A Retro-Perspective on Auxin Transport

Geisler, Markus

doi:10.3389/fpls.2021.756968

Cited by 22 publications

(18 citation statements)

References 160 publications

(256 reference statements)

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“…Auxin and cytokinin play key roles in vascular system development and in part, exert their effects on plant growth via vascular transport [37][38][39][40][41][42][43]. However, the antagonistic actions of auxin and cytokinin on the shoot/root growth ratio are operational in the earliest land plants, the non-vascular bryophytes, which suggests that it predates the emergence of the vascular system.…”

Section: Auxin-and Cytokinin-dependent Control Of the Growth Ratio Of...mentioning

confidence: 99%

Auxin/Cytokinin Antagonistic Control of the Shoot/Root Growth Ratio and Its Relevance for Adaptation to Drought and Nutrient Deficiency Stresses

Kurepa

Smalle

2022

IJMS

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The hormones auxin and cytokinin regulate numerous aspects of plant development and often act as an antagonistic hormone pair. One of the more striking examples of the auxin/cytokinin antagonism involves regulation of the shoot/root growth ratio in which cytokinin promotes shoot and inhibits root growth, whereas auxin does the opposite. Control of the shoot/root growth ratio is essential for the survival of terrestrial plants because it allows growth adaptations to water and mineral nutrient availability in the soil. Because a decrease in shoot growth combined with an increase in root growth leads to survival under drought stress and nutrient limiting conditions, it was not surprising to find that auxin promotes, while cytokinin reduces, drought stress tolerance and nutrient uptake. Recent data show that drought stress and nutrient availability also alter the cytokinin and auxin signaling and biosynthesis pathways and that this stress-induced regulation affects cytokinin and auxin in the opposite manner. These antagonistic effects of cytokinin and auxin suggested that each hormone directly and negatively regulates biosynthesis or signaling of the other. However, a growing body of evidence supports unidirectional regulation, with auxin emerging as the primary regulatory component. This master regulatory role of auxin may not come as a surprise when viewed from an evolutionary perspective.

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Section: Auxin-and Cytokinin-dependent Control Of the Growth Ratio Of...mentioning

confidence: 99%

Auxin/Cytokinin Antagonistic Control of the Shoot/Root Growth Ratio and Its Relevance for Adaptation to Drought and Nutrient Deficiency Stresses

Kurepa

Smalle

2022

IJMS

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“…The importance of orchestrated shootward auxin distribution along the root epidermis between the meristem and differentiation zone for the efficient modulation of root growth has been demonstrated repeatedly [ 3 , 4 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 ]. In 1990, Okada and Shimura [ 29 ] identified six Arabidopsis thaliana mutants with an apparent wavy phenotype, including the loss of function of a plasma membrane-located auxin influx carrier, AUXIN RESISTANT 1 (AUX1) [ 16 , 25 , 28 , 29 , 30 , 31 , 32 , 33 , 34 ]. The adaptation of root growth patterns is often studied by observing seedlings growing on an agar-enriched medium [ 35 , 36 ].…”

Section: Introductionmentioning

confidence: 99%

Throttling Growth Speed: Evaluation of aux1-7 Root Growth Profile by Combining D-Root system and Root Penetration Assay

García-González

Lacek

Weckwerth

et al. 2022

Plants

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Directional root growth control is crucial for plant fitness. The degree of root growth deviation depends on several factors, whereby exogenous growth conditions have a profound impact. The perception of mechanical impedance by wild-type roots results in the modulation of root growth traits, and it is known that gravitropic stimulus influences distinct root movement patterns in concert with mechanoadaptation. Mutants with reduced shootward auxin transport are described as being numb towards mechanostimulus and gravistimulus, whereby different growth conditions on agar-supplemented medium have a profound effect on how much directional root growth and root movement patterns differ between wild types and mutants. To reduce the impact of unilateral mechanostimulus on roots grown along agar-supplemented medium, we compared the root movement of Col-0 and auxin resistant 1-7 in a root penetration assay to test how both lines adjust the growth patterns of evenly mechanostimulated roots. We combined the assay with the D-root system to reduce light-induced growth deviation. Moreover, the impact of sucrose supplementation in the growth medium was investigated because exogenous sugar enhances root growth deviation in the vertical direction. Overall, we observed a more regular growth pattern for Col-0 but evaluated a higher level of skewing of aux1-7 compared to the wild type than known from published data. Finally, the tracking of the growth rate of the gravistimulated roots revealed that Col-0 has a throttling elongation rate during the bending process, but aux1-7 does not.

