The expression of phenylpropanoid andrelated genes was investigated in bm1, bm2, bm3, andbm4 near-isogenic maize plants at the 4–5 leaf stageusing a gene-speciWc cell wall macro-array. The bm3mutant, which is mutated in the caVeic acid O-methyltransferase(COMT) gene, exhibited the lowest numberof diVerentially expressed genes. Although noother phenylpropanoid gene had an altered expression,two distinct OMT and two cytochrome P450 geneswere overexpressed suggesting the activation of alternativehydroxylation/methylation pathways. The bm1mutant had the highest number of diVerentiallyexpressed genes, all of which were under-expressed.Bm1 mutant plants were aVected not only in cinnamylalcohol dehydrogenase (bm1 related CAD) geneexpression as expected, but also in the expression ofother CAD/SAD gene family members and severalregulatory genes including MYB, ARGONAUTE andHDZip. As originally believed, the bm1 mutationcould be localized at the CAD locus, but more probablyin a gene that regulates the expression of the CADgene family. The proWle of under-expressed genes inthe bm2 mutant is nearly similar to that of bm1. Thesegenes fell under several functional categories includingphenylpropanoid metabolism, transport and traYcking,transcription factors and regulatory genes. As thebm2 mutant exhibited a lower guaiacyl (G) unit lignincontent, the bm2 mutation could aVect a regulatorygene involved, perhaps indirectly, in the regulation,conjugation or transport of coniferaldehyde, or theestablishment of G-rich maize tissues. The pattern ofgene expression in bm4 plants, characterized by theover-expression of phenylpropanoid and methylationgenes, suggests that the bm4 mutation likely alsoaVects a gene involved in the regulation of lignification.