PIN‐driven polar auxin transport in plant developmental plasticity: a key target for environmental and endogenous signals

Abstract

Contents 362I.362II.363III.366IV.369V.371VI.372373References373 Summary Plants master the art of coping with environmental challenges in two ways: on the one hand, through their extensive defense systems, and on the other, by their developmental plasticity. The plant hormone auxin plays an important role in a plant's adaptations to its surroundings, as it specifies organ orientation and positioning by regulating cell growth and division in response to internal and external signals. Important in auxin action is the family of PIN‐FORMED (PIN) auxin transport proteins that generate auxin maxima and minima by driving polar cell‐to‐cell transport of auxin through their asymmetric subcellular distribution. Here, we review how regulatory proteins, the cytoskeleton, and membrane trafficking affect PIN expression and localization. Transcriptional regulation of PIN genes alters protein abundance, provides tissue‐specific expression, and enables feedback based on auxin concentrations and crosstalk with other hormones. Post‐transcriptional modification, for example by PIN phosphorylation or ubiquitination, provides regulation through protein trafficking and degradation, changing the direction and quantity of the auxin flow. Several plant hormones affect PIN abundance, resulting in another means of crosstalk between auxin and these hormones. In conclusion, PIN proteins are instrumental in directing plant developmental responses to environmental and endogenous signals.

Transcription Factors in the Regulation of Somatic Embryogenesis

“…In addition to the postulated regulatory interactions with the auxin metabolism and signalling, the possible involvement of LEC2 in auxin polar transport cannot be ruled out as the upregulation of auxin efflux facilitators, PIN1 and PIN2, was observed in transgenic tobacco plants that overexpressed LEC2 (Guo et al 2013). PIN proteins are believed to direct plant developmental responses to environmental and endogenous signals through the control of the polar cell-to-cell transport of auxin (Habets and Offringa 2014), and relevantly, a key function of the auxin efflux carriers in ZE was documented (Friml et al 2003). The findings that the explants of a pin1 mutant were unable to undergo embryogenic induction in vitro (Su et al 2009) and that the inhibitors of the auxin polar transport severely impaired the embryogenic response of explants in different plants (Venkatesh et al 2009;Palovaara et al 2010) provided further support for the involvement of PINs in SE induction.…”

Root Bending Is Antagonistically Affected by Hypoxia and ERF-Mediated Transcription via Auxin Signaling

“…At the same time, the angle at which roots grew when exposed to hypoxia was exaggerated with auxin and NPA. NPA inhibits auxin flux primarily by inhibiting nonpolar ABCB19 auxin transporters and PIN-type auxin transporters, which results in a local increase in auxin concentration (Ottenschläger et al, 2003;Geisler et al, 2005;Nishimura et al, 2012;Habets and Offringa, 2014;Zhu et al, 2016). A synergistic effect of NPA and hypoxia and, to a lesser degree, of auxin and hypoxia was observed with regard to root bending, indicating that hypoxia and auxin signaling pathways interact.…”

“…Auxin efflux is mediated by the nonpolar ABCB carriers and by the polar auxin efflux carriers PIN1, PIN2, PIN3, PIN4, and PIN7 (Habets and Offringa, 2014). AUX1/ LAX carriers control auxin levels, while PINs control the direction of auxin transport within tissues (Band et al, 2014).…”

Phospholipid composition and a polybasic motif determine D6 PROTEIN KINASE polar association with the plasma membrane and tropic responses

“…Auxin levels within the plant are controlled by local auxin metabolism and directional auxin transport, which is achieved by the PIN-FORMED (PIN) efflux and the AUXIN RESISTANT 1/LIKE AUX1 (AUX1/ LAX) influx carriers (Adamowski and Friml, 2015). PINs are polarly distributed in the plasma membranes of many cells and their differential distribution results in the formation of local auxin maxima and minima that orchestrate the development of the growing plant body (Adamowski and Friml, 2015;Grunewald and Friml, 2010;Habets and Offringa, 2014).…”