UC DavisのDr. Kentaro Inoue&s_comma; Dr. Anne Brittのセミナーを下記のように開催いた
１．3/17（火）14:00-15:00 東京理科大学野田キャンパス 計算科学研究センター4
講演者: Dr. Kentaro Inoue
Associate professor&s_comma; Department of Plant Sciences&s_comma; UC Davis
"Protein conducting channel in the outer membrane of the chloroplast
envelope - a model to study organelle biogenesis"
Chloroplasts have evolved through endosymbiosis from an ancestral
cyanobacterium&s_comma; and now support viability of almost all organisms on earth
via their various metabolic functions including photosynthesis. During
evolution&s_comma; the endosymbiotic organelle generated systems to import proteins
from the cytoplasm&s_comma; and eventually transferred most of its genes to the host
nucleus. Thus&s_comma; establishment of protein import apparatus is a prerequisite
for the biogenesis of chloroplasts in both evolutionary and developmental
contexts. The β-barrel-forming membrane protein Toc75 is essential for
viability of plants by serving as a protein import channel at the
chloroplast outer envelope. It is nuclear-encoded and synthesized in the
cytoplasm with a cleavable targeting sequence. Despite its importance&s_comma;
however&s_comma; the mechanism by which Toc75 is sorted to and assembled in the
membrane remained largely elusive. Furthermore&s_comma; although the prokaryotic
origin of Toc75 has been indicated&s_comma; the process by which it was converted to
the protein import channel is unknown. Our research program has been
evolving from the following three questions about Toc75.
1. How is it sorted to the chloroplast outer envelope?
2. How is its targeting sequence removed?
3. How was a bacterial protein converted to the organelle protein import
Addressing the first question has led us to identify a novel mechanism of
protein targeting to the chloroplast envelope&s_comma; which is shared by multiple
proteins and also should be useful for future chloroplast engineering.
Answering the second question has provided us with a new tool that allows us
to elucidate a long-standing problem&s_comma; "how are the photosynthetic membrane
systems developed?" Our recent findings about a paralog to Toc75 in the
chloroplast outer envelope have helped us develop testable hypotheses to
solve this evolutionary problem.
２．3/18（水）13:30-15:00 東京理科大学野田キャンパス 計算科学研究センター4
講演者: Dr. Anne Britt
Professor&s_comma; Department of Plant Sciences&s_comma; UC Davis
"The NAC domain transcription factor Suppressor of Gamma Response 1 (Sog1)
governs programmed response to DNA damage"
All living things possess mechanisms to detect the presence of DNA damage
and transduce that signal to induce a variety of responses. These responses
include the activation of repair&s_comma; the arrest of the cell cycle&s_comma; and the
induction of programmed cell death. In Arabidopsis the response to
chromosome-breaking agents includes the robust upregulation of hundreds of
genes&s_comma; including many genes that are clearly involved in DNA repair. This is
a specific response to double strand breaks: the spectrum of genes induced
by gamma radiation does not include the genes known to be induced by a
variety of other abiotic stressors&s_comma; and the transcriptional response is
entirely dependent on the PI3K-like protein kinase ATM&s_comma; a protein known to
be activated by double strand breaks. Such a response is unprecedented-
mammals and yeast do not exhibit this robust and specific induction of
repair-related genes in response to double strand breaks.
As a result of a search for mutants defective in gamma-induced cell cycle
arrest&s_comma; a line carrying a "gamma resistant" mutation&s_comma; termed sog1&s_comma; was
identified. This mutation was mapped and cloned&s_comma; and SOG1 was revealed to
be a member of the large family of NAC domain transcription factors.
Further analysis of sog1 revealed that this gene&s_comma; like ATM&s_comma; is required for
the transcriptional response to gamma radiation. Here we will present
evidence that SOG1 is also required for the programmed&s_comma; tissue-specific cell
death response to DNA damage observed in Arabidopsis. Thus SOG1&s_comma; although
unrelated to the mammalian transcription factor and tumor suppressor TP53&s_comma;
evolved independently in multicellular plants to play the same essential
role in governing DNA damage response.
なお、Dr. Inoue&s_comma; Dr. Brittの講演は、3/16(月)にホテルメトロポリタンエドモント