Submitted to: Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/2/2005
Publication Date: 1/17/2005
Citation: Bailey, B.A., Strem, M.D., Antunez De Mayolo, G., Guiltinan, M.J. 2005. Gene expression in leaves of theobroma cacao in response to mechanical wounding, ethylene, or methyl jasmonate. Plant Science 128: 1247-1258.
Interpretive Summary: Theobroma cacao (cacao) is a tropical tree grown largely by small farmers around the world in tropical climates. There are several major diseases that threaten cacao production. Cacao production in South and Central America has been severely affected. We have characterized the responses of cacao to wounding and the plant hormones ethylene and methyl jasmonate, treatments known to induce resistance to disease in other plant species. One or more of these treatments induced differential expression of putative genes encoding a DNA binding protein, a protein regulating cell division, a Type III peroxidase, a endo-1,4-beta-glucanase, a class VII chitinase, a caffeine synthase, and a light harvesting complex protein. The knowledge gained concerning the expression of these genes, especially the methyl jasmonate induced genes, can be exploited in the development of cacao varieties with resistance to diverse plant pathogens. Varieties with resistance to diseases will allow sustainable production of cacao with reduced inputs assuring stable yields for farmers dependent upon the crop for their livelihood and assuring the supply required for dependent industries and associated consumers.
Technical Abstract: Theobroma cacao (cacao) yield is limited by disease and insect pests. Mechanical wounding, ethylene, and methyl jasmonate induce resistance to pests in many plant species. The effects of wounding, ethylene, and methyl jasmonate on gene expression in cacao seedlings were studied. Differential expression in response to one or more of these treatments was observed for putative genes encoding a DNA binding protein (TcWRKY-1), a protein regulating cell division (TcORFX-1), a Type III peroxidase (TcPer-1), a endo-1,4-beta-glucanases (TcGlu-1), a class VII chitinase (TcChiB), a caffeine synthase (TcCaf-1), and a light harvesting complex protein (TcLhca-1). TcWRKY-1 and TcORFX-1 were induced 0.25 h after wounding in young red (YR) and mature green (MG) leaves. Elevated TcPer-1 mRNA levels were detected 4 h after wounding in YR and MG leaves. Wounding induced enhanced expression of TcChiB in YR leaves. TcLhca-1 mRNA in MG leaves was reduced 48% by wounding (20 h). Ethylene (20 h) induced TcPer-1 in YR and MG leaves but induced TcGlu-1 in MG leaves only. Ethylene (20 h) repressed TcLhca-1 and TcCaf-1 in YR leaves. Ethylene repressed TcLhca-1 and TcChiB in MG leaves. Methyl jasmonate (20 h) induced TcCaf-1 and TcChiB in YR leaves and TcPer-1 and TcChiB in MG leaves. Ethylene/methyl jasmonate (4 h) induced TcPer-1 in YR and MG leaves. Ethylene/methyl jasmonate (20 h) induced TcChiB in YR leaves and TcGlu-1 in MG leaves. Expression of TcChiB in MG leaves and TcCaf-1 in YR leaves was repressed by ethylene/methyl (4 h). The response of cacao leaves to wounding, ethylene, or methyl jasmonate was influenced by the stage of leaf development. There was evidence of genetic crosstalk between the actions of ethylene and methyl jasmonate on gene expression in cacao leaves with both synergistic and antagonistic interactions being observed.