[PhD Thesis Presentation] ‐Girish Beedessee‐ Genomic insights on secondary metabolism in symbiotic dinoflagellates

ABSTRACT:

Dinoflagellates (division Pyrrhophyta, class Dinophyceae) are an important group of
phytoplankton found in a wide range of environment reflecting a remarkable diversity in form
and nutrition styles. They are typically unicellular, photosynthetic, free-swimming and form
part of freshwater, brackish and marine phytoplankton communities. Dinoflagellates also
produce a wide variety of secondary metabolites including toxins that are dangerous to man,
marine animals, fish and other member of food chains. At present, the only available genomes
of dinoflagellates are that of the family Symbiodiniaceae. Decoding higher order
dinoflagellates remains a challenge because of their large nuclear genomes (up to 250 Gbp).
Dinoflagellates highlight the extent of divergence that has taken place in the evolution of
eukaryotic life. Taking together the economical, ecological and evolutionary importance of
dinoflagellates, undertaking their genome sequencing is a valuable venture. For these reasons,
this dissertation aims at understanding how the chemical diversity arises in the family
Symbiodiniaceae and explain what evolutionary drivers contribute to this diversity. Next, I
decode the genome of a basal dinoflagellate, Amphidinium gibossum, known to produce
interesting small molecules of biological importance. The purpose of this new genome was to
investigate if A. gibossum secondary metabolism differs from that of the family
Symbiodiniaceae. I found that the underlying chemistry is similar, and I attempt to explain how
specialized enzymes generate unique chemical diversity in them. Lastly, I focus on how
nutrient starvation affect secondary metabolism in A. gibossum. In several dinoflagellates,
phosphate and nitrate stress are known to increase or decrease toxin production, but the
underlying transcriptomic mechanism remains limited. During such stress conditions,
expression of membrane transporters for import of specific ions is upregulated and expression
of secondary metabolism is correlated with nutrient availability, involving the action of
miRNAs.