A Major Facilitator Superfamily Transporter Plays a Dual Role in Polar Auxin Transport and Drought Stress Tolerance inArabidopsis 

Abstract

Many key aspects of plant development are regulated by the polarized transport of the phytohormone auxin. Cellular auxin efflux, the rate-limiting step in this process, has been shown to rely on the coordinated action of PIN-formed (PIN) and B-type ATP binding cassette (ABCB) carriers. Here, we report that polar auxin transport in the Arabidopsis thaliana root also requires the action of a Major Facilitator Superfamily (MFS) transporter, Zinc-Induced Facilitator-Like 1 (ZIFL1). Sequencing, promoter-reporter, and fluorescent protein fusion experiments indicate that the full-length ZIFL1.1 protein and a truncated splice isoform, ZIFL1.3, localize to the tonoplast of root cells and the plasma membrane of leaf stomatal guard cells, respectively. Using reverse genetics, we show that the ZIFL1.1 transporter regulates various root auxin-related processes, while the ZIFL1.3 isoform mediates drought tolerance by regulating stomatal closure. Auxin transport and immunolocalization assays demonstrate that ZIFL1.1 indirectly modulates cellular auxin efflux during shootward auxin transport at the root tip, likely by regulating plasma membrane PIN2 abundance. Finally, heterologous expression in yeast revealed that ZIFL1.1 and ZIFL1.3 share H + -coupled K + transport activity. Thus, by determining the subcellular and tissue distribution of two isoforms, alternative splicing dictates a dual function for the ZIFL1 transporter. We propose that this MFS carrier regulates stomatal movements and polar auxin transport by modulating potassium and proton fluxes in Arabidopsis cells.

Cellular Auxin Homeostasis under High Temperature Is Regulated through a SORTING NEXIN1–Dependent Endosomal Trafficking Pathway

“…However, we do not completely rule out the possibility that an auxin-independent temperatureresponsive pathway may contribute partially to alter the root developmental processes. Recent studies have shown that different factors may participate in PIN2 stability, such as the Rho of Plants GTPase 6 (ROP6)/ROP-interactive CRIB motif-containing protein1 signaling pathway (Chen et al, 2012), the plant hormone gibberellic acid (Löfke et al, 2013), or a member of the Major Facilitator Superfamily transporters, Zinc-Induced Facilitator-Like 1 (Remy et al, 2013). Indeed, in the root tip, overexpression of ROP6 Root elongation and gravity response were measured as described in Figure 2.…”

Alternative Splicing at the Intersection of Biological Timing, Development, and Stress Responses

“…An interesting study has shown that AS of a Major Facilitator Superfamily transporter, ZINC-INDUCED FACILITATOR-LIKE1 (ZIFL1) leads to two protein isoforms, both of which function through modulating H + -coupled K + transport, but differ in tissue distribution and subcellular localization (Remy et al, 2013). The full-length ZIFL1.1 isoform is targeted to the vacuolar membrane of root cells.…”

“…The ZIFL1.3 transcript arises from selection of an alternative 39splice site located two nucleotides downstream of the authentic 39splice site, causing a frameshift mutation and introduction of a PTC that leads to the loss of the two last C-terminal membrane-spanning domains and localization of the truncated protein to the plasma membrane of leaf stomatal guard cells. Differential complementation of the zifl1 drought sensitivity and auxin-related defects shows that the full-length ZIFL1.1 protein influences cellular auxin efflux and polar auxin transport in roots, whereas the truncated ZIFL1.3 isoform regulates stomatal movement (Remy et al, 2013).…”

ABA signalling is fine-tuned by antagonistic HAB1 variants

“…Alternative splicing (AS) regulates not only transcript levels but also transcript isoforms, giving rise to proteins that differ in subcellular localization, stability and function [23][24][25] . More than 61% of intron-containing Arabidopsis genes undergo AS under normal conditions 26 .…”