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Purdue Motility Group
Biological Sciences
Pollen Projects
Profilin and Corn POPs
Supported by the USDA-NRICGP (94-37304-1179, 97-35304-4876 & 99-35304-8640)
Staff: Faisal Chaudhry & Dr. Tracie Matsumoto
Summary:
A remarkable example of cellular morphogenesis, pollen germination and tube growth,
is essential for plant reproduction. In order to deliver non-motile sperm to
the embryo sac, the vegetative cell of the pollen grain forms a tip-growing protuberance
that extends at rates up to 1 cm/h. A dynamic network of filaments and associated
proteins, the actin cytoskeleton, organizes the pollen cytoplasm, provides the
molecular railroad tracks for cytoplasmic streaming, and orchestrates the delivery
of secretory vesicles to the growing apex. To understand the molecular mechanism
of tip growth, we have focussed attention on a gene family for the actin monomer-binding
protein, profilin, from the crop plant Zea mays. Our central
hypothesis is that profilin is a fundamental regulator of actin polymerization
and its cellular function is mediated through interactions with a diverse set
of binding partners. We have already characterized the interaction of recombinant and native maize
profilins with three major ligands (G-actin, PtdIns(4,5)P2 and polyproline) and
discovered several important differences between plant and non-plant profilins
and among plant profilin isoforms. Live cell and in vitro mutagenesis studies
demonstrate that profilin binding to both actin and proline-rich sequences is
important for cellular function. In this proposal we will test two
working hypotheses.
First, we propose that the major function of pollen profilin is to bind actin
monomers and prevent actin polymerization, i.e. profilin is a simple sequestering
protein. The second hypothesis is that pollen contains novel and previously identified
interacting proteins, or partners of profilin (POPs), which regulate profilin
function. Biochemical, cytological and genetic experiments are designed to test
these hypotheses. This research is significant because it will provide detailed
understanding of the strategies used by plant cells to regulate actin organization
and function. Furthermore, it provides the potential to uncover plant-specific
mechanisms that underpin cytoplasmic organization, cell polarity, and vesicle
trafficking. Our findings will dramatically improve knowledge of pollen biology
and provide tools and approaches for manipulation of plant sexual reproduction.