Plant Pathology Graduate Program

Wenbo Ma

Wenbo Ma
Office: 951-827-4349
Fax: 951-827-4294
1234C Genomics Building
Office Hours: , not specified - not specified
Email: wenboma@ucr.edu

Wenbo Ma


Molecular Plant-Pathogen Interactions

Ph.D. (2003) in Biology, University of Waterloo, Canada


LAB WEBPAGE: www.wenboma.ucr.edu

Biography & Research Interests

My laboratory studies the molecular mechanisms underlying microbial pathogenesis. In particular, we are interested in elucidating the strategies employed by bacteria and oomycete pathogens to facilitate the establishment and maintenance of symbiotic relationship with plant hosts. A combination of molecular biology, comparative genomics, functional genomics, genetics, biochemistry, bioengineering and bioinformatics approaches is utilized to accomplish these goals. Novel knowledge obtained from our research will contribute to the development of sustainable control strategies against these destructive plant diseases.

The main focus of our research is a group of specialized virulence proteins, called effectors, which are secreted from the pathogens and directly manipulate specific physiological processes or signaling pathways in host cells for the benefit of infection. A broad range of parasites, including viruses, bacteria, fungi, oomycetes, protozoa, insects and nematodes, subvert host immunity through the functions of effectors. The main questions that we are trying to answer include: 1) how do effectors promote pathogen infection; and 2) how do they evolve during the arms race with their hosts.

Type III effectors of bacterial pathogens

Gram-negative bacteria rely on a specialized, needle-like protein secretion system, the type III secretion system, to inject effectors directly into the host cytoplasm. Type III secretion system is a key pathogenicity determinant of pathogens that are responsible for some of the most devastating diseases on animals and plants. Type III effectors (T3Es) directly target with their host substrates and contribute to disease development. As a counter-attack strategy, plants evolved resistance (R) genes that recognize specific T3Es and trigger defense responses. However, this effector-triggered immunity (ETI) could be effectively evaded by the pathogens, which would then regain the ability to cause diseases. To date, the molecular basis of effector evolution remains poorly understood.

We use the model plant bacterial pathogen Pseudomonas syringae and its natural host soybean to investigate the evolution of type III effectors. In particular, our work has focused on the HopZ1 effectors, which belongs to the widely distributed YopJ effector family that possesses a novel Ser/Thr/Lys acetyltransferase activity. We are interested in understand the virulence function and the enzymatic activity of the HopZ1 effectors. Some of our recent findings are published in Ma et al. (2015), New Phytologist; Zhang et al. (2016), Nature Structure and Molecular Biology; Ma and Ma (2016) Microbiology and Molecular Biology Review; Zhang et al., (2017), Nature Plants.

RxLR effectors of Phytophthora pathogens

Phytophthora are responsible for many devastating diseases on important crops including potato, tomato, melon, and soybean. The potato pathogen Phytophthora infestans triggered the Irish Famine in the 19th century and remains a major threat of solanaceous crops worldwide. Other important pathogens include Phytophthora sojae, the second most destructive pathogen of soybean, and Phytophthora ramorum, the culprit of the suddent oak death. Genome sequence analysis revealed hundreds to over one thousand effector proteins from each Phytophthora species. Many effectors contain a conserved N-terminal RxLR motif, which mediates their intake into host cells. The functions of the vast majority of Phytophthora effectors remain unknown.

We identified two Phytophthora effectors that suppress RNA silencing in plant hosts (Qiao et al., Nature Genetics, 2013; Qiao et al., PNAS, 2015). RNA silencing is a universal gene regulation mechanism in eukaryotes dependent on 20-30 nucleotide (nt) small RNAs. Accumulating evidence suggest that small RNAs are integral regulators of plant immunity. We investigate the molecular mechanisms underlying the RNA silencing suppression activity and the virulence function of these Phytophthora Suppressors of RNA silencing (PSRs), which will reveal a new paradigms in plant-pathogen arms race. 

Effectoromics of the destructive citrus Huanglongbing (HLB)

Global citrus production is facing an unprecedented threat from Huanglongbing (HLB, aka citrus greening disease). HLB is associated with the bacterial pathogen Candidatus Liberibacter asiaticus (CLas) in the US. Transmitted by the insect vector called psyllids, CLas colonizes the phloem tissue (the vascular system of plants) in citrus trees and eventually causes tree death. So far, there is no cure once the trees are infected by CLas. 

My group pursues to develop diagnosis tools and resistance varieties to HLB. For these purposes, we study the effectors produced by CLas and dispersed in the phloem of infected trees. We have successfully developed an ELISA-based diagnosis method using an effector as biomarker (Pagliaccia et al., 2017, Front Microbiol). A major research focus in the lab is to identify host target(s) of these CLas effectors and understand how they contribute to HLB pathogenesis. This knowledge is foundamental for HLB biology and essential to generate HLB-resistant citrus. 


