Developmental expression of stress response genes in Theobroma cacao leaves and their response to Nep1 treatment and a compatible infection by Phytophthora megakarya

• Published in: Plant physiology and biochemistry 2005-06, Vol.43 (6), p.611-622
• Main Authors: Bailey, Bryan A., Bae, Hanhong, Strem, Mary D., Antúnez de Mayolo, Gabriela, Guiltinan, Mark J., Verica, Joseph A., Maximova, Siela N., Bowers, John H.
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Algal Proteins - genetics; Algal Proteins - physiology; Biological and medical sciences; Cacao; Cacao - growth & development; Cacao - metabolism; Classical and quantitative genetics. Population genetics. Molecular genetics; Developmental expression; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Plant; Generalities. Genetics. Plant material; Genes, Plant; Genetics and breeding of economic plants; Molecular genetics; Nep1; Phytophthora - metabolism; Phytophthora megakarya; Plant defense; Plant Diseases; Plant Leaves - growth & development; Plant Leaves - metabolism; Susceptibility; Theobroma cacao
• ISSN: 0981-9428; 1873-2690
• DOI: 10.1016/j.plaphy.2005.04.006

Developmental expression of stress response genes in Theobroma cacao leaves and their response to Nep1 and a compatible infection by Phytophthora megakarya were studied. Ten genes were selected to represent genes involved in defense ( TcCaf-1, TcGlu1,3, TcChiB, TcCou-1, and TcPer-1), gene regulation ( TcWRKY-1 and TcORFX-1), cell wall development ( TcCou-1, TcPer-1, and TcGlu-1), or energy production ( TcLhca-1 and TcrbcS). Leaf development was separated into unexpanded (UE), young red (YR), immature green (IG), and mature green (MG). Our data indicates that the constitutive defense mechanisms used by cacao leaves differ between different developmental stages. TcWRKY-1 and TcChiB were highly expressed in MG leaves, and TcPer-1, TcGlu-1, and TcCou-1 were highly expressed in YR leaves. TcGlu1,3 was highly expressed in UE and YR leaves, TcCaf-1 was highly expressed in UE leaves, and TcLhca-1 and TcrbcS were highly expressed in IG and MG leaves. NEP1 encodes the necrosis inducing protein Nep1 produced by Fusarium oxysporum and has orthologs in Phytophthora species. Nep1 caused cellular necrosis on MG leaves and young pods within 24 h of application. Necrosis was observed on YR leaves 10 days after treatment. Expression of TcWRKY-1, TcORFX-1, TcPer-1, and TcGlu-1 was enhanced and TcLhca-1 and TcrbcS were repressed in MG leaves after Nep1 treatment. Expression of TcWRKY-1 and TcORFX-1 was enhanced in YR leaves after Nep1 treatment. Infection of MG leaf disks by P. megakarya zoospores enhanced expression of TcGlu-1, TcWRKY-1, and TcPer-1 and repressed expression of TcChiB, TcLhca-1 and TcrbcS. Five of the six genes that were responsive to Nep1 were responsive to infection by P. megakarya. Susceptibility of T. cacao to P. megakarya includes altered plant gene expression and phytotoxic molecules like Nep1 may contribute to susceptibility.