Downregulation of Brassica napus MYB69 ( BnMYB69 ) increases biomass growth and disease susceptibility via remodeling phytohormone, chlorophyll, shikimate and lignin levels.

MYB transcription factors are major actors regulating plant development and adaptability. is a staple oil crop and is hampered by lodging and diseases. Here, four () genes were cloned and functionally characterized. They were dominantly expressed in stems during lignification. RNA interference () plants showed considerable changes in morphology, anatomy, metabolism and gene expression. Stem diameter, leaves, roots and total biomass were distinctly larger, but plant height was significantly reduced. Contents of lignin, cellulose and protopectin in stems were significantly reduced, accompanied with decrease in bending resistance and resistance. Anatomical detection observed perturbation in vascular and fiber differentiation in stems, but promotion in parenchyma growth, accompanied with changes in cell size and cell number. In shoots, contents of IAA, shikimates and proanthocyanidin were reduced, while contents of ABA, BL and leaf chlorophyll were increased. qRT-PCR revealed changes in multiple pathways of primary and secondary metabolisms. IAA treatment could recover many phenotypes and metabolisms of plants. However, roots showed trends opposite to shoots in most cases, and phenotypes were light-sensitive. Conclusively, BnMYB69s might be light-regulated positive regulators of shikimates-related metabolisms, and exert profound influences on various internal and external plant traits.