How do bacteria infect plants and how do plants defend themselves from such attacks?
The Martin laboratory studies the molecular basis of bacterial infection processes and the plant immune system. The research focuses on speck disease which is caused by the infection of tomato leaves with the bacterial pathogen Pseudomonas syringae pv. tomato. This is an economically important disease that can decrease both the yield and quality of tomato fruits. It also serves as an excellent system for studying the mechanisms that underlie plant-pathogen interactions and how they have evolved. Many experimental resources including an increasing number of genome sequences are available for both tomato and P. s. pv.tomato. Current work relies on diverse experimental approaches involving methods derived from the fields of biochemistry, bioinformatics, cell biology, forward and reverse genetics, genomics, molecular biology, plant breeding, plant pathology and structural biology.
In the tomato-Pseudomonas interaction, the plant responds rapidly to a potential infection by detecting certain conserved molecules expressed by the pathogen. At this stage the pathogen uses a specialized secretion system to deliver virulence proteins, such as AvrPto and AvrPtoB, into the plant cell. These proteins suppress early host defenses and thereby promote disease susceptibility. Some tomato varieties express a resistance gene, Pto, which encodes a protein that detects the presence of AvrPto or AvrPtoB and activates a second strong immune system that halts the progression of bacterial speck disease.
The Martin lab is currently studying many aspects of the molecular mechanisms that underlie the bacterial infection process and the plant response to infection. One project takes advantage of the genetic natural variation present in wild relatives of tomato to identify new genes that contribute to plant immunity. These genes provide insights into the plant immune system and also can be bred into new tomato varieties to enhance disease resistance. A second project relies on next-generation sequencing methods to identify tomato genes whose expression increases during the interaction with P. s. pv. tomato. The expression of these genes is then reduced by using virus-induced gene silencing or they are mutated using CRISPR/Cas9 to test whether they make a demonstrable contribution to immunity. A third project uses photo-crosslinking and other biochemical methods to characterize plant proteins that play a direct role in recognizing the conserved bacterial molecules that activate the early plant immune system.
The long-term goal in this research is to use the knowledge gained about the molecular basis of plant-pathogen interactions to develop plants with increased natural resistance to diseases. Such plants would require fewer applications of pesticides producing economic and environmental benefits while providing food for consumers with less pesticide residue.
The Martin laboratory studies the molecular basis of plant immunity and bacterial pathogenesis. Our focus is on the infection of tomato by Pseudomonas syringae pv. tomato as this interaction results in bacterial speck, an economically important disease, and also serves as a powerful model system for understanding fundamental mechanisms involved in plant-pathogen biology. On the bacterial side, we study virulence proteins and associated mechanisms that the pathogen uses to interfere with the plant immune response. On the plant side, we identify and characterize genes, proteins and molecular mechanisms that play a role in host immunity and susceptibility. Our work relies on natural variation for these traits that is present in cultivated tomato and in the 12 wild relatives of tomato that originated in South America. For the characterization of both plant and bacterial genes and proteins, we use a variety of experimental approaches including biochemistry, bioinformatics, genetics, genomics, molecular biology, and structural biology.
Examples of research projects in my laboratory include: 1) Using tomato varieties that have natural variation in their immune system to clone and characterize the genes responsible; 2) Using CRISPR/Cas9 genome-editing methods to mutate immunity-associated genes and investigate alterations in the plant defense system; and 3) Investigating bacterial proteins that play a key role in promoting pathogenesis and virulence.
Representative publication: https://nph.onlinelibrary.wiley.com/doi/abs/10.1111/nph.15788
Interns in the Martin Lab are funded by NSF IOS-1451754 and REU-1358843.
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