Why It Is Important

Plant innate defense against fungal, bacterial, and viral pathogens is a topic of central agricultural importance because, after the physical barriers, innate defense provides the first line of protection and is responsible for activating other defense mechanisms. Additionally, reaction of the host to an invading pathogen is itself an important aspect of disease development separate from direct pathogen effects. Effector interaction with its cognate immune receptors is the first critical step in activating plant defense responses against the invading pathogen, but very little is known about the molecular details of this interaction.

Our understanding of pathogen-plant interactions has advanced significantly in recent years. Many pathogen molecules have been identified, mostly protein effectors, that facilitate success of the pathogen against the plant. Similarly, plant molecules, most termed immune receptor proteins, recognize various pathogen molecules and signal the plant’s defense system to take protective action. Researchers now have an outline of how the recognition and reaction events occur. Understanding such events on the atomic level is needed in order to create entirely new approaches to improving plant protection. To date, few molecular structures of pathogen effectors, and none of a complete immune receptor, have been obtained. This project aims to remedy this situation.

Our Approach

Our theme faculty of plant molecular biologists and protein-structure researchers is advancing the molecular biology and biochemistry of effectors and immune receptors by several parallel approaches, most importantly by obtaining 3-dimensional structures of these molecules and their complexes. There is only very limited ability to predict which specific protein will be amenable to structural analysis, and only at the end of a long series of steps does the investigator discover which protein yields a structure. These steps include molecular cloning, protein modification and production to obtain suitable amounts in solution, and function testing to determine whether the protein structure, if obtained, will have biological relevance. Protein solutions then are subjected to hundreds of trial conditions to produce protein crystals. Only some crystals are suited to structure determination by x-ray crystallography.

Impacts & Highlights

• Determined the structure for a new fungal elicitor; binding properties of three fungal elicitors were compared by numerous biological and chemical tests
• Demonstrated that fungal core effector proteins may have functions beyond suppression of host immunity and can act to adapt the fungus to varied environments
• Exploited a small lectin protein of animal origin to identify structural features; identified a subcellular binding site for which no function had been known of fungal elicitors
• Purified a few immune receptor proteins by newly developed methods that yielded highly active proteins showing extensive self-phosphorylation and trans-phosphorylation
• Applied an insect cell protein expression system to obtain large amounts of soluble immune receptor protein for crystallization; numerous attempts to produce these proteins in Escherichia coli (E. coli) or yeast were not successful

Team

George Bruening	Professor Emeritus of Plant Pathology
Gitta L. Coaker	Associate Professor of Plant Pathology
S.P. Dinesh-Kumar	Professor of Plant Biology
Andrew J. Fisher	Professor of Molecular & Cellular Biology and Chemistry
Ioannis Stergiopoulos	Associate Professor of Plant Pathology
David Wilson	Professor of Molecular & Cellular Biology
Yi-Hsuan Chiang	Postdoc of Plant Pathology
Amanda Kohler	Postdoc of Plant Pathology
Burinrutt Thanasuwat	Junior Specialist of Plant Biology
Afsoon Bediei	Junior Specialist of Plant Biology
Anthony Salvucci	Staff Research Associate of Plant Sciences
George Kamita	Staff Research Associate of Entomology and Nematology
Nicholas Hurlburt	Graduate Student of Chemistry
Neeraj K. Lal	Graduate Student of Molecular & Cellular Biology
Donghyuk Lee	Graduate Student of Plant Pathology
Melissa Matthews	Graduate Student of Chemistry
Anna Nowak	Graduate Student of Molecular & Cellular Biology
Crystal Liu	Undergraduate Student of Biochemistry & Molecular Biology
Chie A. Ueda	Undergraduate Student of Molecular & Cellular Biology
Janet Tan	Undergraduate Student of Biochemistry & Molecular Biology
Jonghoon Chan	Undergraduate Student of Biochemistry & Molecular Biology
Christine Do	Undergraduate Student of Biochemistry & Molecular Biology
Gloria Pai	Undergraduate Student of Chemistry
Rosalva Flores	Undergraduate Student of Biochemistry and Molecular Biology
Alexander Nagourney	Undergraduate Student of Biochemistry and Molecular Biology
Yongam Lee	Undergraduate Student of Biochemistry and Molecular Biology
Gita Mallya	Undergraduate Student
Jesus Banderas	Undergraduate Student of Plant Pathology
Nicholas Fung	Undergraduate Student of Plant Pathology
Dean Poz	Undergraduate Student of Cell Biology

For more information on this program, please contact Christine Parks ceparks@ucdavis.edu.