Antisense and sense expression of cDNA coding for CYP73A15, a class II cinnamate 4-hydroxylase, leads to a delayed and reduced production of lignin in tobacco

A number of plant species contain the class II of genes encoding the cytoch rome P450, CYP73, the cognate protein of which cinnamic acid 4-hydroxylase, is the second enzyme of the phenylpropanoid pathway. In order Co begin to determine possible functionality, tobacco has been transformed with a trunc ated French bean class II cinnamate hydroxylase (CYP73A15) in the sense and antisense orientations. Signals for C4H protein could be detected in vascu lar tissue from wild-type plants using heterologous probes. The transformed plants showed a normal phenotype, even though detectable C4H protein was m uch reduced in tissue prints. Young propagated transformants displayed a ra nge of reduced C4H activities, as well as either reduced or no phloroglucin ol-stainable lignin. However, all mature tobacco plants showed the accumula tion of lignin, even though its deposition was apparently delayed. This was not due to induction of tyrosine ammonia-lyase activity, which was not det ected, but instead it is presumed due to sufficient C4H residual activity. Analysis of the lignin content of the plants showed reductions of up to 30% with a slightly reduced syringyl to guaiacyl ratio as compared to wild typ e. This reduction level was favourable in comparison with some other target s in the lignification pathway that have been manipulated including that of class I cinnamate 4-hydroxylase. It is proposed that the class Il cinnamat e 4-hydroxylase might also function in lignification in a number of species including French bean and tobacco, based on these data. (C) 2001 Elsevier Science Ltd. All rights reserved.