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EMBO Plant DNA Repair and Recombination Workshop, Presqu'île de Giens, France 2007
P - 41. Programmed response to IR-induced genomic stress
Kaoru Yoshiyama, Clare Robertson, Kevin Culligan, Anne Britt. Plant Biology, University fo
California, Davis, 95616 Davis, United States
Cellular responses to DNA damage are many and varied. Many of these responses are
programmed, and the complete response requires the presence of multiple signal
transduction pathways. The genetic requirements for these responses can be difficult to
sort out in mammals, as many defects in damage repair or response lead to the induction
of apoptosis. Plants, fortunately, are not as exquisitely sensitive to mismanaged damage,
and so make excellent model systems for the study of the roles of these proteins both in
response to acute damage, and in the general maintenance of unperturbed mitotic and
meiotic cells. Whole-genome analysis indicates that plants, unlike yeasts and mammals,
exhibit a robust transcriptional response to DNA damage that includes many genes
relevant to DNA repair and cell cycle regulation. However, this response is governed, at
least in part, by the same signal transduction components that are required for other
types of damage response in yeasts and mammals. Thus plants may make an excellent
model system for the genetic analysis of DNA damage response. In this presentation we
will focus on our efforts, suing both classical genetic and reverse genetic techniques, to
identify components of the plant DNA damage response pathway.
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P - 42. Identification of genes required for DNA-damage-induced cell cycle arrest
in Arabidopsis
Kaoru Yoshiyama, Anne Britt. Plant Biology, University of California Davis, 95616 Davis,
United States
The genome of a living organism is subjected to a wide variety of genotoxic stresses of
both endogenous and environmental origin. DNA-damage-induced cell cycle checkpoints
are a crucial component of genome maintenance. These checkpoints sense DNA damage,
pause the cell division cycle to provide time for repair, and finally release the cell cycle
from arrest. The mammalian ATM and ATR protein kinases are key proteins involved in
the cell cycle arrest, and Arabidopsis has ATM and ATR homologs. However, in contrast
to yeast or mammalian cells, little is known about DNA damage checkpoint in plants.
AtXPF is a homolog of human repair endonuclease XPF. The xpf mutant of Arabidopsis
can’t form true leaves after irradiation as seeds, showing sensitivity to gamma-radiation.
We screened for suppressor mutants in the xpf background using EMS and isolated sog
(suppressor of gamma radiation) mutants that can form true leaves following radiation,
suggesting that this cell cycle arrest is due to a signaling mechanism rather than to
inhibition of cell cycle by physically blocking the cellular machinery. We have observed
that xpf sog1-1 seeds are hypersensitive to HU (hydroxyurea), an inhibitor of
ribonucleotide reductase. They could germinate on the HU plates, but after that, they
were dead. Surprisingly, when the seeds are grown on “no HU” plates for 5 days, and the
seedlings are transferred to HU plates, the plants can grow as well as wild type. These
results suggest that SOG might be important during or immediately after germination. We
reported that in wild-type Arabidopsis, hundreds of genes are induced in response to
gamma-radiation, and the induction is dependent on ATM. BRCA1, RAD51 and CYCB1;1
transcriptions increased rapidly and strongly. Interestingly, the transcription inductions
of these genes were compromised severely in the xpf sog1-1 mutant, suggesting that the
SOG gene plays an important role in upstream of signal transduction like ATM. (The xpf
mutation does not affect the induction of the genes.) To identify the SOG gene, we’re
currently mapping the mutation, and we know that the SOG gene lies in the vicinity of
CIW12 marker on chromosome I. We are hoping that identifying the function of SOG gene
is a good way to clarify the mechanism of checkpoint mechanism in plants and, perhaps,
in animals.
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