Stem cells must balance self-renewal and differentiation; thus, their activities are precisely controlled. In plants, the control circuits that underlie division and differentiation within meristems ...have been well studied, but those that underlie feedback on meristems from lateral organs remain largely unknown. Here we show that long-distance auxin transport mediates this feedback in a non-cell-autonomous manner. A low-auxin zone is associated with the shoot apical meristem (SAM) organization center, and auxin levels negatively affect SAM size. Using computational model simulations, we show that auxin transport from lateral organs can inhibit auxin transport from the SAM through an auxin transport switch and thus maintain SAM auxin homeostasis and SAM size. Genetic and microsurgical analyses confirmed the model's predictions. In addition, the model explains temporary change in SAM size of yabby mutants. Our study suggests that the canalization-based auxin flux can be widely adapted as a feedback control mechanism in plants.
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•A low-level auxin region exists in the plant shoot apical meristem (SAM)•Auxin level is negatively correlated to the SAM size•Auxin transport from lateral organs inhibits that from the SAM, maintaining SAM size•Auxin transport from branches further triggers changes in SAM size in yab mutants
Combining computational simulation and experimental observation of competitive long-distance auxin flows from the plant shoot apical meristem (SAM) and lateral organs, Shi et al. report that lateral organs feed back to SAM stem cells through an auxin transport switch complementary to the local WUS-CLV feedback loop to maintain meristem size.
-1-naphthylphthalamic acid (NPA) is a key inhibitor of directional (polar) transport of the hormone auxin in plants. For decades, it has been a pivotal tool in elucidating the unique polar auxin ...transport-based processes underlying plant growth and development. Its exact mode of action has long been sought after and is still being debated, with prevailing mechanistic schemes describing only indirect connections between NPA and the main transporters responsible for directional transport, namely PIN auxin exporters. Here we present data supporting a model in which NPA associates with PINs in a more direct manner than hitherto postulated. We show that NPA inhibits PIN activity in a heterologous oocyte system and that expression of NPA-sensitive PINs in plant, yeast, and oocyte membranes leads to specific saturable NPA binding. We thus propose that PINs are a bona fide NPA target. This offers a straightforward molecular basis for NPA inhibition of PIN-dependent auxin transport and a logical parsimonious explanation for the known physiological effects of NPA on plant growth, as well as an alternative hypothesis to interpret past and future results. We also introduce PIN dimerization and describe an effect of NPA on this, suggesting that NPA binding could be exploited to gain insights into structural aspects of PINs related to their transport mechanism.
An Update on the Signals Controlling Shoot Branching Barbier, Francois F.; Dun, Elizabeth A.; Kerr, Stephanie C. ...
Trends in plant science,
March 2019, 2019-03-00, 20190301, Letnik:
24, Številka:
3
Journal Article
Recenzirano
Many new questions on the regulation of shoot branching have been raised in recent years, prompting a review and reassessment of the role of each signal involved. Sugars and their signaling networks ...have been attributed a major role in the early events of axillary bud outgrowth, whereas cytokinin appears to play a critical role in the modulation of this process in response to the environment. Perception of the recently discovered hormone strigolactone is now quite well understood, while the downstream targets remain largely unknown. Recent literature has highlighted that auxin export from a bud is important for its subsequent growth.
Sugars play a major role during the very early events of bud outgrowth, likely through interactions with hormone pathways.
Cytokinins play a major role in shoot branching, but are not absolutely required for bud outgrowth in response to decapitation.
Auxin depletion in the stem and auxin export from the bud are important for sustained bud growth rather than initial bud release.
The strigolactone signaling proteins have been identified but their transcriptional and other targets are still not well understood.
BRC1 is an integrator of multiple bud outgrowth regulatory pathways to determine the activation potential of buds, but BRC1-independent pathways are also involved.
Cell polarity is a key feature in the development of multicellular organisms. For instance, asymmetrically localized plasma-membrane-integral PIN-FORMED (PIN) proteins direct transcellular fluxes of ...the phytohormone auxin that govern plant development. Fine-tuned auxin flux is important for root protophloem sieve element differentiation and requires the interacting plasma-membrane-associated BREVIS RADIX (BRX) and PROTEIN KINASE ASSOCIATED WITH BRX (PAX) proteins. We observed “donut-like” polar PIN localization in developing sieve elements that depends on complementary, “muffin-like” polar localization of BRX and PAX. Plasma membrane association and polarity of PAX, and indirectly BRX, largely depends on phosphatidylinositol-4,5-bisphosphate. Consistently, mutants in phosphatidylinositol-4-phosphate 5-kinases (PIP5Ks) display protophloem differentiation defects similar to brx mutants. The same PIP5Ks are in complex with BRX and display “muffin-like” polar localization. Our data suggest that the BRX-PAX module recruits PIP5Ks to reinforce PAX polarity and thereby the polarity of all three proteins, which is required to maintain a local PIN minimum.
