Changes in phenylpropanoid metabolites associated with homology-dependent silencing of phenylalanine ammonia-lyase and its somatic reversion in tobacco

Gene silencing of phenylalanine ammonia-lyase (PAL) in transgenic tobacco (Nicotiana tabacum L.) is manifested phenotypically by reduced growth, altered leaf morphology, and reduced levels of phenylpropanoid compounds. Here we report the rare event of somatic reversion from silencing to PAL over-expression in tobacco harboring the bean PAL2 gene, This phenomenon allows the comparison of the effects of PAL under- and over-expression in the same plant. A comparison of gene silenced and revertant tissues reveals striking differences in lignin content and monomer composition, and both qualitative and quantitative differences in soluble and cell wall bound phenylpropanoid compounds in the recovered sector.