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EMBO Plant DNA Repair and Recombination Workshop, Presqu'île de Giens, France 2007
P - 17. Functional analysis of the OsEZ polycomb group gene in rice
Doolyi Kim, Myungsuk Jung, Insun Yoon, Yeonhee Lee, Seokcheol Suh. Cell and Genetics,
National Institute of Agricultural Biotechnology, 441-707 Suwaon, South Korea
The epigenetic control of gene expression is equally important in plants. Genetic and
molecular analyses in recent years have started to illuminate how products of these
multiple genes interact to initiate seed development. PcG proteins are known to form
multimeric complexes that modulate gene expression by changing higher order
chromatin structure. In this study, EZ gene was isolated and characterized from rice. A
full-length EZ cDNA was obtained by reverse transcriptase (RT)-PCR. EZ gene is producted
to encode a protein of 895 amino acid with an estimated molecular 99.8 kDa. The EZ
protein contains a characteristic SET domain. To identified interaction of EZ gene with
polycomb group protein, we also present evidence, from yeast two-hybrid experiment, of
physical interaction of EZ and FIE proteins, as would be expected in a polycomb type
system. Also, the EZ cDNA was inserted into binary vector pMJ-Cytc. The vectors
described above were introduced into Agrobacterium tumefaciens strain LBA4404 to
obtain a transgenic plants. We have obtained transgenic lines from rice. The phenotype of
transgenic plants were investigated for functional characterization of EZ gene.
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P - 18. A Novel Model for Chloroplast Replication Mechanism in Green Plants
Neeraja Krishnan, Basuthkar Rao. Department of Biological Sciences, Tata Institute of
Fundamental Research, 400005 Mumbai, India
A Novel Model for Chloroplast Replication Mechanism in Green Plants Neeraja M.
Krishnan*, Basuthkar J. Rao Correspondence Address: B-202, Department of iological
Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai –
400 005 INDIA Email Address: neeraja@tifr.res.in, bjrao@tifr.res.in Abstract Chloroplast
replication mechanism, despite 30 years of work, is still sketchy and not well understood.
The initial proposition of rolling circle, bi-directional replication mechanism in tobacco
and pea chloroplast genomes is now being questioned by the new hypothesis of
homologous recombination-mediated replication based on complex, branched multimeric
forms of these molecules. We address this issue of uni- vs. bi-directional replication by
analyzing nucleotide composition in the regions between known replication origins, with
an aim of revealing any cytosine to thymine deamination gradients. These gradients
typically result from accumulation of deaminations over the extent of singlestrandedness
experienced by the genome and can, therefore, be used as a strong
signature of single-strandedness. Such analyses can thus, throw more light on the singlestrandedness
levels experienced by these regions during replication. Fine-mapping of
replication origins on tobacco chloroplast genome revealed two pairs of replication
origins (A which folds into a simple linear hair-pin form, and B with a complex D-Loop
like form), one pair on each inverted repeat. We found homologues of these replication
origins on other Viridiplantae chloroplast genomes, using NCBI pair-wise BLAST tool. Our
linear regression analyses on the nucleotide compositions of the non-coding regions and
the synonymous third codon position of the coding regions, between any two replication
origins, reveal existence of C to T deamination-type mutation gradients. We find
increasing gradients for C to T deaminations in the regions interspersed between the
complex origins B on either inverted repeat, only on one strand, suggesting unidirectional
replication. These C to T gradients were however, found for both the strands
in the region between origins A and B, on each inverted repeat. This indicates singlestrandedness
on both strands, suggesting bi-directional replication. The larger region
between the pair of origins, A on each inverted repeat again reveals increasing C to T
deaminations only on one strand, suggesting uni-directional replication. We summarize
and present these results in the form of a model for replication mechanism in chloroplast
genomes.
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