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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