|Choi, Il Ryong|
Submitted to: Planta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/18/2006
Publication Date: 11/1/2006
Citation: Bailey, B.A., Bae, H., Strem, M.D., Roberts, D.P., Thomas, S.E., Samuels, G.J., Choi, I., Holmes, K.A. 2006. Fungal and plant gene expression during the colonization of theobroma cacao seedlings by isolates of four trichoderma species. Planta. 224(6):1449-1464. Interpretive Summary: Theobroma cacao (cacao), the source of cocoa, suffers from several major diseases and insect pests resulting in severe reductions in yield in many production areas. Cocoa is combined with United States agricultural commodities providing a direct benefit to the American farmer. Chemical and cultural control measures for cacao diseases are expensive to employ and are often ineffective. Biocontrol strategies, using beneficial organisms to control the damage caused by crop pests, are being developed for cacao diseases. As part of this work we are characterizing the interactions between biocontrol organisms and cacao using molecular tools with the goal of exploiting those molecular tools in optimizing biocontrol methods in the field. Subsets of cacao and fungal genes were identified that are expressed during the biocontrol organism/cacao interaction. The cacao genes were typical of genes expressed during drought stress and general plant defense while the biocontrol agents expressed genes required for growth within cacao tissues. The data suggests the biocontrol organisms are adapted to life within the cacao tree and may provide tolerance to drought stress as well as other stresses including plant diseases. The molecular tools developed will be used to estimate the population of biocontrol organisms in the field allowing optimization of biocontrol application strategies. By providing cacao farmers with sustainable, inexpensive biocontrol strategies for control of cacao diseases, cocoa supplies may be stabilized resulting in increased benefits to the cacao farmer, the cocoa industry, and the American farmer.
Technical Abstract: Endophytic isolates of Trichoderma species are being considered as agents for the control of diseases of Theobroma cacao (cacao), the source of chocolate. In order to exploit this potential we are studying the Trichoderma species/cacao endophytic interaction considering both plant and fungal gene expression. Total RNA was extracted from cacao seedlings colonized with four endophytic Trichoderma isolates representing four different species Differential display was used to identify 116 ESTs for genes responsive to endophytic colonization of cacao originating from cacao or Trichoderma for use in macroarray analysis. A subset of ESTs was used for real-time quantitative PCR (QPCR) with 19 primer sets for cacao ESTs and 16 primer sets for Trichoderma ESTs. The ESTs analyzed by QPCR were chosen based on results of the macroarray analysis or the ESTs putative identities. Seven plant derived ESTs were induced by colonization including putative genes for ornithine decarboxylase (P1), GST-like proteins (P4), zinc finger protein (P13), wound-induced protein (P26), and EF-calcium-binding protein (P29). Two plant derived ESTs (P12-extensin-like protein and P31-major intrinsic protein superfamily) were repressed by colonization with Trichoderma species. The combination of ESTs showing altered gene regulation was dependent on the Trichoderma isolate used. Similarly, the fungal ESTs detected as induced in colonized cacao seedlings were dependent on the Trichoderma isolate used. The most highly induced fungal genes were putative glucosyl hydrolase family 2 (F3), glucosyl hydrolase family 7 (F7), serine protease (F11), and alcohol oxidase (F19). The plant and fungal ESTs identified will be useful in further characterizing the Trichoderma species/cacao interaction and in developing biocontrol methods for cacao diseases.