Arabidopsis PIN2 protein directs transport of the phytohormone auxin from the root tip into the root elongation zone. Variation in hormone transport, which depends on a delicate interplay between PIN2 sorting to and from polar plasma membrane domains, determines root growth. By employing a constitutively degraded version of PIN2, we identify brassinolides as antagonists of PIN2 endocytosis. This response does not require de novo protein synthesis, but involves early events in canonical brassinolide signaling. Brassinolide-controlled adjustments in PIN2 sorting and intracellular distribution governs formation of a lateral PIN2 gradient in gravistimulated roots, coinciding with adjustments in auxin signaling and directional root growth. Strikingly, simulations indicate that PIN2 gradient formation is no prerequisite for root bending but rather dampens asymmetric auxin flow and signaling. Crosstalk between brassinolide signaling and endocytic PIN2 sorting, thus, appears essential for determining the rate of gravity-induced root curvature via attenuation of differential cell elongation.
- MeSH
- Arabidopsis účinky léků metabolismus MeSH
- biologický transport účinky léků MeSH
- brassinosteroidy metabolismus farmakologie MeSH
- endocytóza účinky léků MeSH
- gravitropismus účinky léků fyziologie MeSH
- kořeny rostlin účinky léků metabolismus MeSH
- kyseliny indoloctové metabolismus MeSH
- meristém účinky léků metabolismus MeSH
- proteiny huseníčku metabolismus MeSH
- regulátory růstu rostlin metabolismus farmakologie MeSH
- signální transdukce MeSH
- steroidy heterocyklické metabolismus farmakologie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Directional organ growth allows the plant root system to strategically cover its surroundings. Intercellular auxin transport is aligned with the gravity vector in the primary root tips, facilitating downward organ bending at the lower root flank. Here we show that cytokinin signaling functions as a lateral root specific anti-gravitropic component, promoting the radial distribution of the root system. We performed a genome-wide association study and reveal that signal peptide processing of Cytokinin Oxidase 2 (CKX2) affects its enzymatic activity and, thereby, determines the degradation of cytokinins in natural Arabidopsis thaliana accessions. Cytokinin signaling interferes with growth at the upper lateral root flank and thereby prevents downward bending. Our interdisciplinary approach proposes that two phytohormonal cues at opposite organ flanks counterbalance each other's negative impact on growth, suppressing organ growth towards gravity and allow for radial expansion of the root system.
- MeSH
- Arabidopsis fyziologie MeSH
- celogenomová asociační studie MeSH
- cytokininy metabolismus MeSH
- geneticky modifikované rostliny fyziologie MeSH
- genom rostlinný genetika MeSH
- gravitropismus MeSH
- kořeny rostlin metabolismus MeSH
- oxidoreduktasy genetika metabolismus MeSH
- proteiny huseníčku metabolismus MeSH
- proteolýza MeSH
- regulátory růstu rostlin metabolismus MeSH
- systémová biologie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
distribution of auxin within plant tissues is of great importance for developmental plasticity, including root gravitropic growth. Auxin flow is directed by the subcellular polar distribution and dynamic relocalisation of auxin transporters such as the PIN-FORMED (PIN) efflux carriers, which can be influenced by the main natural plant auxin indole-3-acetic acid (IAA). Anthranilic acid (AA) is an important early precursor of IAA and previously published studies with AA analogues have suggested that AA may also regulate PIN localisation. Using Arabidopsis thaliana as a model species, we studied an AA-deficient mutant displaying agravitropic root growth, treated seedlings with AA and AA analogues and transformed lines to over-produce AA while inhibiting its conversion to downstream IAA precursors. We showed that AA rescues root gravitropic growth in the AA-deficient mutant at concentrations that do not rescue IAA levels. Overproduction of AA affects root gravitropism without affecting IAA levels. Treatments with, or deficiency in, AA result in defects in PIN polarity and gravistimulus-induced PIN relocalisation in root cells. Our results revealed a previously unknown role for AA in the regulation of PIN subcellular localisation and dynamics involved in root gravitropism, which is independent of its better known role in IAA biosynthesis.
- MeSH
- Arabidopsis účinky léků metabolismus MeSH
- chinolony farmakologie MeSH
- gravitropismus fyziologie MeSH
- kořeny rostlin anatomie a histologie účinky léků růst a vývoj fyziologie MeSH
- kyseliny indoloctové chemie metabolismus MeSH
- mutace genetika MeSH
- ortoaminobenzoáty chemie metabolismus farmakologie MeSH
- polarita buněk * účinky léků MeSH
- proteiny huseníčku metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Polar auxin transport plays a pivotal role in plant growth and development. PIN-FORMED (PIN) auxin efflux carriers regulate directional auxin movement by establishing local auxin maxima, minima, and gradients that drive multiple developmental processes and responses to environmental signals. Auxin has been proposed to modulate its own transport by regulating subcellular PIN trafficking via processes such as clathrin-mediated PIN endocytosis and constitutive recycling. Here, we further investigated the mechanisms by which auxin affects PIN trafficking by screening auxin analogs and identified pinstatic acid (PISA) as a positive modulator of polar auxin transport in Arabidopsis (Arabidopsis thaliana). PISA had an auxin-like effect on hypocotyl elongation and adventitious root formation via positive regulation of auxin transport. PISA did not activate SCFTIR1/AFB signaling and yet induced PIN accumulation at the cell surface by inhibiting PIN internalization from the plasma membrane. This work demonstrates PISA to be a promising chemical tool to dissect the regulatory mechanisms behind subcellular PIN trafficking and auxin transport.
