algal evolution johanna weston keeling, 2004. 3.5 billion cyanobacteria 2.2 to 1.5 billion...
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Algal EvolutionJohanna Weston
Keeling, 2004
• 3.5 billion cyanobacteria
• 2.2 to 1.5 billion mitochondial origin
• 1.5 – 1.2 Plastid• “Little Green
Slaves”
(Dyall et al., 2004)
ENDOSYMBIOSIS– Primary– Secondary– Tertiary– Serial Secondary
(Keeling, 2004)
How do endosymbionts become organelles?
• Organelle – discrete subcellular structure of specialized function usually bound by two or more membranes
• Metabolite antiporters and Biochemical pathways
• Genetic integration and reduction• Protein import apparatus
Phosphate Translocator Family
• Antiport dependent on counter-exchange
• Algae profit from cyanobacteria carbon fixation
• ER/Golgi metabolite translocator protein in host recruited to the plastid envelope
(Bhattacharya et al., 2007)
Transfer and Reduction
• Cyanobacteria – 2000 to 4000 kb
• Plastids– < 200 kb– < 200 genes
• “Muller’s ratchet”• Oxygen free radials
(Bhattacharya et al., 2007)
TIC - TOC
• Defining feature of organelle genesis
• Sophisticated outcome of the requirement for regulated protein import
• Evolutionary diverse origins– Cyanobacteria– Co-option of host genes– HGT from bacteria
Transit peptideNC
(Gould et al., 2008)
TIC-TOC Independent
• Existing endomembrane system of host cell
• Paulinella chromatophora
• α – carbonic anhydrase• **2o Endosymbiosis
combination of both
(Gould et al., 2008)(Bhattacharya et al., 2007)
Animal-Algal Endosymbiosis
• Elysia chlorotica and chloroplasts of Vaucheria litorea
• 9 months with only light and CO2
• Not inherited
(Mujer et al., 1996) (Green et al., 2000)
References• Bhattacharya, Debashish, et al. "How do endosymbionts become organelles? Understanding
early events in plastid evolution." BioEssay (2007): 1239-1246.• Gould, Sven, Ross Waller and Geoffrey Macfadden. "Plastid evolution." Annual Review of
Plant Biology (2008): 491-517.• Graham, Linda E., James M. Graham and Lee W. Wilcox. Algae. 2. San Francisco: Benjamin
Cummings, 2009.• Green, Brian, et al. "Mullusc-algal chloroplast endosymbiosis. Photosynthesis, thylakoid protein
maintenance, and chloroplast gene expression continue for many months in the absence of the algal nucleus." Plant Physiology (2000): 331-342.
• Keeling, Patrick. "Diversity and evolutionary history of plastids and their hosts." Americal Journal of Botany (2004): 1418-1493.
• Mujer, Cesar, et al. "Chloroplast genes are expressed during intracellular symbiotic association of Vaucheria litorea plastids with the sea slug Elysia chlorotica." Cell Biology (1996): 12333-12338.
• Weber, Andreas, Marc Linka and Debashish Bhattacharya. "Single, ancient orgin of a plastid metabolite translocator family in Plantae from an endomembrane-derived ancestor." Eukaryotic Cell (2006): 609-612.
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