Abstract
Main conclusion This study reveals that TRM21 acts as a positive regulator of flavonoid biosynthesis at the translational level in Arabidopsis , impacting both secondary metabolites and genes associated with root hair growth. Abstract TRM (TONNEAU1-recruiting motif) superfamily proteins are reported to be involved in microtubule assembly. However, the functions of this protein family are just beginning to be uncovered. Here, we provide metabolomic and genetic evidence that 1 of the 34 TRM members, TRM21 , positively regulates the biosynthesis of flavonoids at the translational level in Arabidopsis thaliana . A loss-of-function mutation in TRM21 led to root hair growth defects and stunted plant growth, accompanied by significant alterations in secondary metabolites, particularly a marked reduction in flavonoid content. Interestingly, our study revealed that the transcription levels of genes involved in the flavonoid biosynthesis pathway remained unchanged in the trm21 mutants, but there was a significant downregulation in the translation levels of certain genes [ flavanone 3-hydroxylase ( F3H ), dihydroflavonol-4-reductase ( DFR ), anthocyanidin reductase ( ANR ), flavanone 3’-hydroxylase ( F3'H ), flavonol synthase ( FLS ), chalcone synthase ( CHS )]. Additionally, the translation levels of some genes related to root hair growth [ RHO-related GTPases of plant 2 ( ROP2 ), root hair defective 6 ( RHD6 ), root hair defective 2 ( RHD2 )] were also reduced in the trm21 mutants. Taken together, these results indicate that TRM21 functions as a positive regulator of flavonoid biosynthesis at the translational level in Arabidopsis .