A homolog of Escherichia coli RecA protein in plastids of higher plants.

Abstract

Studies of chloroplast DNA variations, and several direct experimental observations, indicate the existence of recombination ability in algal and higher plant plastids. However, no studies have been done of the biochemical pathways involved. Using a part of a cyanobacterial recA gene as a probe in Southern blots, we have found homologous sequences in total DNA from Pisum sanvwn and Arabidopsis thaEaa and in a cDNA library from Arabidopsis. A cDNA was cloned and sequenced, and its predicted amino acid sequence Is 60.7% identical to that of the cyanobacterial RecA protein. This finding is consistent with our other results showing both DNA strand transfer activity and the existence of a protein of the predicted molecular mass crossreactive with antibodies to Escherichia coli RecA in the stroma of pea chloroplasts.The observation of chloroplast DNA recombinants in somatic hybrids of higher plants (1), genetic studies of the inheritance of chloroplast markers in several crosses of Chlamydomonas (2-4), the integration of donor DNA by homologous recombination in chloroplasts of transformed Chlamydomonas (5), and extensive comparative analyses of chloroplast genome structure (6-9) indicate that DNA recombination occurs in chloroplasts of both higher plants and green algae. The biochemistry of any recombinational mechanism in chloroplasts is completely unknown, however.It is generally accepted that plastids originated from cyanobacterial progenitors, acquired by an ancestral eukaryotic cell through an endosymbiotic event (10,11). Therefore it seemed probable that any chloroplast recombination system should be related to a eubacterial counterpart. In Escherichia coli and many other prokaryotes, the RecA protein is essential for homologous recombination and for a variety of SOS responses to DNA damage (12)(13)(14)(15)(16)(17)(18)(19)(20)

Origins and evolution of the recA / RAD51 gene family: Evidence for ancient gene duplication and endosymbiotic gene transfer

“…4). The N-terminal region of the Arabidopsis RecA1 protein contains a putative chloroplast transit peptide, and the protein was detected in the chloroplast (14). The close relationship of Arabidopsis recA1 and its plants and algae orthologs with cyanobacterial recAs supports the idea that the chloroplast evolved from a cyanobacterion-like endosymbiont in the ancestors of photosynthetic eukaryotes (31).…”

“…Plant RecA proteins also contain a Ϸ70-aa N-terminal region that is different from the RADA͞RAD51 N-terminal regions. At least some plant RecA proteins contain organelle-targeting peptides (14,15). Ancient Duplication Events in the recA͞RAD51 Gene Family.…”

Expression and Complementation Analyses of a Chloroplast-Localized Homolog of Bacterial RecA in the MossPhyscomitrella patens

“…The gene product shares extensive sequence similarity with E. coli RecA protein and chloroplast RecA from A. thaliana 12) and C. reinhardtii 17) except for the amino-terminal region. The PprecA2 transcript possesses two in-frame AUG codons in the 5 0 terminal region.…”

“…19) Moreover, the recA homologs of pea, A. thaliana, and C. reinhardtii chloroplasts perhaps increase after DNA damage. 12,13,17) To examine PprecA2 expression in DNAdamaged cells of P. patens, we analyzed the level of PprecA2 expression in MMS-and bleomycin-treated cells by semi-quantitative RT-PCR and immunoblot analysis using anti-PpRecA2 antiserum. MMS, a DNA methylating agent, perhaps causes double strand breaks (DSBs) by forming methylated bases in DNA, 29) while bleomycin, a radiomimetic DNA-damaging agent, causes DSBs directly.…”

“…9) Homologs of RecA have been identified in plant species, 11) and functions of them in chloroplasts have been suggested. A plant Arabidopsis thaliana cDNA encoding for a bacterial RecA homolog, AtcpRecA (At1g79050), has been isolated, 12) and was found to be targeted to chloroplasts. 13) In pea chloroplasts, strand transfer activity resembling that of bacterial RecA was detected 14) and a protein cross-reacting with the Escherichia coli RecA antibody was identified.…”