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Three genes belonging to the CYP98 family: CYP98A3, CYP98A8 and CYP98A9, have been reported in Arabidopsis thaliana. Analysis of mutants and expression analysis demonstrated the involvement of CYP98A3 in the synthesis of lignin monomers. As expected the CYP98A3 down-regulated lines showed altered lignin content and composition (H lignin instead of G/S lignin). These plants also exhibited a strikingly reduced size. The reasons for the changes in plant size and inhibition of development are analysed. This analysis indicated a direct impact of meta-hydroxylated phenolic precursors on cell growth. This analysis also revealed the existence of an alternative meta-hydroxylation pathway in A. thaliana. A role of meta-hydroxylated phenolic precursors in cell and plant growth is confirmed by the analysis of wild-type traitement with coumaroyl shikimate and caffeoyl shikimate and the analysis of overexpression of CYP98A3. We showed using promoter-GUS transformants that the CYP98A8 and CYP98A9 are expressed only in stamen in the young floral buds. CYP98A9 expression is also induced by biotic and abiotic stress.

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