Mechanisms of tomato basal resistance to fungal infection
Abstract
Tomato (Solanum lycopersicum) is one of the most important fruit vegetables cultivated across the world. It is the second largest consumed vegetables in the world next to potato. However, cultivated tomato is susceptible to many diseases including those caused by the necrotrophic fungi Botrytis cinerea and Alternaria solani. We studied response of wild and cultivated Solanum spp. to gray mold and early blight diseases to identify wild Solanum species with increased resistance to the pathogens, identify and characterize genes involved in resistance response, and further characterize selected genes using virus induced gene silencing (VIGS) and RNA interference (RNAi). Seven wild Solanum spp. and three cultivated tomato varieties were evaluated for their resistance to B. cinerea and A. solani. Statistical analysis of disease lesion size using General Linear Model (SAS) showed statistically significant (P<0.001) differences between genotypes. S. lycopersicoides was the most resistant with broad spectrum resistance to both pathogens suggesting its potential use as sources of broad spectrum disease resistance in tomato improvement. RNA-Seq analysis of S. lycopersicoides genes during interaction with B. cinerea showed that about thirteen percent the total assembled S. lycopersicoides unigenes in infected plant (24 and 48hpi) compared with un-infected base line (0 hpi) were differentially expressed. K-means cluster analysis showed four distinct clusters out of which clusters 1-3 include up-regulated defense and stress response genes while genes in cluster 4 were down-regulated. Genes involved in primary metabolism and photosynthesis was included in cluster 4. The data show that the mechanism of S. lycopersicoides resistance to Botrytis involves transcriptional reprogramming: upregulation of defense and stress response genes while downregulating photosynthesis and primary metabolism. Virus induced gene silencing (VIGS) of 18 tomato genes, mainly protein kinases, identified four genes whose significant reduction of their transcript correlates with increased susceptibility. Further characterization of the biological function of one of the selected genes TPK1b related kinase 1 (TRK1) using transgenic TRK1-RNAi lines revealed significant increases in susceptibility due to suppression of the transcript of TRK1 suggesting the involvement of this gene in tomato basal resistance to Botrytis. Moreover, TRK1-RNAi lines are compromised in Botrytis induced expression of ethylene/jasmonic acid induced defense genes such as proteinase inhibitor I (PI-I) and allene oxide synthase (SlAOS ). Finally, we show that TRK1 encodes an active kinase, with both autophosphorylation and transphosphorylation activity, and it localizes to the plasma membrane.
Degree
Ph.D.
Advisors
Mengiste, Purdue University.
Subject Area
Plant Pathology
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