Professor
Ph.D., Rutgers University, 1996

small RNA regulation, pattern formation, stem cell function, plant development

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Plants grow and develop organs, such as leaves, throughout their lifetime. The growing tips of plants contain a population of indeterminate stem cells that serve as a persistent source of daughter cells from which new organs arise. We are studying the epigenetic mechanisms that distinguish indeterminate stem cells from differentiating cells in plants. One pathway involves the highly conserved Polycomb Repressive Complex2 that establishes a repressive chromatin mark at stem cell promoting genes during organogenesis. We are taking a genomics approach to identify novel PRC2 targets and are investigating the mechanism that recruits the PRC2 complex to these genes, a key question also in the mammalian stem cell field.

A second objective of our research is to elucidate the mechanisms via which small regulatory RNAs create developmental patterns. Dorsoventral polarity in leaves is specified through a cascade of small RNAs. Importantly, we have shown that these small RNAs are mobile and move from their source of biogenesis to create accumulation gradients across the leaf. The opposing mobile small RNA gradients form a stable and precisely defined boundary between the upper and lower sides of the leaf that drives its outgrowth and differentiation. Our current research efforts are aimed at characterizing genes involved in the regulation of this small RNA network, and at understanding the mechanisms via which small RNAs are able to move from cell to cell and function as morphogen-like instructive signals to create developmental patterns.

 

Selected Publications

Chitwood, D.H., and Timmermans, M.C.P. 2010. Small RNAs are on the move. Nature 467: 415–419.

Chitwood, D.H., Nogueira, F.T.S., Howell, M., Montgomery, T.A., Carrington, J.C., and Timmermans, M.C.P. 2009. Pattern formation via small RNA mobility. Genes Dev. 23: 549–554.

Nogueira, F.T.S., Madi, S., Chitwood, D.H., Juarez, M.T., and Timmermans, M.C.P. 2007. Two small regulatory RNAs establish opposing fates of a developmental axis. Genes Dev. 21: 750–755.

Guo, M., Thomas, J., Collins, G., and Timmermans, M.C.P. 2008. Direct repression of KNOX loci by the ASYMMETRIC LEAVES1 complex of Arabidopsis. Plant Cell 20: 48–58.

Juarez, M.T., Kui, J.S., Thomas, J. Heller, B.A., and Timmermans, M.C.P. 2004. microRNA mediated repression of rolled leaf1 specifies maize leaf polarity. Nature 428: 84–88.