Chlamydomonas chloroplasts can use short dispersed repeats and multiple pathways to repair a double-strand break in the genome

Obed W. Odom, Kwang Hyun Baek, Radhika N. Dani, David L. Herrin

Research output: Contribution to journalArticlepeer-review

16 Scopus citations


Certain group I introns insert into intronless DNA via an endonuclease that creates a double-strand break (DSB). There are two models for intron homing in phage: synthesis-dependent strand annealing (SDSA) and double-strand break repair (DSBR). The Cr.psbA4 intron homes efficiently from a plasmid into the chloroplast psbA gene in Chlamydomonas, but little is known about the mechanism. Analysis of co-transformants selected using a spectinomycin-resistant 16S gene (16Sspec) provided evidence for both pathways. We also examined the consequences of the donor DNA having only one-sided or no homology with the psbA gene. When there was no homology with the donor DNA, deletions of up to 5 kb involving direct repeats that flank the psbA gene were obtained. Remarkably, repeats as short as 15 bp were used for this repair, which is consistent with the single-strand annealing (SSA) pathway. When the donor had one-sided homology, the DSB in most co-transformants was repaired using two DNAs, the donor and the 16Sspec plasmid, which, coincidentally, contained a region that is repeated upstream of psbA. DSB repair using two separate DNAs provides further evidence for the SDSA pathway. These data show that the chloroplast can repair a DSB using short dispersed repeats located proximally, distally, or even on separate molecules relative to the DSB. They also provide a rationale for the extensive repertoire of repeated sequences in this genome.

Original languageEnglish (US)
Pages (from-to)842-853
Number of pages12
JournalPlant Journal
Issue number5
StatePublished - Mar 2008


  • Chloroplast DNA
  • DNA repair
  • Double-strand break
  • Intron homing
  • SDSA
  • SSA

ASJC Scopus subject areas

  • Genetics
  • Plant Science
  • Cell Biology


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