Recycling, clustering, and endocytosis jointly maintain PIN auxin carrier polarity at the plasma membrane

A combination of super-resolution microscopy in live cells and computational modeling provides new insights into the dynamic and interwoven mechanism that maintains the polar distribution of an important plant cargo

Subtalar Arthroereisis with the Vario Subtalar System® for treatment of the symptomatic, juvenile flatfoot - a radiological and clinical retrospective evaluation

Der retrospektive Vergleich von präoperativen und postoperativen Röntgenbildern des Fußes und Befragungen mit der AOFAS-Scale ergab eine signifikante Stellungsveränderung des Fußes und eine Beschwerdereduktion nach subtalarer Arthrorise mit dem Vario Subtalar System® bei 27 Patienten mit juvenilem Pes planovalgus.The retrospectice comparison of preoperative und postoperative x-ray pictures of the foot and the evaluation of a survey with the AOFAS-questonaire following the arthroereisis with the Vario Subtalar System® in 27 children with juvenile flatfeet showed a significant change of the foot from flatfoot deformity to plantigrade footposition and significantly reduced symptoms.2023-01-1

Differential degradation of PIN2 auxin efflux carrier by retromer-dependent vacuolar targeting

All eukaryotic cells present at the cell surface a specific set of plasma membrane proteins that modulate responses to internal and external cues and whose activity is also regulated by protein degradation. We characterized the lytic vacuole-dependent degradation of membrane proteins in Arabidopsis thaliana by means of in vivo visualization of vacuolar targeting combined with quantitative protein analysis. We show that the vacuolar targeting pathway is used by multiple cargos including PIN-FORMED (PIN) efflux carriers for the phytohormone auxin. In vivo visualization of PIN2 vacuolar targeting revealed its differential degradation in response to environmental signals, such as gravity. In contrast to polar PIN delivery to the basal plasma membrane, which depends on the vesicle trafficking regulator ARF-GEF GNOM, PIN sorting to the lytic vacuolar pathway requires additional brefeldin A-sensitive ARF-GEF activity. Furthermore, we identified putative retromer components SORTING NEXIN1 (SNX1) and VACUOLAR PROTEIN SORTING29 (VPS29) as important factors in this pathway and propose that the retromer complex acts to retrieve PIN proteins from a late/pre-vacuolar compartment back to the recycling pathways. Our data suggest that ARF GEF- and retromer-dependent processes regulate PIN sorting to the vacuole in an antagonistic manner and illustrate instrumentalization of this mechanism for fine-tuning the auxin fluxes during gravitropic response

PPP1, a plant-specific regulator of transcription controls Arabidopsis development and PIN expression

Directional transport of auxin is essential for plant development, with PIN auxin transport proteins representing an integral part of the machinery that controls hormone distribution. However, unlike the rapidly emerging framework of molecular determinants regulating PIN protein abundance and subcellular localization, insights into mechanisms controlling PIN transcription are still limited. Here we describe PIN2 PROMOTER BINDING PROTEIN 1 (PPP1), an evolutionary conserved plant-specific DNA binding protein that acts on transcription of PIN genes. Consistent with PPP1 DNA-binding activity, PPP1 reporter proteins are nuclear localized and analysis of PPP1 null alleles and knockdown lines indicated a function as a positive regulator of PIN expression. Furthermore, we show that ppp1 pleiotropic mutant phenotypes are partially reverted by PIN overexpression, and results are presented that underline a role of PPP1-PIN promoter interaction in PIN expression control. Collectively, our findings identify an elementary, thus far unknown, plant-specific DNA-binding protein required for post-embryonic plant development, in general, and correct expression of PIN genes, in particular.</p

Inositol Trisphosphate-Induced Ca2+ Signaling Modulates Auxin Transport and PIN Polarity

The phytohormone auxin is an important determinant of plant development. Directional auxin flow within tissues depends on polar localization of PIN auxin transporters. To explore regulation of PIN-mediated auxin transport, we screened for suppressors of PIN1 overexpression (supo) and identified an inositol polyphosphate 1-phosphatase mutant (supo1), with elevated inositol trisphosphate (InsP(3)) and cytosolic Ca2+ levels. Pharmacological and genetic increases in InsP(3) or Ca2+ levels also suppressed the PIN1 gain-of-function phenotypes and caused defects in basal PIN localization, auxin transport and auxin-mediated development. In contrast, the reductions in InsP(3) levels and Ca2+ signaling antagonized the effects of the supo1 mutation and disrupted preferentially apical PIN localization. InsP(3) and Ca2+ are evolutionarily conserved second messengers involved in various cellular functions, particularly stress responses. Our findings implicate them as modifiers of cell polarity and polar auxin transport, and highlight a potential integration point through which Ca2+ signaling-related stimuli could influence auxin-mediated development