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. 2010 Oct;154(2):458-62.
doi: 10.1104/pp.110.161380.

Endoplasmic reticulum: the rising compartment in auxin biology

Jirí Friml  1 , Angharad R Jones
Affiliations

Endoplasmic reticulum: the rising compartment in auxin biology

Jirí Friml et al. Plant Physiol. 2010 Oct.
No abstract available

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Figures

Figure 1.
Figure 1.
Schematic diagram of auxin fluxes and potential sites of auxin perception in the plant cell. The pH at the outer side of the PM is maintained at approximately 5.5 by the H+-ATPase activity of the PM (orange). As a consequence, a proportion of auxin (IAA) molecules in the apoplast remain protonated and can enter the cell via diffusion (wavy arrows). Auxin also enters cells through the action of specific uptake carriers of the AUX/LAX family (red). In the relatively higher pH of the cytoplasm, auxin molecules are deprotonated. The resulting ions cannot pass across the PM by diffusion and, instead, must be transported by efflux carriers including the PIN auxin transporters (green) and the MULTIDRUG RESISTANCE/P-GLYCOPROTEIN ABCB transporters (light blue). The coordinated polar localization of the auxin-efflux carriers from the long PIN subfamily at the PM determines the directionality of the auxin flow within the tissue. The long PIN proteins undergo constitutive endocytic recycling, which allows dynamic changes of PIN polarity by a transcytotic mechanism. PIN5, a member of the short PIN subfamily, is found at the membranes of the ER and leads to compartmentalization of auxin into the lumen of the ER. A number of auxin metabolic enzymes are also found in the lumen of the ER, and auxin metabolic profiling suggests that auxin entering the ER through PIN5-mediated transport rapidly undergoes metabolic conversion. The presumptive auxin receptor ABP1 (blue) is present both in the ER and in the apoplast. The receptor for the transcriptional auxin response pathway, TIR1 (light blue), is found in the nucleus. The different localizations of the long and short subfamilies of PIN efflux carriers, together with the spatial separation of the auxin receptors and localization of metabolic enzymes, implies that auxin signaling and metabolism, as well as auxin molecules themselves, are compartmentalized within the plant cell. Adapted from Křeček et al. (2009).
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