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Phenolic compounds are essential components of the defensive chemical arsenal of conifer trees. This chemically diverse group encompasses stilbenoids, flavonoids, isoflavonoids, proanthocyanidins and lignans. All of them are produced from the common precursors, CoA esters of the phenylpropanoids: p-coumaroyl-CoA, cinnamoyl-CoA, caffeoyl-CoA and feruloyl-CoA. Two classes of enzymes, stilbene synthases and chalcone synthases, play important roles in the biosynthesis of plant phenolics, such as the conversion of the phenylpropanoid-CoA esters into stilbenoids and flavonoids, respectively. In this study, we investigated the transcriptional responses of the Scots pine ( Pinus sylvestris) genes encoding stilbene and chalcone synthases to the infection by the fungal pathogen Heterobasidion annosum. The experiments were performed on pine seedlings and mature trees. Our results show that the stilbene synthase gene is strongly induced in both age groups, but the level of induction in adult trees varied considerably among individual trees. Systemic induction in needles and hypocotyl regions was documented in young seedlings following fungal inoculation in root region. Concurrent changes in the expression of the chalcone synthase gene in response to fungal infection were much less pronounced. Our data confirm previous observations on the differential regulation of these enzymes in Scots pine and emphasize the role of stilbene synthase in the induced response to fungal infection. [ABSTRACT FROM AUTHOR]

Gene expression levels of pathogenesis-related proteins ( PR1, PR3, PR5, PR8 and PR9), cell wall modification genes ( PAL and expansin), signal transduction genes ( ACC oxidase, AOC, MAPK) and a Myb transcription factor were compared in two Hevea brasiliensis budded clones ( RRIM612 and PR107) 5 weeks after wounding and artificial inoculation with the white rot fungus, Rigidoporus microporus. PR3 class I chitinase was upregulated in RRIM612 in response to the pathogen when compared with the wounded control. PR9 class IV peroxidase was highly upregulated in PR107. PR1 and PR8 were expressed more in wounded than in inoculated clones. Genes involved in ethylene and jasmonic acid signalling pathways and phenylalanine ammonia-lyase ( PAL) were upregulated almost equally in both clones. The Myb transcription factor was upregulated in RRIM612, while MAPK was upregulated in PR107 when compared to the wounded control. The predicted expansin-like protein was upregulated 40-fold in RRIM612 when compared to the wounded control. The results demonstrate the variability in defence responses in different clones and provide the first set of defence genes expression profiles in the host-pathogen interaction of the white rot disease of rubber trees. [ABSTRACT FROM AUTHOR]