The Arabidopsis MYB5 and MYB23 transcription factors (TFs) regulate seed, trichome and root development through the formation of MYB-bHLH-WDR (MBW) complexes (Li et al., 2009; 2020, Allen et al., 2023). MYB5 and MYB23 function with partial redundancy to regulate leaf trichome expansion and branching. Arabidopsis leaf trichomes typically produce three to four branches while myb5/myb23 double mutant plants develop smaller rosette trichomes and more two-branched trichomes. Transcriptomic analysis performed on whole developing trichomes identified 577 differentially expressed genes, 62 of which were up-regulated and 515 down-regulated. PECTIN BIOSYNTHESIS ASSOCIATED1 (PBA1) was strongly down-regulated in myb5/myb23 trichomes and T-DNA insertion mutants in which PBA1 was non-functional failed to produce trichomes. Double and triple mutant analysis revealed a novel yet minor role for an additional MYB transcription factor in leaf trichome development and root cell elongation. Root length was reduced 20-30% in the double mutants. PBA1 expression was low in wild-type roots but was greatly increased (100-200 times that of wild-type) in the shorter double mutant roots. Consequently, PBA1 may have a different mode of regulation in roots compared to that in seeds and trichomes. Chromatin immunoprecipitation (ChIP) analysis found MYB5 directly binds the promoters of PBA1 and seven other cell wall biosynthesis genes involved in trichome differentiation and/or cell wall development. We propose a cell wall biosynthetic pathway containing genes differentially expressed in myb5/myb23 trichomes functionally assigned to pectin and/or cell wall polysaccharide biosynthesis. Models for MYB5 and MYB23-dependent regulation of gene expression in trichome, seed and root development are presented.