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•Unique PIN localization in root protophloem depends on the PIN regulators BRX and PAX•Phosphatidylinositol-4,5-bisphosphate promotes the polarity of PAX and indirectly BRX•Together, BRX and PAX recruit PIP5Ks to reinforce the polarity of all three proteins•This self-reinforcing polarity module is required to maintain a local PIN minimum
Cell polarity is an intriguing feature of animal and plant development, yet examples of molecular mechanisms that maintain context-specific polarity remain scarce. In their study, Marhava et al. present a self-reinforcing polarity module in plant development, which is necessary for proper differentiation of protophloem, an essential tissue of plant meristems.
Auxin-dependent cell expansion is crucial for initiation of fiber cells in cotton (Gossypium hirsutum), which ultimately determines fiber yield and quality. However, the regulation of this process is ...far from being well understood. In this study, we demonstrate an antagonistic effect between cytokinin (CK) and auxin on cotton fiber initiation. In vitro and in planta experiments indicate that enhanced CK levels can reduce auxin accumulation in the ovule integument, which may account for the defects in the fiberless mutant xu142fl. In turn, supplementation with auxin can recover fiber growth of CK-treated ovules and mutant ovules. We further found that GhPIN3a is a key auxin transporter for fiber-cell initiation and is polarly localized to the plasma membranes of non-fiber cells, but not to those of fiber cells. This polar localization allows auxin to be transported within the ovule integument while specifically accumulating in fiber cells. We show that CKs antagonize the promotive effect of auxin on fiber cell initiation by undermining asymmetric accumulation of auxin in the ovule epidermis through down-regulation of GhPIN3a and disturbance of the polar localization of the protein.
Auxin is a major phytohormone that controls numerous aspects of plant development and coordinates plant responses to the environment. Morphogenic gradients of auxin govern cell fate decisions and ...underlie plant phenotypic plasticity. Polar auxin transport plays a central role in auxin maxima generation. The discovery of the exquisite spatiotemporal expression patterns of auxin biosynthesis genes of the WEI8/TAR and YUC families suggested that local auxin production may contribute to the formation of auxin maxima. Herein, we systematically addressed the role of local auxin biosynthesis in plant development and responses to the stress phytohormone ethylene by manipulating spatiotemporal patterns of WEI8. Our study revealed that local auxin biosynthesis and transport act synergistically and are individually dispensable for root meristem maintenance. In contrast, flower fertility and root responses to ethylene require local auxin production that cannot be fully compensated for by transport in the generation of morphogenic auxin maxima.
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•Local auxin production in roots is required for maintaining functional root meristems•Local biosynthesis and transport of auxin cooperate at generating robust auxin maxima•Auxin produced in the root quiescent center is sufficient for root meristem viability
The plant hormone auxin is a key regulator of plant growth and development. Brumos et al. show that local biosynthesis and polar transport of auxin act in concert to produce robust auxin maxima in the root quiescent center to sustain the meristematic potential of the root stem cell niche.
Melatonin (
-acetyl-5-methoxytryptamine) plays important roles in regulating both biotic and abiotic stress tolerance, biological rhythms, plant growth and development. Sharing the same substrate ...(tryptophan) for the biosynthesis, melatonin and auxin also have similar effects in plant development. However, the specific function of melatonin in modulating plant root growth and the relationship between melatonin and auxin as well as underlying mechanisms are still unclear. In this study, we found high concentration of melatonin remarkably inhibited root growth in
by reducing root meristem size. Further studies showed that melatonin negatively regulated auxin biosynthesis, the expression of PINFORMED (PIN) proteins as well as auxin response in
. Moreover, the root growth of the triple mutant
was more tolerant than that of wild-type in response to melatonin treatment, suggesting the essential role of PIN1/3/7 in melatonin-mediated root growth. Combination treatment of melatonin and 5-Triiodobenzoic acid (TIBA) did not enhance melatonin-mediated reduction of root meristem size, indicating that polar auxin transport (PAT) may be necessary for the regulation of root meristem size by melatonin treatment. Taken together, this study indicates that melatonin regulates root growth in
, through auxin synthesis and polar auxin transport, at least partially.
Summary
Tropisms, growth responses to environmental stimuli such as light or gravity, are spectacular examples of adaptive plant development. The plant hormone auxin serves as a major coordinative ...signal. The PIN auxin exporters, through their dynamic polar subcellular localizations, redirect auxin fluxes in response to environmental stimuli and the resulting auxin gradients across organs underlie differential cell elongation and bending. In this review, we discuss recent advances concerning regulations of PIN polarity during tropisms, focusing on PIN phosphorylation and trafficking. We also cover how environmental cues regulate PIN actions during tropisms, as well as the crucial role of auxin feedback on PIN polarity during bending termination. Finally, the interactions between different tropisms are reviewed to understand plant adaptive growth in the natural environment.
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