The key discovery by the Timmermans team, which appears online today in the journal Genes & Development, is the identification of the mechanism that brings PRC2 to specific sites along the genome precisely in those cells committed to become a leaf.
Timmermans' team showed that PRC2 physically interacts with DNA binding proteins that attach to plant DNA in specific genome regions just ahead of where the homeobox genes are situated. In the plant they studied, Arabidopsis, those DNA binding proteins are ASYMMETRIC LEAVES1 (AS1) and AS2. When a stem cell commits to becoming a leaf cell, AS1 and AS2 become active, attach at the DNA sites near BP and KNAT2, and recruit PRC2 to repress these homeobox genes. The epigenetic mark made by PRC2, which acts like a cellular memory, is heritable, and is essential in order for leaves and other plant organs to develop.
In other locations along the genome, other analogous mechanisms are surely at work, says Timmermans, whose broad interest in this research concerns its implications for patterning in development.
Timmermans is intrigued to learn the effects of tweaking with the timing of regulatory gene expression and repression. She suspects small adjustments to expression of master regulators during development are one of the means by which evolution proceeds over vast stretches of time.
She also notes that by tweaking these developmental regulatory systems, it might be possible to beneficially affect plant regeneration the process in which a new plant is generated from the leaf of an existing one. This process involves de-differentiating a mature cell and returning it to a primitive developmental state before once again allowing it to proceed down a developmental path a process akin to that employed in the making of human IPS (induced pluripotent stem) cells.
|Contact: Peter Tarr|
Cold Spring Harbor Laboratory