Senthil Muthappa's Research Interests

Present research
         Plants are attacked by many disease causing organisms including, bacteria, fungi, viruses and nematodes. Billions of dollars are lost every year in crop production due to plant diseases. The control of plant disease is thus of fundamental importance to the modern agriculture.

Figure 1. Nonhost disease Resistance in N. benthamiana.  Artificial inoculation of nonhost bacterial phytopathogen Pseudomonas syringae pv. glycinea (PSG) in wild-type Nicotiana benthamiana lead to no bacterial growth and no disease symptoms. Whereas the host pathogen Pseudomonas syringae pv. tabaci (PST) effectively infected the leaf and produced disease. DPI, days post inoculation.

Figure 2.VIGS based screening to identify genes involved in nonhost disease resistance The host pathogen P. syringae pv. tabaci (Ps tab) was able to grow on both mock inoculated (TRV::00) and a gene silenced plant (TRV::19B2) leaves. The gene silenced plant clearly compromised its resistance for nonhost pathogens namely PSG, P. syringae pv. tomato T1 (Ps tom T1) and Xanthomonas campestris pv. vescatoria (XCV).

Figure 3. Agrobacterium-mediated transient co-expression of gene from tomato EIX responding locus LeEix2 and Trichoderma viride EIX (tvEIX) gene in the leaves of EIX non-responding species N. benthamiana produces HR.

Project I: Identification of plant genes involved in nonhost plant disease resistance
         Plants contain disease resistance genes (R) and protect themselves from disease-causing organisms by activating a broad array of defense responses that are still not fully understood. Even though several R genes have been identified, they confer resistance only to a particular strain of pathogen and hence in most cases the resistance conferred is not durable. Plants also resist majority of potential pathogens by less understood phenomenon called "nonhost resistance" (Fig. 1). Nonhost resistance can act against all races of a particular pathogen and can occur in all cultivars of a plant species. Dissecting the signal transduction pathway during nonhost resistance is a key to better understand this resistance mechanism and to develop, environmentally friendly, durable plant resistance against a broad range of pathogens.

          Our main objective is to identify the signaling components during nonhost disease resistance. In this project, virus-induced gene silencing (VIGS) is used as a functional genomics tool to do fast-forward genetics screening in N. benthamiana. We have a normalized N. benthamiana cDNA library in tobacco rattle virus (TRV)-based VIGS vector. In collaboration with another postdoc Dr. Keri Wang, we have performed VIGS based screening and identified putative candidate genes that compromise for nonhost disease resistance. Several bacterial pathogens for which N. benthamiana is a nonhost was tested in this screening (Fig. 2). The putative candidate genes identified are being further characterized through RNAi and overexpression studies in N. benthamiana and by analyzing the mutant collections in Arabidopsis.

Project II: Identification of plant genes involved in tvEIX-LeEIX mediated HR
          The molecular genetic analysis of the signal transduction pathway that modulates hypersensitive responses (HR) is an important step in understanding the induction of plant defense responses. An ethylene-inducing xylanase of Trichoderma viride (tvEIX) is a potent elicitor of plant defense responses, like HR, in specific cultivars of tobacco (N. tabacum) and tomato (Solanum lycopersicum). The genes that mediate tvEIX and LeEIX dependent activation of resistance mechanisms remain to be identified. One of our goals is to investigate the molecular mechanisms that allow plants to specifically activate defense responses after EIX treatment. We use VIGS-based high-throughput screen to identify genes that are required for the induction of tvEIX-LeEIX mediated HR (Fig. 3). This investigation will shed light on cellular processes and signaling components involved in induction of general plant defense against pathogens and will provide the basis for future biotechnological approaches to improve plant resistance to pathogens.

Previous research (Graduate program)
          My research work was started with small experiments during my under graduation (Agricultural Science). During this period I tested several newly released crop varieties and hybrids by Tamil Nadu Agricultural University (TNAU), Coimbatore and the experimental results and other in-house agricultural technologies were disseminated from lab to land through more than 35 popular research articles in several regional journals & radio talks. During my Masters program, I contributed to develop an empherical screening technique exploiting temperature induction response of crop plants. Later, temperature induction response (TIR) technique was developed for several different crop plants and as the outcome; we developed a thermotolerant sunflower hybrid. Adopting this technique thermotolerant lines in tomato was also developed and tested. During my PhD, I was involved in developing methods and approaches for testing transgenic plants engineered with abiotic stress responsive genes. Mainly in vitro methods to create oxidative/osmotic/salinity/temperature stress were developed. Further we developed protocols using virus-induced gene silencing (VIGS) approach to assess the functional relevance of drought-induced genes. I was also involved in developing stress screening protocols in Chlamydomonas reinharditii to assess the functional significance of abiotic stress genes. These findings are salient and important because they have direct practical significance in characterizing stress genes, testing transgenics & screening crop plants for stress tolerance. Supervisor - Prof. M. Udayakumar.

Publications
Senthil-Kumar, M, Gowda, H. V. R., Hema, R., Mysore, K. S., and Udayakumar, M. 2008b. Virus-induced gene silencing and its application in characterizing genes involved in abiotic stress tolerance. Journal of Plant Physiology, doi:10.1016/j.jplph.2008.04.007

Senthil-Kumar M, Anand A, Uppalapati SR and Mysore KS. 2008a. Virus-induced gene silencing and its applications. CAB Reviews: Perspectives in Agriculture, Veterinary Science, Nutrition and Natural Resources 3 (011), 18 pp. doi: 10.1079/PAVSNNR20083011

Senthil-Kumar M, Hema R, Anand A, Kang L, Udayakumar M and Mysore KS. 2007c. A systematic study to determine the extent of gene silencing in Nicotiana benthamiana and other Solanaceae species when heterologous gene sequences are used for virus-induced gene silencing. New Phytologist176, 782–791.

Hema R*, Senthil-Kumar M*, Shivakumar S, Chandrasekhara Reddy P and Udayakumar M. 2007. Chlamydomonas reinhardtii, a model system for functional validation of abiotic stress responsive genes. Planta 226, 655-670. (*equally contributed)

Senthil-Kumar M, Kumar G, Srikanthbabu V, Udayakumar M. 2007a. Assessment of variability in acquired thermotolerance: A potential option to study genotypic response and the relevance of stress genes. Journal of Plant Physiology 164: 111-125.

Senthil-Kumar M, Govind G, Kang L, Mysore KS, Udayakumar M. 2007b. Functional characterization of Nicotiana benthamiana homologs of peanut water deficit-induced genes by virus-induced gene silencing. Planta 225: 523-539.

Senthil-Kumar M, Udayakumar M. 2006. High throughput virus-induced gene silencing approach to assess the functional relevance of a moisture stress-induced cDNA homologous to lea4. Journal of Experimental Botany 57: 2291-2302.

Senthil-Kumar M, Udayakumar M. 2004. Development of thermotolerant tomato (Lycopersicon esculentum Mill.) lines: An approach based on mutagenesis. Journal of Plant Biology 31 (2): 139-148.

Senthil-Kumar M, Srikanthbabu V, Mohanraju B, Kumar G, Shivaprakash N, Udayakumar M. 2003. Screening of inbred lines to develop thermotolerant sunflower hybrid through temperature induction response (TIR) technique: A novel approach by exploiting residual variability. Journal of Experimental Botany 54: 2569-2578.