The PIN-LIKES (PILS) are known to be involved in regulating the intracellular auxin homeostasis, accumulation and regulating nuclear auxin signaling. They are located in the Endoplasmic Reticulum Envelop and differ from PINs (PIN1, PIN2, PIN3, PIN4, PIN7) involved in the intercellular polar auxin transport by having a shorter non-memebrane integrated loop in their protein structure, similar to ER located PINs (PIN5, PIN6 and PIN8).
Not much is known about the direction of auxin flow mediated by the PILS. However to aid display of gene products on the ER membrane, we added the direction of flow of auxin transport, based on the observation that they help in increasing the free auxin amount in the cytoplasm.
PIN family proteins that are mainly involved in the intercellular autin transport via the Auxin Polar Transport pathway mediated by the PIN proteins located on the plasmamembrane. However, the Arabidopsis PIN family members PIN5, PIN6 and PIN8 are known for their location on the endoplasmic reticulum membrane/envelope. PIN6 is also likely co-located with the nuclear membrane. According to Sawchuk MG et al. (2013) PIN5, PIN6 and PIN8 play roles in leaf vein patterning. PIN5 and PIN8 play an antagonistic role in regulating the intercellular auxin transport as well as in gametophyte (pollen) and sporophyte development. This pathway in rice was created to based on the homology to Arabidopsis genes. The gene homology predictions did not find the reciprocal best match to PIN6. PILS genes were added to the pathway based on their role in auxin homeostasis and ER envelope localization. The pathway also includes vacuolar memebrane localized WAT1 homolog that facilitates auxin efflux from vacuole to cytosol and regulates cell wall thickening. The ER localized PIN6 and PIN8 along with PINs localized in the plasmamemebrane that carryout polar auxin intercellular transport regulate leaf vein patterning.
