Developmental phenotypes of plants expressing phosphovariants of .

The transcription factor Myeloblastosis protein 75 (MYB75, AT1G56650) is a well-established transcriptional activator of genes required for anthocyanin and flavonoid production, and a repressor of lignin and other secondary cell wall biosynthesis genes. MYB75 is itself tightly regulated at the transcriptional, translational and post-translational levels, including protein phosphorylation by MAP kinases Examination of the behavior of different phosphovariant versions of MYB75 and revealed that overexpression of the MYB75 phosphovariant had a particularly marked effect on global changes in gene expression suggesting that phosphorylated MYB75 could be involved in a broader range of functions than previously recognized. Here, we describe a range of distinct developmental phenotypes observed among lines expressing various phosphovariant forms of MYB75. Expression of either or phosphovariants, from the endogenous promoter, in mutants (Nossen background), resulted in severely impaired germination rates, and developmental arrest at early seedling stages. plants overexpressing from a strong constitutive Cauliflower mosaic virus (CaMV35S) promoter displayed slower development, with delayed bolting, flowering and onset of senescence. Conversely, -overexpressing lines flowered and set seed earlier than either Col-0 WT controls or other -overexpressors ( and ). Histochemical analysis of mature stems also revealed ectopic vessel development in plants overexpressing ; this phenotype was particularly prominent in the phosphovariant. These data suggest that MYB75 plays a significant role in plant development, and that this aspect of MYB75 function is influenced by its phosphorylation status.