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 comparative genomic, functional genomic, genetic, biochemical and bioinformatic 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. We are working on the type III effectors of bacterial pathogens and the RxLR effectors of Phytophthora pathogens to understand their functions and evolution during the arms race with plant 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. We identified two alleles of HopZ1: the ancester-like allele HopZ1a, which triggers ETI in soybean and a newly evolved allele HopZ1b, which evades soybean recognition and at the same time retains the virulence function (Ma et al., PLoS Genetics, 2006; Morgan et al., Mol Microbiol. 2010). We further demonstrated that HopZ1 directly targets the isoflavonoid biosynthetic pathway in soybean in order to suppress defense (Zhou et al., Cell Host & Microbe, 2011). We are now in the process of characterize a HopZ1a-specific target of soybean, which potentially mediates HopZ1a-triggered immunity.  

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 serious problem worldwide; and Phytophthora sojae is the second most destructive pathogen of soybean that causes an average of 200 million dollars annual loss in the U.S. To date, battling Phytophthora diseases is challenged by a lack of understanding of pathogenesis.

Genome sequence analysis revealed hundreds of effector proteins from Phytophthora spp. The majority of these effectors contain a conserved N-terminal RxLR motif, which mediates their intake into host cells after being secreted from the pathogens through the specialized feeding structures, called haustoria. 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). RNA silencing is a universal gene regulation mechanism in eukaryotes. A central player in RNA silencing are 20-30 nucleotide (nt) small RNAs that guide the sequence-specific repression of target genes. Remarkably, these Phytophthora Suppressors of RNA silencing (PSRs) significantly promote infection, suggesting that inhibiting host RNA silencing pathways is an essential virulence strategy of these destructive pathogens. These findings revealed a new perspective in plant-eukaryotic pathogen interactions that involves small RNAs as integral players in the regulation of plant immunity. We are now investigating the direct targets of PSRs in order to understand the molecular basis of the virulence activity of PSRs.

Effectors as detection markers and molecular probes to understand Citrus diseases

In addition to basic research, we are enthusiastic in using our expertise on effectors to address industrial concerns. Citrus industry in the US is under major threats from the severe bacterial diseases, especially Huanglongbing (HLB). My group is interested in developing detection methods by monitoring the effectors secreted from the bacterial pathogens causing these diseases. We anticipated that these effectors could be dispersed through the plant transportation system and thus facilitating diagnosis. We have successfully developed a detection marker for the citrus stubborn disease. We are now using a similar approach to develop diagnostic tools for HLB.

Furthermore, we plan to use effectors as molecular probes to understand the pathogenesis of HLB and eventually develop sustainable management strategies against this destructive pathogen.


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. 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. In press.
  2. 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.
  3. 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.
  4. 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.
  5. 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.
  6. Ye W., Ma W.* (2016) Filamentous pathogen effectors interfering with small RNA silencing in plant hosts. Current Opinion in Microbiology. 32: 1-6.
  7. Ma K-W., Ma W.* (2016) Phytohormone pathways as targets of pathogens to facilitate infection. Plant Molecular Biology. 91: 713-725.
  8. 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.
  9. 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. 208: 1157-1168.
  10. 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.
  11. 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.
  12. 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.
  13. Ma W. 2014. From pathogen recognition to plant immunity: BIK1 cROSses the divide. Cell Host & Microbe. 15: 253-254.
  14. 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: 188-195.
  15. 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
  16. 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.
  17. Ma, K-W., Flores, C. and Ma, W.* 2011. Chromatin configuration as a battlefield in plant-bacteria interactions. Plant Physiol. 157: 535-543.
  18. 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.
  19. Qiao Y., Piao R., Shi J., Lee S.I., Jiang W., Kim B.K., Lee J., Han L., Ma W., 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. 122: 1439-1449.
  20. Morgan, R.L., Zhou, H., Lehto, E., Nguyen, N., Bains, A., Xiaoqiang Wang and Ma, W.* 2010. Catalytic domain of the diversified Pseudomonas syringae type III effector HopZ1 determines the allelic specificity in plant hosts. Mol Microbiol. 76: 437-455.
  21. 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)
  22. 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.
  23. Ma, W. and Guttman, D.S. 2008. Evolution of prokaryotic and eukaryotic virulence effectors. Curr Opin Plant Biol. 11: 412-419.
  24. Lewis, J.D., Abada, W., Ma, W., Guttman, D.S. and Desveaux, D. 2008. The HopZ family of Pseudomonas syringae type III effectors require myristoylation for virulence and avirulence functions in Arabidopsis. J. Bacteriol. 190: 2880-2891.
  25. Ma, W., Dong, F.F.T, 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.
  26. 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. (* co-first author)
  27. Ma, W., Charles, T.C. and Glick, B.R. 2004. Expression of an exogenous 1-aminocyclopropane-1-carboxylate deaminase gene in Sinorhizobium meliloti increases its ability to nodulate alfalfa. Appl. Environ. Micriobiol. 70: 5891-5897.
  28. Ma, W., Guinel, F.C. and Glick, B.R. 2003. Rhizobium leguminosarum bv. viciae 1-aminocyclopropane-1-carboxylate deaminase promotes nodulation of pea plants. Appl. Environ. Microbiol. 69: 4396-4402.
  29. Ma, W., Sebestianova, S., Sebestian, J., Burd, G.I., Guinel, F.C. and Glick, B.R. 2003. Prevalence of 1-aminocyclopropane-1-carboxylate deaminase in Rhizobia spp. Antonie van Leeuwenhoek 83: 285-291.
  30. Ma, W., Penrose, D.M. and Glick, B.R. 2002. The effect of ethylene on the nodulation of legumes. Can. J. Microbiol. 48: 947-954.
  31. Ma, W., Zalec, K. and Glick, B.R. 2001. Biological activity and colonization pattern of the bioluminescence labeled plant growth-promoting bacterium Kluyvera ascorbata SUD165/26. FEMS Microbiol Ecol. 35: 137-144.
  32. Zhang, J., Ma, W. and Tan, H. 2002. Cloning, expression and characterization of a gene encoding nitroalkane-oxidizing enzyme from Streptomyces ansochromogenes. Eur. J. Biochem. 269: 6302-6307.
  33. Glick, B.R., Penrose, D.M. and Ma, W. 2001. Bacterial promotion of plant growth. Biotechnol. Adv. 19: 135-138.

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