Plants exhibit a unique developmental flexibility to ever-changing environmental conditions. To achieve their profound adaptability, plants are able to maintain permanent stem cell populations and ...form new organs during the entire plant life cycle. Signaling substances, called plant hormones, such as auxin, cytokinin, abscisic acid, brassinosteroid, ethylene, gibberellin, jasmonic acid, and strigolactone, govern and coordinate these developmental processes. Physiological and genetic studies have dissected the molecular components of signal perception and transduction of the individual hormonal pathways. However, over recent years it has become evident that hormones do not act only in a linear pathway. Hormonal pathways are interconnected by a complex network of interactions and feedback circuits that determines the final outcome of the individual hormone actions. This raises questions about the molecular mechanisms underlying hormonal cross talk and about how these hormonal networks are established, maintained, and modulated throughout plant development.
Plants are continuously exposed to a myriad of external signals such as uctuating nutrients availability, drought, heat, cold, high salinity, or pathogen/pest attacks that can severely affect their ...development, growth, and fertility. As sessile organisms, plants must therefore be able to sense and rapidly react to these external inputs, activate efcient responses, and adjust development to changing conditions. In recent years, signicant progress has been made towards understanding the molecular mechanisms underlying the intricate and complex communication between plants and the environment. It is now becoming increasingly evident that hormones have an important regulatory role in plant adaptation and defense mechanisms.
▶ Mechanisms controlling the spatiotemporal positioning of lateral roots. ▶ Auxin regulates lateral root organogenesis through successively acting auxin response modules. ▶ Small RNA regulates ...lateral root organogenesis through fine tuning auxin signaling pathway. ▶
ACR4 receptor-like kinase non-cell and cell autonomously controls lateral root organogenesis.
Unlike locomotive organisms capable of actively approaching essential resources, sessile plants must efficiently exploit their habitat for water and nutrients. This involves root-mediated underground interactions allowing plants to adapt to soils of diverse qualities. The root system of plants is a dynamic structure that modulates primary root growth and root branching by continuous integration of environmental inputs, such as nutrition availability, soil aeration, humidity, or salinity. Root branching is an extremely flexible means to rapidly adjust the overall surface of the root system and plants have evolved efficient control mechanisms, including, firstly initiation, when and where to start lateral root formation; secondly lateral root primordia organogenesis, during which the development of primordia can be arrested for a certain time; and thirdly lateral root emergence. Our review will focus on the most recent advances in understanding the molecular mechanisms involved in the regulation of lateral root initiation and organogenesis with the main focus on root system of the model plant
Arabidopsis thaliana.
Hormones, such as auxin and cytokinin, are involved in the complex molecular network that regulates the coordinated development of plant organs. Genes controlling ovule patterning have been ...identified and studied in detail; however, the roles of auxin and cytokinin in ovule development are largely unknown. Here we show that key cytokinin pathway genes, such as isopentenyltransferase and cytokinin receptors, are expressed during ovule development. Also, in a cre1-12 ahk2-2 ahk3-3 triple mutant with severely reduced cytokinin perception, expression of the auxin efflux facilitator PIN-FORMED 1 (PIN1) was severely reduced. In sporocyteless/nozzle (spl/nzz) mutants, which show a similar phenotype to the cre1-12 ahk2-2 ahk3-3 triple mutant, PIN1 expression is also reduced. Treatment with the exogenous cytokinin N 6 -benzylaminopurine also altered both auxin distribution and patterning of the ovule; this process required the homeodomain transcription factor BELL1 (BEL1). Thus, this article shows that cytokinin regulates ovule development through the regulation of PIN1. Furthermore, the transcription factors BEL1 and SPL/NZZ, previously described as key regulators of ovule development, are needed for the auxin and cytokinin signaling pathways for the correct patterning of the ovule.
Plants develop new organs to adjust their bodies to dynamic changes in the environment. How independent organs achieve anisotropic shapes and polarities is poorly understood. To address this ...question, we constructed a mechano-biochemical model for
root meristem growth that integrates biologically plausible principles. Computer model simulations demonstrate how differential growth of neighboring tissues results in the initial symmetry-breaking leading to anisotropic root growth. Furthermore, the root growth feeds back on a polar transport network of the growth regulator auxin. Model, predictions are in close agreement with in vivo patterns of anisotropic growth, auxin distribution, and cell polarity, as well as several root phenotypes caused by chemical, mechanical, or genetic perturbations. Our study demonstrates that the combination of tissue mechanics and polar auxin transport organizes anisotropic root growth and cell polarities during organ outgrowth. Therefore, a mobile auxin signal transported through immobile cells drives polarity and growth mechanics to coordinate complex organ development.
