Regulation of polar auxin transport by protein and lipid kinases

Abstract

The directional transport of auxin, known as polar auxin transport (PAT), allows asymmetric distribution of this hormone in different cells and tissues. This system creates local auxin maxima, minima, and gradients that are instrumental in both organ initiation and shape determination. As such, PAT is crucial for all aspects of plant development but also for environmental interaction, notably in shaping plant architecture to its environment. Cell to cell auxin transport is mediated by a network of auxin carriers that are regulated at the transcriptional and post-translational levels. Here we review our current knowledge on some aspects of the 'non-genomic' regulation of auxin transport, placing an emphasis on how phosphorylation by protein and lipid kinases controls the polarity, intracellular trafficking, stability, and activity of auxin carriers. We describe the role of several AGC kinases, including PINOID, D6PK, and the blue light photoreceptor phot1, in phosphorylating auxin carriers from the PIN and ABCB families. We also highlight the function of some receptor-like kinases (RLKs) and two-component histidine kinase receptors in PAT, noting that there are probably RLKs involved in co-ordinating auxin distribution yet to be discovered. In addition, we describe the emerging role of phospholipid phosphorylation in polarity establishment and intracellular trafficking of PIN proteins. We outline these various phosphorylation mechanisms in the context of primary and lateral root development, leaf cell shape acquisition, as well as root gravitropism and shoot phototropism.

A lipid code-dependent phosphoswitch directs PIN-mediated auxin efflux in Arabidopsis development

“…These observations suggest that PDK1s are required for polar auxin transport, and the subsequent asymmetric auxin distribution, in which PIN auxin exporters play a critical role 3, 5 . Thus, we examined the polarity of PIN proteins firstly.…”

“…In addition to the role as membrane constituents, phospholipids also function as signals to transduce local membrane information to downstream effectors 47 . Both internal developmental signals and external environment cues have been reported to regulate membrane lipid dynamics, thereby modulating the downstream signal transduction 5, 45, 47, 48 . Multiple lines of genetic evidence suggest that the local membrane status regulates polar localization and recycling of PIN proteins.…”

“…The establishment and maintenance of local auxin minima, maxima and gradients rely on directional intercellular transport, which is mediated by a subset of auxin influx carriers AUXIN1 (AUX1)/LIKE AUX1s (LAXs) 1 , PIN (PIN-FORMED) efflux carriers 2, 3 and ABCB-type transporters 4 . It has been well documented that the activity and polar localization of PIN proteins are regulated by intracellular trafficking as well as post-translational modifications, including reversible phosphorylation 5 .…”

Rice siR109944 suppresses plant immunity to sheath blight and impacts multiple agronomic traits by affecting auxin homeostasis

“…Auxin is a major growth ‐ promoting hormone, although this phytohormone is co‐ordinately regulated in plant developmental processes (Jain et al , ; Teale et al , ; Mockaitis and Estelle, ). To some extent, the major research framework of auxin biosynthesis, homeostasis, transport, and signal transduction are conserved between different plant species (Valent and Khang, ; Ljung, ; Salehin et al , ; Armengot et al , ). For instance, miR393 not only affects multiple agronomic traits but also participates in immunity by inhibiting auxin signalling in Arabidopsis and rice (Si‐Ammour et al , ; Bian et al , ; Guo et al , ).…”

Seeing is better than believing: visualization of membrane transport in plants

“…An alternative approach might be imaging transporter regulation, such as by protein phosphorylation [16]. AGC kinases were shown to phosphorylate and thus alter transport activities of auxin transporters of the PIN and ABCB families [16][17][18][19][20], but have not yet been imaged in planta. A future alternative might be offered by novel GFP-based kinase reporters, called SPARK (Separation of Phases-based Activity Reporter of Kinase).…”