[3] Most of the PIN proteins (e.g. PIN1/2/3/4/7 in the model plant Arabidopsis thaliana) localize at the plasma membrane (PM) where they serve as secondary active transporters involved in the efflux of auxin.
The PM-localized PIN proteins physically interact with a few members of the large PGP family of transporters that also work as auxin efflux carriers (PGP1 and PGP19 in Arabidopsis).
Interestingly, PIN clusters don't align with REMORIN 1.2 but are affected by elevated salicylic acid levels or REM1.2, which induce hyperclustering of PIN2, influencing auxin distribution.
[6] Moreover, connections between the plasma membrane, cell wall, and the composition of molecules like pectin and cellulose influence PIN clustering, impacting auxin transport.
Auxin induces a complex transcriptional mechanism that regulates many genes but also causes a fast, non-transcriptional response, targeting proteins like Myosin XI and its adaptor MadB2.