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The little mustard Arabidopsis and the tobacco plant are both dicots, but
the latter?s genome is over twenty times larger, even as Arabidopsis? is
more complex. What, then, spells the difference and complexity? Holger
Puchta of the University of Karlsruhe, Germany attempts to answer the
question in the latest issue of The Journal of Experimental Botany, December
2004.

In ?The repair of double-strand breaks in plants: mechanisms and
consequences for genome evolution,? Puchta looks at various proposed
techniques for DNA repair in plants, especially for damage caused by
double-strand breaks (DSBs). DSB repair is important for the survival of all
organisms, as it has to be performed before genomes can be replicated; and,
considering that it entails removing or replacing entire stretches of DNA,
it may be the key to understanding why some plants have more DNA than
others, or why some genes are missing or duplicated.

Generally, DSB?s can be repaired by either homologous recombination (HR),
where sequences are linked in regions that are nearly identical in sequence
to each other; or non-homologous end joining (NHEJ); also known as
illegitimate recombination, where DNA sequence information does not play a
major role in the rejoining of the two double strands.

Since sequence substitution or removal are involved, induced DSB?s and DSB
repair may also one day be used in the controlled induction of genomic
changes in plants, Puchta says.

For a more detailed discussion of DSB repair, download the review at
[jxb.oupjournals.org]

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