Professor, & Cy Mouradick Endowed Chair
Director of Genetics,Genomics and Bioinformatics Graduate Program
Department of Plant Pathology and Microbiology
Center for Plant Cell Biology
Institute for Integrative Genome Biology, University of California, Riverside
Biography & Research Interests
My lab studies the molecular mechanisms of plant immunity and pathogen virulence, with an overall goal to develop effective and environmentally friendly strategies to control plant diseases and to ensure sufficient food production.
Our research projects include:
Small RNAs, including microRNAs (miRNAs) and small interfering RNAs (siRNAs), are important regulators of eukaryotic gene expression by guiding mRNA cleavage, translational inhibition or chromatin modification. We utilize genomics, genetics, molecular and biochemical approaches to identify and functionally characterize infection-regulated small RNAs, including those from plant hosts and from eukaryotic pathogens. My lab provided the first example of a plant endogenous siRNA that regulates plant immune responses. We further discovered that some small RNAs from aggressive fungal pathogens are delivered into host cells to hijack host RNAi machinery to suppress host immunity genes. These studies have added small RNAs to the list of pathogen effectors, which unveiled a novel virulence mechanism in aggressive eukaryotic pathogens. The transport of small RNAs from fungal pathogens to plant hosts also represents a naturally occurring cross-kingdom RNAi event. We recently show that such cross-kingdom RNAi is bi-directional, plants are also capable of delivery small RNAs into fungal pathogens to attenuate their virulence.
My lab also studies the function and regulation of RNAi pathway components, mostly Argonaute (AGO) proteins in plant immunity. AGO proteins are the core components of RNAi complexes, which selectively bind with small RNAs and silence target genes with complementary sequences. We discovered that Arabidopsis AGO2 positively regulates antibacterial immunity by associating with miR393*, which targets a Golgi-localized SNARE gene MEMB12 and leads to increased secretion of antimicrobial peptide and confers resistance. Since miR393 also contributes to antibacterial immunity by suppressing auxin receptors, miR393*/miR393 represent a novel example of a miRNA*/miRNA pair that functions in the same cellular pathway (host immunity) through two distinct AGOs. We further demonstrated that small RNA duplex structures and AGO PIWI domain contribute to the selective loading of small RNAs in different AGO proteins, AGO1 and AGO2. We currently focus on the regulation and modification of AGO proteins in responses to pathogen attacks.
Surveillance of pathogen infection is mediated by intracellular NOD-like nucleotide-binding/leucine-rich-repeat receptors (NLRs) in both plants and animals. We recently discovered that some NBS-LRR genes, are under the control of specific plant chromatin remodeling proteins, as well as RNA-directed DNA methylation (RdDM) pathway. Such epigenetic regulation ensures precise expression of these resistance genes to avoid autoimmune responses or disease.
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