Practice question

PLETHORA genes are master regulators specifying embryonic root fate downstream of auxin accumulation. Loss-of-function plt1 plt2 double and higher order plt mutants produce seedlings completely lacking embryonic root pole despite presence of auxin maximum and basal polarity. Quiescent center marker WOX5 never induced, columella stem cells differentiate prematurely, basal pole converts to hypocotyl-like tissue showing reduced PIN expression and ectopic shoot reporters. Since PLTs also promote PIN transcription, their absence destabilizes auxin transport further reinforcing rootless phenotype, demonstrating absolute requirement of auxin-induced PLT effectors.