In plants, the PIN proteins are

integral membrane protein An integral, or intrinsic, membrane protein (IMP) is a type of membrane protein that is permanently attached to the biological membrane. All ''transmembrane proteins'' are IMPs, but not all IMPs are transmembrane proteins. IMPs comprise a signi ...

s that transport the anionic form of the phytohormone

auxin Auxins (plural of auxin ) are a class of plant hormones (or plant-growth regulators) with some morphogen-like characteristics. Auxins play a cardinal role in coordination of many growth and behavioral processes in plant life cycles and are essenti ...

across membranes. Most of the PIN proteins (e.g. PIN1/2/3/4/7 in the model plant ''

Arabidopsis thaliana ''Arabidopsis thaliana'', the thale cress, mouse-ear cress or arabidopsis, is a small flowering plant native to Eurasia and Africa. ''A. thaliana'' is considered a weed; it is found along the shoulders of roads and in disturbed land. A winter a ...

'') localize at the plasma membrane (PM) where they serve as secondary active transporters involved in the efflux of auxin. The PM-localized PIN proteins show asymmetrical localisations on the membrane and are therefore responsible for

polar auxin transport Polar auxin transport is the regulated transport of the plant hormone auxin in plants. It is an active process, the hormone is transported in cell-to-cell manner and one of the main features of the transport is its asymmetry and directionality ( p ...

. Some other members of the PIN family (e.g. PIN5 and 8 in ''Arabidopsis'') localize mostly at the ER-membrane or have a dual PM and ER localisation (e.g. PIN6 in ''Arabidopsis''). These PIN proteins regulate the partitioning of auxin within the cell. The PM-localized PIN proteins physically interact with a few members of the large

PGP PGP or Pgp may refer to: Science and technology * P-glycoprotein, a type of protein * Pelvic girdle pain, a pregnancy discomfort * Personal Genome Project, to sequence genomes and medical records * Pretty Good Privacy, a computer program for the ...

family of transporters that also work as auxin efflux carriers (PGP1 and PGP19 in ''Arabidopsis''). These interactions result in a synergistic increase in auxin efflux. The activity and localization of the PM-localized PIN proteins is regulated by several

phosphorylation In chemistry, phosphorylation is the attachment of a phosphate group to a molecule or an ion. This process and its inverse, dephosphorylation, are common in biology and could be driven by natural selection. Text was copied from this source, wh ...

s on their large cytosolic hydrophilic loop carried out by kinases of the AGC family (e.g. PID, WAG1, WAG2, PID2 in ''Arabidopsis'') and the D6PK kinase.

References

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References

See also