Schroth Faces of the Future Award, American Phytopathological Society, 2012

Regent's faculty fellowship, 2008-2009

Natural Sciences and Engineering Research Council of Canada Postdoctoral Fellowship, 2003-2005

W.B. Pearson Medal, University of Waterloo, 2003

E.B. Dumbroff Award, University of Waterloo, 2003


  1. Pagliaccia, D., Shi, J., Pang, Z., Hawara, E., Clark, K., Thapa, S., Francesco, A., Liu, J., Tran, T., Bodaghi, S., Folimonova, S., Ancona, V., Mulchandani, A., Coaker, G., Wang, N., Vidalakis, G., Ma, W.* (2017) A pathogen secreted protein as a detection marker for citrus Huanglongbing. Frontier in Microbiology. 8: 2041.
  2. Bailey-Serres, J., Ma, W. (2017) An immunity boost combats crop disease. Nature. 545: 420-421. doi: 10.1038/nature22497.
  3. Zhang Z. #, Ma K-W. #, Gao L. #., Hu Z., Schwizer S., Ma W.*, Song J*. (2017) Mechanism of host substrate acetylation by a YopJ family effector. Nature Plants. 3: 17115. (# co-first authors)
  4. Kong L., Ye W., Dong S., Ma W., Wang Y*. (2017) A Phytophthora effector regulates host histone acetylation and reprograms defense gene expression to promote infection. Current Biology. 27: 981-991.
  5. Ma K-W.*, Ma W.* (2016) YopJ family effectors promote bacterial infection through a unique Ser/Thr/Lys acetyltransferase activity. Microbiology and Molecular Biology Reviews. 80: 1011-1027.
  6. Zhang Z. #, Ma K-W. #, Yuan S., Luo Y., Jiang S., Pang S., Ma W.*, Song J*. (2016) Structure of a pathogen effector reveals the enzymatic mechanism of a novel acetyltransferase family. Nature Structure and Molecular Biology. 23: 847-852. (# co-first authors)
  7. Whitham S.A.*, Qi M., Innes R.W., Ma W., Lopes-Caitar V., Hewezi T. (2016) Molecular soybean-pathogen interactions. Annual Review in Phytopathology. 54: 443-468.
  8. Jing M. Guo B., Li H., Yang B. Wang H. Kong G. Zhao Y., Xu H., Wang Y., Ye W., Dong S., Qiao Y., Tyler B.M., Ma W., Wang Y*. (2016) A Phytophthora sojae effector suppresses endoplasmic reticulum stress-mediated immunity by stabilizing plant binging immunoglobulin proteins. Nature Communications. Doi: 10.1038/ncomms11685.
  9. Kuan T.#, Zhai Y.#, Ma W.* (2016) Small RNAs regulate plant responses to filamentous pathogens. Seminars in Cell and Developmental Biology. Doi: 10.1016/j.semcdb.2016.05.013.
  10. Ye W., Ma W.* (2016) Filamentous pathogen effectors interfering with small RNA silencing in plant hosts. Current Opinion in Microbiology. 32: 1-6.
  11. Ma K-W., Ma W.* (2016) Phytohormone pathways as targets of pathogens to facilitate infection. Plant Molecular Biology. 91: 713-725.
  12. Kong G., Zhao Y., Jing M., Huang J., Yang J., Xia Y., Kong L., Ye W., Xiong Q., Qiao Y., Dong S., Ma W., Wang Y. (2015) The Activation of Phytophthora Effector Avr3b by Plant Cyclophilin is Required for the Nudix Hydrolase Activity of Avr3b. PLoS Pathogens. 11(8): e1005139.  
  13. Ma K-W., Jiang S., Hawara E., Lee D.H., Pan S., Coaker G., Song J., Ma W.* (2015) Two serine residues in Pseudomonas syringae effector HopZ1a are required for acetyltransferase activity and association with the host co-factor. New Phytologist. doi: 10.1111/nph.13528. 
  14. Qiao Y., Shi J., Zhai Y., Hou Y., Ma W.* (2015) Phytophthora effector targets a novel regulator of small RNA pathway in plants to promote infection. Proc Natl Acad Sci USA.112: 5850-5855.
  15. Xiong Q.,Ye W.,Choi D., Wong J., Qiao Y., Tao K., Wang Y., Ma W. * (2014) Phytophthora Suppressor of RNA Silencing 2 is a Conserved RxLR Effector that Promotes Infection in Soybean and Arabidopsis thaliana. Mol Plant-Micro Interact. 27: 1379-1389.
  16. Wong J., Gao L., Yang Y., Zhai J., Arikit S., Yu Y., Duan S., Chan V., Xiong Q., Yan J., Li S., Liu R., Wang Y., Tang G., Meyers B.C., Chen X., Ma W.* (2014) Roles of Small RNAs in Soybean Defense against Phytophthora sojae Infection. The Plant J. 79: 928-940.
  17. Ma W. (2014) From Pathogen Recognition to plant immunity: BIK1 cROSses the divide. Cell Host & Microbe. 15: 253-254. 
  18. Shi J., Pagliaccia D., Morgan R.L., Qiao Y., Pan S., Vidalakis G., Ma, W.* (2014) Novel Diagnosis for citrus stubborn disease by detection of a Spiroplasma citri-secreted protein. Phytopathology. 104: 189-195.


