Abstract
BackgroundDinophysis is exceptional among dinoflagellates, possessing plastids derived from cryptophyte algae. Although Dinophysis can be maintained in pure culture for several months, the genus is mixotrophic and needs to feed either to acquire plastids (a process known as kleptoplastidy) or obtain growth factors necessary for plastid maintenance. Dinophysis does not feed directly on cryptophyte algae, but rather on a ciliate (Myrionecta rubra) that has consumed the cryptophytes and retained their plastids. Despite the apparent absence of cryptophyte nuclear genes required for plastid function, Dinophysis can retain cryptophyte plastids for months without feeding.ResultsTo determine if this dinoflagellate has nuclear-encoded genes for plastid function, we sequenced cDNA from Dinophysis acuminata, its ciliate prey M. rubra, and the cryptophyte source of the plastid Geminigera cryophila. We identified five proteins complete with plastid-targeting peptides encoded in the nuclear genome of D. acuminata that function in photosystem stabilization and metabolite transport. Phylogenetic analyses show that the genes are derived from multiple algal sources indicating some were acquired through horizontal gene transfer.ConclusionsThese findings suggest that D. acuminata has some functional control of its plastid, and may be able to extend the useful life of the plastid by replacing damaged transporters and protecting components of the photosystem from stress. However, the dearth of plastid-related genes compared to other fully phototrophic algae suggests that D. acuminata does not have the nuclear repertoire necessary to maintain the plastid permanently.
Highlights
Dinophysis is exceptional among dinoflagellates, possessing plastids derived from cryptophyte algae
Full-length cDNA sequences complete with the dinoflagellate-specific, trans-spliced leader motif, 5' untranslated region (UTR), and 3' UTR were obtained by PCR from D. acuminata for all five genes and used for subsequent phylogenetic analyses and targeting peptide predictions (Table 1)
We identified only one light harvesting protein (LHP) in D. acuminata, a member of the distinct LI818 LHP family involved in stabilizing the photosystem in response to heat or photodamage [3840] and may, in some situations, act as a substitute for other LHPs [39]
Summary
Dinophysis is exceptional among dinoflagellates, possessing plastids derived from cryptophyte algae. Endosymbiosis, the process through which a once freeliving organism becomes an organelle, is a major driver of eukaryotic evolution, enabling hosts to acquire novel characteristics. The primary plastids of the Archaeplastida (green, red, and glaucophyte algae) arose through an endosymbiotic relationship between a heterotrophic eukaryotic host and cyanobacteria [2]. Whereas most photosynthetic dinoflagellates have a plastid containing the photopigment peridinin, some have replaced this plastid with one acquired from haptophytes, diatoms or green algae [11]. In these organisms, the early stages of endosymbiosis have been completed and the plastids are permanent organelles
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