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I am interested in the mechanisms underlying how cells become polar and
how tissue-specific factors and hormones regulate gene expression in
plants. The moss (Physcomitrella patens) is being used
(http://www.biology.wustl.edu/moss) to
study cellular polarity and homologous recombination, while Arabidopsis and
P. patens are the models for analyzing tissue-specific gene expression via the
phytohormone abscisic acid (ABA). Protonemal cells of moss (Physcomitrella
patens) are being used to study cellular polarity, while Arabidopsis is the model for
analyzing tissue-specific gene expression via the phytohormone abscisic
acid (ABA).
When tip growing moss filaments are given an orienting gradient
(e.g. light, gravity), what are the downstream targets for the signaling
path to direct polar growth? Our hypothesis is that since the actin
cytoskeleton has been an essential and central link in our understanding
of polar processes in plants, the protein complexes that regulate the
actin network are the targets for signals that govern polar growth. These
targets can also help to identify interacting proteins that may localize
and stabilize these complexes to the polar site. Hence, our directed
approach is to focus on members of the Arp2/3 and the Wave/SCAR protein
complexes that regulate actin filament formation in other organisms.
Genomic sequences of the several proteins in these complexes are being
used for targeted gene disruption and gene replacement studies (using the
efficient homologous recombination system in moss), in order to assess any
potential role/position in the downstream signaling pathway. We are also
employing a forward genetics approach using insertional mutagenesis and
activation tagging to identify genes that affect polarized growth. These
projects will be greatly aided by the complete sequence of the moss genome
becoming available early in 2007
(http://www.mossgenome.org/).
Projects on gene regulation are focused on the regulatory protein VP1/ABI3
from maize and Arabidopsis and its essential role in
embryo-specific gene expression via the phytohormone abscisic acid (ABA).
Presently we are
identifying the specific domains of VP1/ABI3 that are essential for
nuclear localization and its activity in transcriptional complexes
possessing an ABA-response element in the promoter in responsive genes.
We are interested in the consequences of ectopic expression of ABI3 in
vegetative cells/tissues using chemically-induced promoters. We wish to
determine the spectrum of embryonic genes that can be activated by ABI3 in
non-embryonic cells/tissues as well as any embryo-specific phenotype, i.e.
synthesis of seed storage proteins, desiccation tolerance, etc. A
comparative genomic approach is also underway with homologous genes that
are part of an ABA response pathway that has been conserved between an
early land plant (i.e. moss) and seed plants (~450 million years).
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Twenty-eight-day-old Physcomitrella gametophyte showing the leafy gametophores in the center and the protonemal filaments radiating outward.
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