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“…Beside the predominant active auxin, IAA (indole-3-acetic acid), indole-3-butyric acid (IBA) has recently gained more and more interest, also because it is the active ingredient in plant propagation media (Frick and Strader, 2018). A special feature of auxins is their cell-to-cell transport, designated as polar auxin transport (PAT), which is provided by the combined action of plasma membraneembedded auxin transporters (reviewed in Friml, 2021;Geisler, 2021;Hammes et al, 2022). An interesting finding thus was that IAA and IBA employ different transporter subsets: while IAA is predominantly transported by members of the AUX1/LAX (AUX1 (Auxin-resistant1) and like AUX1), PIN (Pin-formed) and ABCB (B-type ABC (ATPbinding cassette transporter) families ;Geisler, 2021;Hammes et al, 2022), examined members of these families apparently do not transport IBA (reviewed in Damodaran and Strader, 2019;Frick and Strader, 2018).…”

Section: Introductionmentioning

confidence: 99%

“…While most of the molecular mechanisms and players underlying growth–defense tradeoffs are unknown, it has become obvious that they are coordinately controlled by several classes of plant hormones as well as by hormone crosstalk (Huot et al, 2014; Lozano-Duran and Zipfel, 2015). Plant hormones were initially identified as growth regulators, with auxins being the first identified and probably the best-studied (Friml, 2021; Geisler, 2021). Beside the predominant active auxin, IAA (indole-3-acetic acid), indole-3-butyric acid (IBA) has recently gained more and more interest, also because it is the active ingredient in plant propagation media (Frick and Strader, 2018).…”

Section: Introductionmentioning

confidence: 99%

“…A special feature of auxins is their cell-to-cell transport, designated as polar auxin transport (PAT), which is provided by the combined action of plasma membrane-embedded auxin transporters (reviewed in Friml, 2021; Geisler, 2021; Hammes et al, 2022). An interesting finding thus was that IAA and IBA employ different transporter subsets: while IAA is predominantly transported by members of the AUX1/LAX (AUX1 (Auxin-resistant1) and like AUX1), PIN (Pin-formed) and ABCB (B-type ABC (ATP-binding cassette transporter) families; Geisler, 2021; Hammes et al, 2022), examined members of these families apparently do not transport IBA (reviewed in Damodaran and Strader, 2019; Frick and Strader, 2018). On the other hand, IBA was shown to be exported over the PM by different members of the G family of ABC transporters (ABCGs) that seem not to transport IAA (Ruzicka et al, 2010; Strader and Bartel, 2011).…”

Section: Introductionmentioning

confidence: 99%

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A phospho-switch provided by LRR receptor-like kinase, ALK1/QSK1/KIN7, prioritizes ABCG36/PEN3/PDR8 transport toward defense

Aryal

Xia

et al. 2022

Preprint

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Based on its proposed substrate preferences, the ABC transporter, ABCG36/PDR8/PEN3, from the model plant Arabidopsis stands at the cross-road between growth and defence. Recently, ABCG36 was shown to export a few indolic compounds, including the auxin precursor, indole-3-butyric acid (IBA), and to be implicated in the export of the major phytoalexin of Arabidopsis, camalexin, although clear-cut proof of camalexin transport activity is still lacking.Here we provide strong evidence that ABCG36 catalyses the direct, ATP-dependent export of camalexin over the plasma membrane, however, most likely in functional interplay with non-camalexin transporting ABCG isoforms. We identify the leucin-rich repeat receptor-like kinase, Auxin-induced LRR Kinase1 (ALK1/KIN7/QSK1), as a functional kinase to physically interact with and phosphorylate ABCG36. ABCG36 phosphorylation by ALK1 represses unilaterally IBA but not camalexin export leading to a prioritization of ABCG transport toward defense. As a consequence, phospho-dead mutants of ABCG36, like alk1 and abcg36 alleles, are hypersensitive toward infection with the root pathogen, F. oxysporum, caused by elevated fungal progression.Our findings indicate a novel, direct regulatory circuit between a receptor kinase and an ABC transporter determining transporter substrate specificity. It appears that growth and defense balance decisions in plants are performed on the transporter level by means of a reversible phospho-switch.

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A Retro-Perspective on Auxin Transport

Cited by 22 publications

References 160 publications

Auxin/Cytokinin Antagonistic Control of the Shoot/Root Growth Ratio and Its Relevance for Adaptation to Drought and Nutrient Deficiency Stresses

Auxin/Cytokinin Antagonistic Control of the Shoot/Root Growth Ratio and Its Relevance for Adaptation to Drought and Nutrient Deficiency Stresses

Throttling Growth Speed: Evaluation of aux1-7 Root Growth Profile by Combining D-Root system and Root Penetration Assay

A phospho-switch provided by LRR receptor-like kinase, ALK1/QSK1/KIN7, prioritizes ABCG36/PEN3/PDR8 transport toward defense

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