Fellow 1992-93

Thomas W Jacobs

Plant Biology

A Higher Plant Cell Division Induction Pathway

All life forms are composed of cells, each of which is the product of the division of a parent cell into two progeny cells. This process of cellular reproduction, also known as mitosis, must be very stringently regulated in all plants and animals; otherwise, life-threatening conditions such as cancer can ensue. We have recently isolated an alfalfa plant gene which encodes an enzyme, MsERK1, homologues of which in animal systems are involved in transducing the chemical messages of soluble cell division inducers (mitogens) into cellular division responses. This enzyme is a protein kinase; that is, it adds phosphate groups to, and thereby activates, other cellular proteins, as part of a cascade of mitogenic signal transduction. This is the first signal transduction protein kinase of known function to be identified in the plant kingdom, and constitutes the first evidence that a system analoguous to a well-characterized animal cell mitogenic induction pathway is operative in plants. Elucidating the biochemical steps upstream of MsERK1 activation will provide valuable insights into plant cell signal transduction, cell division control, and morphogenesis. 

Professor Jacobs and his team have found that MsERK1 autophosphorylates when expressed in bacteria. The first experiments to be performed under the auspices of this fellowship will constitute a detailed characterization of this autophosphorylation phenomenon in order to assess its relation to the signaling pathway in the plant. Data thus obtained will be used to design experiments aimed at identifying the MsERK1 activator, the previous step in the signal transduction cascade. Alfalfa protein extracts will be prepared, fractionated, and assayed for activity as MsERK1 activators. Such a strategy will provide the first glimpse of elements of this essential response pathway in a higher plant and will pave the way for subsequent progress in an important and uncharted domain of plant cell biology.