- MeSH
- Arabidopsis účinky léků metabolismus MeSH
- biologický transport účinky léků MeSH
- buněčná membrána účinky léků metabolismus MeSH
- endocytóza * účinky léků MeSH
- fenotyp MeSH
- fenylacetáty farmakologie MeSH
- gravitropismus účinky léků MeSH
- hypokotyl účinky léků růst a vývoj MeSH
- kořeny rostlin účinky léků růst a vývoj MeSH
- kyseliny indoloctové metabolismus MeSH
- proteiny huseníčku metabolismus MeSH
- signální transdukce MeSH
- výhonky rostlin metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Intercellular distribution of the plant hormone auxin largely depends on the polar subcellular distribution of the plasma membrane PIN-FORMED (PIN) auxin transporters. PIN polarity switches in response to different developmental and environmental signals have been shown to redirect auxin fluxes mediating certain developmental responses. PIN phosphorylation at different sites and by different kinases is crucial for PIN function. Here we investigate the role of PIN phosphorylation during gravitropic response. Loss- and gain-of-function mutants in PINOID and related kinases but not in D6PK kinase as well as mutations mimicking constitutive dephosphorylated or phosphorylated status of two clusters of predicted phosphorylation sites partially disrupted PIN3 phosphorylation and caused defects in gravitropic bending in roots and hypocotyls. In particular, they impacted PIN3 polarity rearrangements in response to gravity and during feed-back regulation by auxin itself. Thus PIN phosphorylation, besides regulating transport activity and apical-basal targeting, is also important for the rapid polarity switches in response to environmental and endogenous signals.
- MeSH
- Arabidopsis účinky léků fyziologie MeSH
- fosforylace MeSH
- gravitropismus * MeSH
- kořeny rostlin účinky léků fyziologie MeSH
- kyseliny indoloctové farmakologie MeSH
- percepce tíhy MeSH
- polarita buněk * MeSH
- proteiny huseníčku genetika metabolismus MeSH
- regulátory růstu rostlin farmakologie MeSH
- sekvence aminokyselin MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Plants adjust their growth according to gravity. Gravitropism involves gravity perception, signal transduction, and asymmetric growth response, with organ bending as a consequence [1]. Asymmetric growth results from the asymmetric distribution of the plant-specific signaling molecule auxin [2] that is generated by lateral transport, mediated in the hypocotyl predominantly by the auxin transporter PIN-FORMED3 (PIN3) [3-5]. Gravity stimulation polarizes PIN3 to the bottom sides of endodermal cells, correlating with increased auxin accumulation in adjacent tissues at the lower side of the stimulated organ, where auxin induces cell elongation and, hence, organ bending. A curvature response allows the hypocotyl to resume straight growth at a defined angle [6], implying that at some point auxin symmetry is restored to prevent overbending. Here, we present initial insights into cellular and molecular mechanisms that lead to the termination of the tropic response. We identified an auxin feedback on PIN3 polarization as underlying mechanism that restores symmetry of the PIN3-dependent auxin flow. Thus, two mechanistically distinct PIN3 polarization events redirect auxin fluxes at different time points of the gravity response: first, gravity-mediated redirection of PIN3-mediated auxin flow toward the lower hypocotyl side, where auxin gradually accumulates and promotes growth, and later PIN3 polarization to the opposite cell side, depleting this auxin maximum to end the bending. Accordingly, genetic or pharmacological interference with the late PIN3 polarization prevents termination of the response and leads to hypocotyl overbending. This observation reveals a role of auxin feedback on PIN polarity in the termination of the tropic response.
