Plastids

1. Cyanobacterial origin of plastids
   1. Structural and molecular evidence
   2. Reduction of plastid genome
   3. Mechanisms of reduction
2. Primary vs. secondary endosymbioses
   1. Ultrastructual recognition of secondary endosymbiosis
   2. Molecular data confirm this, and raise new questions
3. Three lineages of primary plastids
   1. Parallel reduction in secondary plastids
   2. Taxa with secondary plastids
4. Number of primary plastid origins
   1. Chloroplast, Mitochondrial, and Nuclear data
   2. Patterns in reduction of the plastid genome
   3. Transit peptides (new Keegstra paper)
   4. The two membranes of primary plastids: two alternative hypotheses
5. The Green lineage
   1. Plastid characteristics
      1. Primary plastid surrounded by two membranes
      2. Chlorophyll a & b
      3. Accessory pigments; lutein, zeaxanthin, violaxanthin, etc.
      4. Thylakoids stacked in lamellae, pseudograna, or grana
      5. Do not have girdle lamellae
      6. Many have pyrenoids embedded in plastid
      7. Typically with starch deposited inside plastid
   2. Taxa
      1. Green algae and plants
      2. Chlorarachniophytes
         1. Secondary plastid, with nucleomorph and chloroplast endoplasmic reticulum (CER)
      3. Euglenoids
         1. Secondary plastid, without nucleomorph
         2. Surrounded by three membranes
         3. Do not store starch
6. The Glaucocystophyte lineage
   1. Plastid characteristics
      1. Thin peptidoglycan cell wall
      2. Chlorophyll a (not b or c)
      3. Phycobilins arranged in phycobilisomes
      4. Thylakoids are not stacked (as is the case in all taxa with phycobilisomes)
      5. DNA in single central nucleoid, polyhedral carboxysomes
      6. Food reserves as starch, stored outside of plastid
   2. Taxa
      1. Glaucocystis
      2. Bhattacharya et al. MBE 12 (1995)
      3. Paulinella
      4. Possible secondary plastid
7. The Red lineage
   1. Primary plastids in red lineage
      1. Rhodophyta
         1. Chlorophyll a only
         2. Phycobilins arranged in phycobilisomes
         3. Thylakoids are not stacked
         4. Food storage as floridean starch, stored outside of the plastid
   2. Secondary plastids in red lineage
      1. Cryptomonads
         1. Secondary plastid with nucleomorph & CER
         2. Chlorophyll a and c
         3. Phycobilins, but not arranged in phycobilisomes; rather they are in the thylakoid lumen
      2. Heterokonts
         1. Secondary plastid with CER, but no nucleomorph
         2. Chlorophylls a and c
         3. Fucoxanthin
         4. Thylakoids stacked in threes, with girdle lamellae
         5. Food storage as chrysolaminarin (beta 1,3-linked glucan), deposited outside plastid in vacuoles
         6. DNA typically in a ring-shaped nucleoid
      3. Haptophytes
         1. Secondary plastid with CER, but no nucleomorph
         2. Chlorophylls a and c
         3. Fucoxanthin
         4. Thylakoids stacked in threes, without girdle lamellae
         5. DNA in scattered nucleoids
         6. Food storage chrysolaminarin, sometimes paramylon, and formed outside plastid in vacuoles
      4. Dinoflagellates
         1. A great diversity of secondary plastids
         2. Peridinin-type plastid
            1. Chlorophyll a, c, and peridinin
            2. Surrounded by three membranes
         3. Fucoxanthin-type plastid
            1. Apparently derived from heterokonts, and probably a tertiary plastid
8. Rubisco in the red primary plastid lineage
   1. Rubisco phylogeny does not match other phylogenies
   2. Horizontal gene transfer vs. duplication
   3. Martin's view Ð metabolic redundancy
   4. Rubisco in Archaea
   5. These genes have probably not been transferred, OK as outgroup
   6. Phylogeny is not completely randomized
   7. Both duplication and transfer can be demonstrated
9. Dinoflagellate plastid diversity
   1. Lack of molecular information on peridinin-type plastids
   2. Our preliminary data
   3. Rubisco in dinoflagellate peridinin-type plastids
10. Plastids in apicomplexa
    1. Relationship between apicomplexa and dinoflagellates
    2. Comparison of hypotheses viz. homology of api and dino plastids
11. Number of secondary endosymbioses
    1. Membrane counting in taxa with secondary plastids
    2. Myzotrophy in dinoflagellates and euglenoids

Required Reading: VdH: Chapter 4; pp. 48-49; pp. 300-301.

Supplementary Reading:

Delwiche, C.F., and J.D. Palmer. 1997. The origin of plastids and their spread via secondary endosymbiosis. In D. Bhattacharya, ed., Origins of Algae and Their Plastids. Springer, New York.

Martin, W., B. Stroebe, V. Goremykin, S. Hansmann, M. Hasegawa, and K.V. Kowallik. 1998. Gene transfer to the nucleus and the evolution of chloroplasts. Nature 393:162-165.

Palmer, J.D., and C.F. Delwiche. 1996. Second-hand plastids and the case of the disappearing nucleus. Proc. Natl. Acad. Sci. USA 93:7432-7435.

Palmer, J.D., and C.F. Delwiche. 1998. The origin and evolution of plastids and their genomes. In D.E. Soltis, P.S. Soltis, and J.J. Doyle, eds., Molecular Systematics of Plants, Kluwer Academic Publishers, Boston.