Post-transcriptional regulation of auxin transport proteins: cellular trafficking, protein phosphorylation, protein maturation, ubiquitination, and membrane composition

Abstract

Auxin concentration gradients, established by polar transport of auxin, are essential for the establishment and maintenance of polar growth and morphological patterning. Three families of cellular transport proteins, PIN-formed (PIN), P-glycoprotein (ABCB/PGP), and AUXIN RESISTANT 1/LIKE AUX1 (AUX1/LAX), can independently and co-ordinately transport auxin in plants. Regulation of these proteins involves intricate and co-ordinated cellular processes, including protein-protein interactions, vesicular trafficking, protein phosphorylation, ubiquitination, and stabilization of the transporter complexes on the plasma membrane.

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

“…PM localization domains of CRK5 thus partially overlap in different root cell types with those of examined PINs (Figures 3 and 7; see Supplemental Figures 6 to 8 online). In the epidermis, CRK5 localization closely resembles that of the boron efflux transporter BOR4 (Miwa et al, 2007) but clearly differs from those of ABCB/PGP1, 4, and 19 auxin transporters, which appear to selectively modulate the activities of specific PINs (Geisler et al, 2005;Terasaka et al, 2005;Titapiwatanakun and Murphy, 2009). Similarly, the cell typespecific polar localization of CRK5 also completely differs from that of AUX1 (see Supplemental Figure 9 online), which appears to act independently of so far studied ABCB/PGPs .…”

“…By contrast, the pgp4 mutation impairs both acro-and basipetal auxin transport only in lateral roots without affecting the elongation and gravitropic response of primary root . Despite these apparently contradictory observations, based on the finding that some ABCB/PGPs, such as PGP1 (Henrichs et al, 2012), are phosphorylated by the AGC PIN kinase PID, it will be interesting to determine whether CRK5 or other members of the Arabidopsis CRK family contribute by phosphorylation to the modulation of regulatory interactions between ABCB/PGPs and PINs (Bandyopadhyay et al, 2007;Titapiwatanakun and Murphy, 2009). Definition of the role of CRK5 in the regulation of root gravitropic response now opens the way to answer these important questions by combined genetic analysis of members of the CRK family.…”

“…As hypothesized originally by Colodny and Went (Went, 1974), in response to altered gravity stimulus, auxin is transported from upper to lower sections of bending organs stimulating differential cell elongation responses. Cellular transport of auxin is controlled by the AUX/LAX influx and PIN-FORMED (PIN) efflux carriers, and the PGP/ABCB (for P-glycoprotein/ATP binding cassette protein subfamily B) transporters, several of which function in conjunction with PINs (reviewed in Kramer, 2004;Bandyopadhyay et al, 2007;Titapiwatanakun and Murphy, 2009). Whereas regulation of polar localization, activity, and stability of auxin carriers and transporters is being deciphered in detail (Friml, 2010;Ganguly et al, 2012), it is less clear how primary sensing of gravity is linked to specific switches in polar auxin transport.…”

Master and servant: Regulation of auxin transporters by FKBPs and cyclophilins

“…Channels, in contrast, when open let ions diffuse rapidly down electrical and concentration gradients resulting in detectable currents. ABCBs were clearly shown to utilize ATP as a direct energy source and to transport auxin steadily across cellular membranes, suggesting ABCBs act in most cases as primary auxin pumps [4,6,127]. PINs and AUX1/LAXs are thought to act as secondary active auxin exporters dependent on an electrochemical gradient.…”

Plasma membrane protein ubiquitylation and degradation as determinants of positional growth in plants

“…Given their essential role in crosstalk between organism and environment, it is not too surprising that several regulatory pathways are required for a tight control of PM proteins (Geldner and Robatzek 2008;Chen et al 2011;Ganguly et al 2012;Guerra and Callis 2012;Robinson et al 2012). Specifically control of localization and steady-state protein levels play an essential role in the regulation of PM protein function (Titapiwatanakun and Murphy 2009;Lofke et al 2013a). However, while research in (Corresponding author) animals and fungi has revealed a complex machinery of cis-and trans-acting determinants, regulation of plant PM protein localization and turnover is still less understood (Murphy et al 2005;Schellmann and Pimpl 2009;Zarsky and Potocky 2010;Reyes et al 2011).…”