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Basic research in
plant-microbe interaction.
i. Characterization of Phytophthora spp.
isolated from ornamental crops in central Florida. Various Phytophthora spp are
most frequently isolated from a variety of foliar and woody
ornamental plants in central Florida. Based on
morphological characteristics and previous pathological history of a particular crop, these isolates are tentatively
identified to the species level. However, it is important to
accurately identify these species using molecular analyses.
Many isolates of different Phytophthora
spp that are resistant to Mefenoxam, a commonly used fungicide for
controlling Phytophthora,
have been reported. For managing fungicide-resistance, it is
important to determine prevalence of Mefenoxam
resistant isolates of Phytophthora
strains on ornamental crops. Using molecular phylogenetic
analyses, we are characterizing various Phytophthora isolatesisolated
from 17 genera of ornamental crops. Fungicide sensitivity assays
against several commonly used fungicides will be conducted using standard
procedures.
ii. Calcium and auxin signaling in plant
microbe interaction: Plants use two major
immunity systems to defend themselves against pathogens. In one
system, conserved microbe/pathogen-associated molecular patterns
(MAMP/PAMP) are recognized by plants through “Pattern
Recognition Receptors” (PRRs) leading to the activation of
defense responses (see Fig on right). Pathogens inactivate
PAMP-triggered immunity by delivering virulent disease causing
effectors proteins into cells. Plants counteract by recognizing
these effectors through resistance (R) proteins, which leads to a
more rapid and robust defense system called effector-triggered
immunity. My lab conduct research on certain aspects of both
these pathways. Arabidopsis is a resource-rich model system for
conducting basic plant-microbe interaction studies. Calcium and auxin
are known to play important role in plant defense signaling.
Currently, the molecular mechanisms of how calcium and auxin affect
defense responses are not very well known. Calcium and its
ubiquitous sensor calmodulin (CaM) play
important roles in plant defense. In
order to investigate the role of Ca2+/CaM
in plant defense, we have identified several CaM-binding
proteins that are likely involved in plant-pathogen interaction.
Recently, others and we have shown that CAMTA3 (calmodulin-binding
transcription activator 3 ; also called
AtSR1 for Arabidopsis thaliana Signal
Response 1 ) and its rice homolog (OsCBT)
negatively regulate plant immunity. Loss-of-function camta3 mutants display
constitutively elevated SA, PR
genes and resistance to bacteria. Our group is currently
investigating several important questions related to calcium and
auxin signaling using molecular, cell biological, genetic and
physiological approaches. Understanding the calcium and
auxin-signaling pathway components can lead to engineering crops for
enhanced resistance against plant pathogens.
iii. Y2H hybrid screen for identifying
proteins that interact with Phytophthora effector proteins.Bioinformatics analyses of genome sequences of
several Phytophthora
species have revealed an extraordinarily large number of secreted
disease effector proteins. Some of these effectors function in
the plant extracellular spaces (apoplasts),
whereas others are injected inside plant cells and are suggested to
attenuate plant defense responses for promoting pathogen
colonization. To understand the molecular basis of how the Phytophthora effectors
alter plant physiology, it is important to identify their targets in
host plants, and to understand their role in pathogenesis. Using
several molecular and cell biological approaches, we are
investigating several questions about how Phytophthora cause disease in host plants.
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