What type of endosymbiosis do euglenids have?
- secondary endosymbiosis with no nucleomorph and has 3 membranes
- endosymbiosis with a green alga
What evidence is there for euglenids having green algae symbionts?
- the chlorophylls used by euglenids and green algae are the same
- DNA analysis showed shared genetic sequences between euglenids and a specific clade of green algae
What evidence supports euglenids developing photosynthesis independently from other euglenophytes?
- no remnant organelles are found in the other euglenophytes to indicate the loss of a chloroplast
- other euglenophytes have genes that code for proteins that produce sugars without the need for photosynthesis
What evidence shows that cercozoans have secondary endosymbiosis?
- nucleomorph (remnant primary endosymbiont nuclei) have been found
- there are 4 membranes around the plastid, one being the phagosomal that was created when the endosymbiont was engulfed
What two groups of algae have nucleomorphs?
hacrobia and cercozoans
What did Thomas Cavalier-Smith hypothesize about SAR?
Stramenophiles and Alveolates may descend from a common ancestor with a red algae endosymbiont
What is the Chromalveolate hypothesis?
non-photosynthetic SAR members lost their plastids after the clade had developed them
How can the Chromalveolate hypothesis be studied?
study current non-photosynthetic species for evidence of a vestigial plastid, and look at similarities between photosynthetic SAR plastids
What evidence supports Apicomplexans (Alveolates) losing their plastids later on?
- some species have genes of cyanobacterial origin (gene transfer)
- some species have plastid-like organelles called apicoplasts with 4 membranes
- an Apicomplexan species was discovered still having photosynthetic abilities
What reaction is the source of bioluminescence in dinoflagelates?
the oxidation of luciferin by luciferase
What is the reaction pathway of bioluminescence?
- light is detected by the dinoflagelate and is detected as a pressure
- the pressure triggers a signal transduction where calcium ions flow into the cytoplasm
- increased calcium causes the vacuole membrane to depolarize and cause an action potential
- proton channels in scintillion organelles open
- the pH in the scintillion drops, luciferin detaches from the binding protein and attaches to luciferase, and creates light
What type of plastids are found in dinoflagellates?
peridinin from red algae (3 membranes) or kleptoplastids
How do sea slugs use photosynthesis from kleptoplastids?
- horizontal gene transfer to gain control over plastids
- plastids are stored in kleptosomes to prevent digestion
What is the hypothesis behind alveolate plastid evolution?
- common ancestor of both dinoflagellates and apicomplexans had red alga symbionts
- apicomplexans later lost plastids
- dinoflagellates later developed the peridinin plastids
What is one hypothesis for Alveolate plastid evolution?
apicomplexans, dinoflagellates and ciliates descend from a common photosynthetic ancestor
What is unique about stramenopile and hacrobian plastids?
- they have 4 membranes, the outermost is the rough ER
- they are from red algae
What are 3 hypotheses for how plastids were acquired in SAR?
- one single symbiosis event before the different groups branched off, with Rhizaria losing plastids later
- each photosynthetic group had their own symbiosis event
- the phylogenetic tree is incorrect and does not depict Rhizaria’s relationship correctly, common ancestor could have been a heterotroph
What makes oomycetes different from other stramenopiles?
- have no plastids
- have remnant phototrophic genes in their genome
What type of endosymbiosis do dinoflagellates have?
tertiary (with stramenopiles)
What type of endosymbiosis do ciliates have?
none (no plastids)