    Jiang S., Yao J., Ma K-W., Zhou H., Song J., He S.Y., Ma W.* (2013) Bacterial effector activates jasmonate signaling by directly targeting JAZ transcriptional repressors. PLoS Pathogens. 9(10): e1003715. doi:10.1371/journal.ppat.1003715. 
  20. Qiao, Y., Liu, L., Xiong, Q., Flores, C., Wong, J., Shi, J., Wang, X., Liu, X., Xiang, Q., Jiang, S., Zhang, F., Wang, Y., Judelson, H.S., Chen, X., Ma, W.* (2013) Oomycete Pathogens Encode RNA Silencing Suppressors. Nature Genetics. 45: 330-333.
  21. Ma, K-W., Flores, C. and Ma, W.* (2011) Chromatin configuration as a battlefield in plant-bacteria interactions. Plant Phys.157: 535-543.
  22. Zhou, H., Lin, J., Johnson, A., Morgan, R.L., Zhong, W. and Ma, W.* (2011) Pseudomonas syringae type III effector HopZ1 targets a host enzyme to suppress isoflavone biosynthesis and promote infection in soybean. Cell Host & Microbe. 9, 177–186. (Preview at the same issue, Cell Host & Microbe 9: 169-170.)
  23. Lewis, J.D., Lee, A., Ma, W., Zhou, H., Guttman, D.S. and Desveaux, D. (2011) The YopJ superfamily in plant-associated bacteria. Mol. Plant Pathol. DOI: 10.1111/j.1364-3703.201.00719.x.
  24. Qiao, Y., Piao, R., Shi, J., Lee, S.I., Jiang, W., Kim, B.K., Lee, J., Han, L. Ma, W., and Koh, H.J. (2011) Fine mapping and candidate gene analysis of dense and erect panicle 3, DEP3, which confers high grain yield in rice (Oryza sativa L.). Theor Appl Genet. DOI: 10.1007/s00122-011-1543-6.
  25. Morgan, R.L., Zhou, H., Lehto, E., Nguyen, N., Bains, A., Wang, X. and Ma, W.* (2010) The catalytic domains of the diversified alleles of Pseudomonas syringae type III effector HopZ1 determine their distinct recognition specificities in plant hosts. Mol. Microbiol. 76: 437-455.
  26. Yang, Y., Zhao, J., Morgan, R.L., Ma, W.* and Jiang, T.* (2010) Computational prediction of type III secreted proteins from gram-negative bacteria. BMC Bioinformatics. Doi: 10.1186/1471-2105-11-SI-S47. (* co-corresponding authors).
  27. Zhou, H., Morgan, R.L., Guttman, D.S. and Ma, W.* (2009) Allelic variants of the Pseudomonas syringae type III effector HopZ1 are differentially recognized by plant resistance systems. Mol. Plant-Microbe Interact. 22: 176-189.
  28. Ma, W. and Guttman, D.S. (2008) Evolution of prokaryotic and eukaryotic virulence effectors. Curr Opin Plant Biol. Doi:10.1016/j.pbi.2008.05.001
  29. Ma, W., J.D. Lewis, D. Desveaux and D.S. Guttman. (2008) Evolution and Function of the Pseudomonas syringae HopZ Type III Effector Family. In: Biology of Plant-Microbe Interactions (Vol. 6). Edited by M. Lorito, S. L. Woo and F. Scala. ISBN 978-0-9654625-5-6.
  30. Lewis, J.D., Abada, W., Ma, W., Guttman, D.S. and Desveaux, D. (2008) The HopZ family of Pseudomonas syringae type III effectors requires myristoylation for virulence and avirulence functions in Arabidopsis. J. Bacteriol. 190: 2880-2891.
  31. Ma, W., Dong, F., Stavrinides, J. and Guttman, D.S. (2006) Type III effector diversification via both pathoadaptation and horizontal transfer in response to a coevolutionary arms race. PLoS Genetics. 2(12): e209.DOI.
  32. Stavrinides, J.*, Ma, W.* and Guttman, D.S. (2006) Terminal reassortment drives the quantum evolution of type III effectors in bacterial pathogens. PLoS Pathog. 2(10): e104.DOI.

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