Abstract
Root gravitropism allows plants to establish root systems and its regulation depends on polar auxin transport mediated by PIN-FORMED (PIN) auxin transporters. PINOID (PID) and PROTEIN PHOSPHATASE 2A (PP2A) act antagonistically on reversible phosphorylation of PINs. This regulates polar PIN distribution and auxin transport. Here we show that a peptidyl-prolyl cis/trans isomerase Pin1At regulates root gravitropism. Downregulation of Pin1At suppresses root agravitropic phenotypes of pp2aa and 35S:PID, while overexpression of Pin1At affects root gravitropic responses and enhances the pp2aa agravitropic phenotype. Pin1At also affects auxin transport and polar localization of PIN1 in stele cells, which is mediated by PID and PP2A. Furthermore, Pin1At catalyses the conformational change of the phosphorylated Ser/Thr-Pro motifs of PIN1. Thus, Pin1At mediates the conformational dynamics of PIN1 and affects PID- and PP2A-mediated regulation of PIN1 polar localization, which correlates with the regulation of root gravitropism.
Highlights
Root gravitropism allows plants to establish root systems and its regulation depends on polar auxin transport mediated by PIN-FORMED (PIN) auxin transporters
Our findings suggest that Pin1At catalyses the conformational dynamics of PIN1 and mediates the antagonistic effects of PID and PHOSPHATASE 2A (PP2A) on PIN1 polar localization, which correlates to regulation of root gravitropism
In the course of investigating the biological function of Pin1At22, we found that transgenic plants overexpressing Pin1At under the control of 35S promoter (35S:Pin1At) displayed an obvious agravitropic phenotype and slightly reduced root growth when they were germinated and grown on Murashige and Skoog (MS) agar plates oriented vertically for 4 days (Fig. 1a and Supplementary Fig. 1a,b)
Summary
Root gravitropism allows plants to establish root systems and its regulation depends on polar auxin transport mediated by PIN-FORMED (PIN) auxin transporters. Sequence and functional analyses have identified several conserved phosphorylation sites in the large central PIN hydrophilic loop, including three TPRXS(N/S) motifs and one Ser337/Thr[340] site[16,17] Reversible phosphorylation of those residues determines the polar PIN targeting and auxin-mediated plant development. We have shown that the only Arabidopsis orthologue of PIN1-type PPIases, Pin1At, regulates flowering time via phosphorylation-dependent isomerization of two MADS-box transcription factors[22] Another Arabidopsis PPIase, AtFKBP42 or TWISTED DWARF 1 that belongs to the subfamily of FKBP (FK506-binding protein)-type immunophilins, has been suggested to interact with PID, to affect auxin efflux mediated by an auxin exporter, ABC transporter B1 (refs 23,24). Our findings suggest that Pin1At catalyses the conformational dynamics of PIN1 and mediates the antagonistic effects of PID and PP2A on PIN1 polar localization, which correlates to regulation of root gravitropism
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