Abstract
The plant-specific proteins named PIN-FORMED (PIN) efflux carriers facilitate the direction of auxin flow and thus play a vital role in the establishment of local auxin maxima within plant tissues that subsequently guide plant ontogenesis. They are membrane integral proteins with two hydrophobic regions consisting of alpha-helices linked with a hydrophilic loop, which is usually longer for the plasma membrane-localized PINs. The hydrophilic loop harbors molecular cues important for the subcellular localization and thus auxin efflux function of those transporters. The three-dimensional structure of PIN has not been solved yet. However, there are scattered but substantial data concerning the functional characterization of amino acid strings that constitute these carriers. These sequences include motifs vital for vesicular trafficking, residues regulating membrane diffusion, cellular polar localization, and activity of PINs. Here, we summarize those bits of information striving to provide a reference to structural motifs that have been investigated experimentally hoping to stimulate the efforts toward unraveling of PIN structure-function connections.
Highlights
Auxin is an important regulator of plant development
PINs are integral membrane proteins and it has been experimentally verified that the Arabidopsis PINs 1–4 have 10 transmembrane domains (TMDs) grouped in two regions of five alpha helices separated with a large hydrophilic loop (HL) localized in the cytoplasm (Figure 1A; Nodzyński et al, 2016)
Alignment of the region spanning the tyrosine motif of all Arabidopsis PIN proteins revealed a conserved sequence NPN(S/T)YSSL in the HL of canonical PINs, but the last three SSL amino acids are missing in the short-looped PIN5 and PIN8
Summary
Auxin is an important regulator of plant development. This signaling molecule provides instructive cues through its accumulation patterns guiding the development from early embryogenesis (Robert et al, 2018) and throughout the entire plant ontogenesis (Vanneste and Friml, 2009), orchestrating the establishment of embryonic apical-basal polarity (Friml et al, 2003), root patterning (Friml et al, 2002a; Ditengou et al, 2008), root system architecture (Lavenus et al, 2016), organogenesis and organ positioning (Heisler et al, 2005; Pahari et al, 2014), and cell differentiation (Marhava et al, 2018). PINs are integral membrane proteins and it has been experimentally verified that the Arabidopsis PINs 1–4 have 10 TMDs grouped in two regions of five alpha helices separated with a large hydrophilic loop (HL) localized in the cytoplasm (Figure 1A; Nodzyński et al, 2016).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
