Polarization of PIN3‐dependent auxin transport for hypocotyl gravitropic response in Arabidopsis thaliana

Abstract

SUMMARYGravitropism aligns plant growth with gravity. It involves gravity perception and the asymmetric distribution of the phytohormone auxin. Here we provide insights into the mechanism for hypocotyl gravitropic growth. We show that the Arabidopsis thaliana PIN3 auxin transporter is required for the asymmetric auxin distribution for the gravitropic response. Gravistimulation polarizes PIN3 to the bottom side of hypocotyl endodermal cells, which correlates with an increased auxin response at the lower hypocotyl side. Both PIN3 polarization and hypocotyl bending require the activity of the trafficking regulator GNOM and the protein kinase PINOID. Our data suggest that gravity-induced PIN3 polarization diverts the auxin flow to mediate the asymmetric distribution of auxin for gravitropic shoot bending.

Inactivation of Plasma Membrane–Localized CDPK-RELATED KINASE5 Decelerates PIN2 Exocytosis and Root Gravitropic Response inArabidopsis

“…Although PIN3, together with overlapping functions of PIN4 and 7, is thought to play an important role in statocyte sedimentation-induced switch in the polarity of columella-derived auxin flow (Friml et al, 2002), the pin3 mutant shows only weak gravitropic defects compared with the pin2 and aux1 mutants Swarup et al, 2005). This indicates that PIN2 and AUX1 play pivotal roles in the regulation of root gravitropic response, whereas in comparison, PIN3 is a key regulator of shoot gravitropic and phototropic responses in the stem endodermis (Ding et al, 2011;Rakusová et al, 2011).…”

The dynamics of plant plasma membrane proteins: PINs and beyond

“…Protein phosphorylation, acting interdependently with GNOM, has also been identified as a major determinant of PIN sorting. The activity of the AGC3-type serine/threonine protein kinase PINOID (PID) and that of its close relatives was shown to impact polar PIN distribution, promoting accumulation at apical/ shootward cellular plasma membrane domains in the case of PIN1 (Friml et al, 2004), whereas PIN3 distribution appears to shift from non-polar to lateral plasma membrane domains in endodermal cells (Ding et al, 2011;Rakusova et al, 2011). These sorting decisions are dependent on the phosphorylation status of PINs, as PINs encoded by mutant pin alleles mimicking constitutive phosphorylation were found to accumulate at apical domains, whereas those encoded by loss-of-phosphorylation alleles accumulated at basal domains, regardless of trans-acting PID activity Huang et al, 2010).…”

Auxin Polar Transport and Automorphosis in Plants

“…In the root columella, AtPIN3 is positioned symmetrically at the plasma membrane but rapidly relocalizes laterally on gravity stimulation . Gravistimulation has also been demonstrated to polarize AtPIN3 to the bottom side of hypocotyl endodermal cells, which correlates with an increased auxin response at the lower hypocotyl side (Rakusová et al, 2011). These facts mentioned above support an important role of PIN1 and PIN2 proteins as efflux transport of an anion form of IAA (IAA -) to out of cells in auxin polar transport as the process underlying differential auxin distribution in roots, and thereby regulating differential growth, while AtPIN3 proteins are suggested to play an important role in lateral auxin transport system by their predominant localization at the lateral side of endodermal cells .…”