multistriata
A broad diversity of sex-determining systems has evolved in eukaryotes. However, information on the mechanisms of sex determination for unicellular microalgae is limited, including for diatoms, key-players of ocean food webs. Here we report the identification of a mating type (MT) determining gene for the diatom Pseudo-nitzschia multistriata. By comparing the expression profile of the two MTs, we find five MT-biased genes, of which one, MRP3, is expressed exclusively in MT+ strains in a monoallelic manner. A short tandem repeat of specific length in the region upstream of MRP3 is consistently present in MT+ and absent in MT- strains. MRP3 overexpression in an MT- strain induces sex reversal: the transgenic MT- can mate with another MT- strain and displays altered regulation of the other MT-biased genes, indicating that they lie downstream. Our data show that a relatively simple genetic program is involved in defining the MT in P. multistriata
Taxonomy and Biogeography of the Diatom Genus Cocconeis EHR. Associated to the Seagrass Posidonia oceanica (L.) Delile in the Mediterranean Sea.
TAXONOMY AND BIOGEOGRAPHY OF THE DIATOM GENUS COCCONEIS EHR. ASSOCIATED TO THE SEAGRASS POSIDONIA OCEANICA (L.) DELILE IN THE MEDITERRANEAN SEA
Posidonia oceanica is a marine phanerogam endemic of the Mediterranean
Sea, where it produces dense matte on sandy bottoms with unsteady
hydrodynamic conditions, from shallow waters to 40 meters depth. Posidonia
oceanica leaves represent an optimal surface of colonization for a complex
epiphytic community encompassing both macroalgal and microalgal species.
Epiphytic microalgae on P. oceanica are mainly represented by pennate
diatoms. Differences in the geographic distribution of the host plant act
mainly on the species composition of the epiphytic diatom community.
Indeed, in term of functional classes or growth forms, this community seems
to be represented by a well-circumscribed group of diatom genera that can
be considered adapted to the epiphytic life-habitus. Several genera belonging
to monoraphid (e.g Cocconeis, Achnanthes, Campyloneis) and araphid (e.g
Licmophora, Synedra, Fragilaria) diatoms represent the primary encrusting
component of epiphytic community. To this component it is also associated a
motile, casual component more variable in terms of genera and characterized
mainly by biraphid diatoms (e.g. Mastogloia, Navicula, Amphora). Despite to
its crucial ecological role in the trophic chain, the diversity of the diatom
community epiphytic on P. oceanica leaves and on seagrasses in general is
poorly studied and greatly underestimated. Within the epiphytic diatom
community of P. oceanica, the genus Cocconeis can be considered one of the
most relevant in terms of species diversity and quantitative abundance. In
the present work, species and intraspecific taxa belonging to the genus
Cocconeis have been identified and described in 19 diatom communities
epiphytic on P. oceanica from selected Mediterranean areas. The fraction of
Cocconeis specimens within the total diatoms, their species diversity and the
relative abundance of each species have been analyzed in each sampled
locality. Furthermore, the diversity of Cocconeis assemblages in the different
Mediterranean basins have been compared in order to identified potential
biogeography pattern in the Mediterranean specie distribution