- MeSH
- Arabidopsis genetika růst a vývoj fyziologie MeSH
- gravitropismus * MeSH
- kyseliny indoloctové metabolismus MeSH
- percepce tíhy * MeSH
- proteiny huseníčku genetika metabolismus MeSH
- regulátory růstu rostlin metabolismus MeSH
- výhonky rostlin růst a vývoj MeSH
- zpětná vazba fyziologická MeSH
- Publikační typ
- časopisecké články MeSH
Redirection of intercellular auxin fluxes via relocalization of the PIN-FORMED 3 (PIN3) and PIN7 auxin efflux carriers has been suggested to be necessary for the root gravitropic response. Cytokinins have also been proposed to play a role in controlling root gravitropism, but conclusive evidence is lacking. We present a detailed study of the dynamics of root bending early after gravistimulation, which revealed a delayed gravitropic response in transgenic lines with depleted endogenous cytokinins (Pro35S:AtCKX) and cytokinin signaling mutants. Pro35S:AtCKX lines, as well as a cytokinin receptor mutant ahk3, showed aberrations in the auxin response distribution in columella cells consistent with defects in the auxin transport machinery. Using in vivo real-time imaging of PIN3-GFP and PIN7-GFP in AtCKX3 overexpression and ahk3 backgrounds, we observed wild-type-like relocalization of PIN proteins in the columella early after gravistimulation, with gravity-induced relocalization of PIN7 faster than that of PIN3. Nonetheless, the cellular distribution of PIN3 and PIN7 and expression of PIN7 and the auxin influx carrier AUX1 was affected in AtCKX overexpression lines. Based on the retained cytokinin sensitivity in pin3 pin4 pin7 mutant, we propose the AUX1-mediated auxin transport rather than columella-located PIN proteins as a target of endogenous cytokinins in the control of root gravitropism.
- MeSH
- Arabidopsis účinky léků fyziologie MeSH
- biologické modely MeSH
- biologický transport účinky léků MeSH
- cytokininy farmakologie MeSH
- gravitace MeSH
- gravitropismus účinky léků MeSH
- kořeny rostlin účinky léků fyziologie MeSH
- kyseliny indoloctové metabolismus MeSH
- meristém účinky léků fyziologie MeSH
- proteiny huseníčku metabolismus MeSH
- signální transdukce účinky léků MeSH
- zelené fluorescenční proteiny metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
RAB GTPases are important directional regulators of intracellular vesicle transport. Membrane localization of RAB GTPases is mediated by C-terminal double geranylgeranylation. This post-translational modification is catalyzed by the alpha-beta-heterodimer catalytic core of RAB geranylgeranyl transferase (RAB-GGT), which cooperates with the RAB escort protein (REP) that presents a nascent RAB. Here, we show that RAB-geranylgeranylation activity is significantly reduced in two homozygous mutants of the major Arabidopsis beta-subunit of RAB-GGT (AtRGTB1), resulting in unprenylated RAB GTPases accumulation in the cytoplasm. Both endocytosis and exocytosis are downregulated in rgtb1 homozygotes defective in shoot growth and morphogenesis. Root gravitropism is normal in rgtb1 roots, but is significantly compromised in shoots. Mutants are defective in etiolation and show constitutive photomorphogenic phenotypes that cannot be rescued by brassinosteroid treatment, similarly to the det3 mutant that is also defective in the secretory pathway. Transcriptomic analysis revealed an upregulation of specific RAB GTPases in etiolated wild-type plants. Taken together, these data suggest that the downregulation of the secretory pathway is interpreted as a photomorphogenic signal in Arabidopsis.
- MeSH
- Arabidopsis genetika růst a vývoj metabolismus MeSH
- gravitropismus MeSH
- prenylace MeSH
- proteiny huseníčku genetika metabolismus MeSH
- rekombinantní fúzní proteiny genetika metabolismus MeSH
- transferasy genetika metabolismus MeSH
- výhonky rostlin genetika růst a vývoj MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Intercellular flow of the phytohormone auxin underpins multiple developmental processes in plants. Plant-specific pin-formed (PIN) proteins and several phosphoglycoprotein (PGP) transporters are crucial factors in auxin transport-related development, yet the molecular function of PINs remains unknown. Here, we show that PINs mediate auxin efflux from mammalian and yeast cells without needing additional plant-specific factors. Conditional gain-of-function alleles and quantitative measurements of auxin accumulation in Arabidopsis and tobacco cultured cells revealed that the action of PINs in auxin efflux is distinct from PGP, rate-limiting, specific to auxins, and sensitive to auxin transport inhibitors. This suggests a direct involvement of PINs in catalyzing cellular auxin efflux.
- MeSH
- ABC transportéry genetika metabolismus MeSH
- Arabidopsis cytologie fyziologie metabolismus růst a vývoj MeSH
- biologický transport MeSH
- buněčná membrána metabolismus MeSH
- financování organizované MeSH
- ftalimidy farmakologie MeSH
- gravitropismus MeSH
- HeLa buňky MeSH
- kinetika MeSH
- kořeny rostlin fyziologie MeSH
- kultivované buňky MeSH
- kyseliny indoloctové metabolismus MeSH
- kyseliny naftalenoctové metabolismus MeSH
- lidé MeSH
- membránové transportní proteiny genetika metabolismus MeSH
- mutace MeSH
- proteiny huseníčku genetika metabolismus MeSH
- Saccharomyces cerevisiae genetika MeSH
- tabák MeSH
- transfekce MeSH
- transformace genetická MeSH
- Check Tag
- lidé MeSH
strana 14-15 : ilustrace ; 25 cm
- MeSH
- česnek fyziologie MeSH
- fyziologie rostlin MeSH
- gravitropismus MeSH
- Pyrus fyziologie MeSH
- rostliny MeSH
- slivoň švestka fyziologie MeSH
- Publikační typ
- kazuistiky MeSH
