The conserved PFT1 tandem repeat is crucial for proper flowering in Arabidopsis thaliana

It is widely appreciated that short tandem repeat (STR) variation underlies substantial phenotypic variation in organisms. Some propose that the high mutation rates of STRs in functional genomic regions facilitate evolutionary adaptation. Despite their high mutation rate, some STRs show little to no variation in populations. One such STR occurs in the Arabidopsis thaliana gene PFT1 ( MED25 ), where it encodes an interrupted polyglutamine tract. Though the PFT1 STR is large (∼270 bp), and thus expected to be extremely variable, it shows only minuscule variation across A. thaliana strains. We hypothesized that the PFT1 STR is under selective constraint, due to previously undescribed roles in PFT1 function. We investigated this hypothesis using plants expressing transgenic PFT1 constructs with either an endogenous STR or with synthetic STRs of varying length. Transgenic plants carrying the endogenous PFT1 STR generally performed best across adult PFT1-dependent traits, in terms of complementing a pft1 null mutant. In stark contrast, transgenic plants carrying a PFT1 transgene lacking the STR entirely phenocopied a pft1 loss-of-function mutant for flowering time phenotypes, and were generally hypomorphic for other traits, establish...Continue Reading