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Comparative Chloroplast Genomics

Herrin, David [1], Odom, Obed [1], Corina, Laura [1].

Functional genomics of chloroplast group I introns in Chlamydomonas.

Group I (GI) introns are one of the three classes of introns found in chloroplast genomes, and are distinguished by the fact that some can self-splice in vitro and/or are mobile in vivo. GI introns are particularly common in the rRNA and psbA genes of Chlamydomonas spp., including the genetic model organism, Chlamydomonas reinhardtii, which has 4 introns in psbA (Cr.psbA1-A4), and 1 in the LSU rRNA gene (Cr.LSU). All of the C. reinhardtii introns can self-splice in vitro, but do so inefficiently at physiological temperatures. Also, efficient in vivo splicing of the psbA introns is strongly light-dependent, suggesting further that trans-acting factors facilitate splicing in vivo. Using chloroplast transformation and suppressor genetics, we have identified 3 nuclear genes that promote splicing of Cr.LSU and at least 1 psbA intron; the isolation of these genes is underway. Mobile GI (MGI) introns encode a highly specific endonuclease that cleaves intronless alleles near the intron-insertion site, thereby stimulating recombination and intron spreading. 3 of the C. reinhardtii GI introns are mobile (Cr.LSU, Cr.psbA2 and Cr.psbA4), and we have characterized the endonucleases from 2 of them. It has been suggested that mobile introns evolve from non-mobile ones by insertion of the homing endonuclease. In this regard, we note that inserting a foreign gene (aadA) into the Cr.psbA2 intron did not inhibit its splicing in vivo (although it did in vitro), and that expression of the inserted gene was quite low - both of these features make this GI intron a good home for a potentially toxic endonuclease. We are also taking advantage of cryophilic species of Chlamydomonas to examine the evolution of these GI intron ribozymes at low temperature. Finally, a database on the functional genomics of organellar introns (Fugoid) was created.


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web page for D. Herrin


1 - University of Texas at Austin, Section of Molecular Cell & Developmental Biology, 1 University Station A6700, Austin, Texas, 78712, USA

Keywords:
group I introns
psbA gene
mobile introns
self-splicing
evolution
Chlamydomonas.

Presentation Type: Symposium or Colloquium Presentation
Session: 2-4
Location: Salon K - Austin Grand Ballroom/Hilton
Date: Monday, August 15th, 2005
Time: 10:15 AM
Abstract ID:383


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