Root assays to study pattern-triggered immunity in plant-nematode interactions

Authors: TRAN, TIEN - Cornell University; CHEN, SHIYAN - Cornell University; Wang, Xiaohong

Submitted to: European Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/14/2016
Publication Date: 9/23/2016
Citation: Tran, T., Chen, S., Wang, X. 2016. Root assays to study pattern-triggered immunity in plant-nematode interactions. European Journal of Plant Pathology. 147:955-961.

Interpretive Summary: Plants are equipped with a robust immune system to defeat pathogen attack. The first level of immunity involves the recognition of conserved features of pathogens, leading to pattern-triggered immunity (PTI) which protects plants against most pathogen invasions. However, adapted plant pathogens have evolved effectors to suppress PTI, thus enabling successful infection. Plant-parasitic nematodes are among the most devastating plant pathogens causing significant crop losses worldwide. Accumulative evidence has indicated that plant-parasitic nematodes use secreted effector proteins to suppress PTI to promote infection. Understanding how nematodes use their effectors to manipulate plant immunity is necessary for developing novel nematode control strategies. PTI assays used in the study of nematode effectors are often conducted in plant leaves, which are a non-host tissue for most nematode species. Therefore, there is a need for robust PTI assays in roots of host plants. In this study, we tested four candidate elicitors for their effectiveness in activating PTI responses in roots of two economically-important crops of tomato and potato and found that three of the tested elicitors are potent in inducing PTI responses in tested roots, demonstrating for the first time of PTI in roots of crop species. We further used the developed PTI assays to confirm a role of two nematode effectors in PTI suppression. In summary, this study has successfully established PTI assays in plant roots, which provides a valuable tool that will facilitate the study of nematode pathogens as well as other root pathogens in their manipulation of plant immunity.

Technical Abstract: Plants employ extracellular immune receptors to perceive conserved pathogen-associated molecular patterns (PAMPs), triggering the first layer of defense known as pattern-triggered immunity (PTI). The understanding of PTI is mainly based on the studies focusing on leaves. Plants are vulnerable to attack by various root pathogens including plant-parasitic nematodes. Evidence is accumulating that phytonematodes utilize their secreted effectors to suppress PTI to enable successful infection. PTI assays used for characterizing nematode effectors are often conducted in the non-host plant or tissue, such as leaves. Thus, there is a need for PTI assays in roots of host plants. Here, we tested four candidate elicitors flagellin 22 (flg22), flgII-28, and two nonpathogenic bacteria Pseudomonas fluorescens and P. syringae strain DC3000'hrcU for their effectiveness in activating PTI responses including the induction of defense gene expression and callose deposition in roots of two economically-important Solanaceae crops of tomato and potato. We found that flg22 and the two bacteria are potent in inducing defense gene expression and callose deposition in tested roots, revealing for the first time of PTI in roots of Solanaceous plants. Effectors of GrCEP12 and Hs10A06 are previously indicated to involve in PTI suppression. Consistently, upon treatment with the elicitor, roots of transgenic plants expressing GrCEP12 or Hs10A06 showed a reduced level of defense gene expression and callose deposition compared to those of control plants. Taken together, our established root PTI assays represent a valuable tool that will facilitate the study of nematode pathogens and other root pathogens in their manipulation of plant immunity.