Polar transport of the
phytohormone auxin controls numerous growth responses in plants. Molecular characterization of
auxin transport in
Arabidopsis thaliana has provided important insights into the mechanisms underlying the regulation of
auxin distribution. In particular, the control of
subcellular localization and expression of PIN-type
auxin efflux components appears to be fundamental for orchestrated distribution of the
growth regulator throughout the entire plant body. Here we describe the identification of two Arabidopsis loci, MOP2 and MOP3 (for MODULATOR OF PIN), that are involved in control of the steady-state levels of PIN protein.
Mutations in both loci result in defects in
auxin distribution and
polar auxin transport, and cause
phenotypes consistent with a reduction of PIN protein levels.
Genetic interaction between PIN2 and both MOP loci is suggestive of functional cross-talk, which is further substantiated by findings demonstrating that
ectopic PIN up-regulation is compensated in the mop background. Thus, in addition to pathways that control PIN localization and transcription, MOP2 and MOP3 appear to be involved in fine-tuning of
auxin distribution via
post-transcriptional regulation of PIN expression.