Nitrate is both a nitrogen source for higher plants and a signal molecule regulating their development. In
Arabidopsis, the NRT1.1 nitrate transporter is crucial for nitrate signaling governing root ...growth, and has been proposed to act as a nitrate sensor. However, the sensing mechanism is unknown. Herein we show that NRT1.1 not only transports nitrate but also facilitates uptake of the phytohormone auxin. Moreover, nitrate inhibits NRT1.1-dependent auxin uptake, suggesting that transduction of nitrate signal by NRT1.1 is associated with a modification of auxin transport. Among other effects, auxin stimulates lateral root development. Mutation of
NRT1.1 enhances both auxin accumulation in lateral roots and growth of these roots at low, but not high, nitrate concentration. Thus, we propose that NRT1.1 represses lateral root growth at low nitrate availability by promoting basipetal auxin transport out of these roots. This defines a mechanism connecting nutrient and hormone signaling during organ development.
► The NRT1.1 nitrate (NO
3
−
) transporter/sensor acts as an auxin influx facilitator ► NO
3
−
sensing by NRT1.1 involves inhibition of its auxin transport activity by NO
3
−
► NRT1.1 modulates auxin gradients in lateral root primordia in response to NO
3
−
► NRT1.1 represses lateral root growth at low external NO
3
−
concentration
Wound healing in plant tissues, consisting of rigid cell wall-encapsulated cells, represents a considerable challenge and occurs through largely unknown mechanisms distinct from those in animals. ...Owing to their inability to migrate, plant cells rely on targeted cell division and expansion to regenerate wounds. Strict coordination of these wound-induced responses is essential to ensure efficient, spatially restricted wound healing. Single-cell tracking by live imaging allowed us to gain mechanistic insight into the wound perception and coordination of wound responses after laser-based wounding in Arabidopsis root. We revealed a crucial contribution of the collapse of damaged cells in wound perception and detected an auxin increase specific to cells immediately adjacent to the wound. This localized auxin increase balances wound-induced cell expansion and restorative division rates in a dose-dependent manner, leading to tumorous overproliferation when the canonical TIR1 auxin signaling is disrupted. Auxin and wound-induced turgor pressure changes together also spatially define the activation of key components of regeneration, such as the transcription regulator ERF115. Our observations suggest that the wound signaling involves the sensing of collapse of damaged cells and a local auxin signaling activation to coordinate the downstream transcriptional responses in the immediate wound vicinity.
Synchronized tissue polarization during regeneration or de novo vascular tissue formation is a plant-specific example of intercellular communication and coordinated development. According to the ...canalization hypothesis, the plant hormone auxin serves as polarizing signal that mediates directional channel formation underlying the spatio-temporal vasculature patterning. A necessary part of canalization is a positive feedback between auxin signaling and polarity of the intercellular auxin flow. The cellular and molecular mechanisms of this process are still poorly understood, not the least, because of a lack of a suitable model system. We show that the main genetic model plant, Arabidopsis (Arabidopsis thaliana) can be used to study the canalization during vascular cambium regeneration and new vasculature formation. We monitored localized auxin responses, directional auxin-transport channels formation, and establishment of new vascular cambium polarity during regenerative processes after stem wounding. The increased auxin response above and around the wound preceded the formation of PIN1 auxin transporter-marked channels from the primarily homogenous tissue and the transient, gradual changes in PIN1 localization preceded the polarity of newly formed vascular tissue. Thus, Arabidopsis is a useful model for studies of coordinated tissue polarization and vasculature formation after wounding allowing for genetic and mechanistic dissection of the canalization hypothesis.
Plants exhibit an amazing developmental flexibility. Plant embryogenesis results in the establishment of a simple apical-basal axis represented by apical shoot and basal root meristems. Later, during ...postembryonic growth, shaping of the plant body continues by the formation and activation of numerous adjacent meristems that give rise to lateral shoot branches, leaves, flowers, or lateral roots. This developmental plasticity reflects an important feature of the plant's life strategy based on the rapid reaction to different environmental stimuli, such as temperature fluctuations, availability of nutrients, light or water and response resulting in modulation of developmental programs. Plant hormones are important endogenous factors for the integration of these environmental inputs and regulation of plant development. After a period of studies focused primarily on single hormonal pathways that enabled us to understand the hormone perception and signal transduction mechanisms, it became obvious that the developmental output mediated by a single hormonal pathway is largely modified through a whole network of interactions with other hormonal pathways. In this review, we will summarize recent knowledge on hormonal networks that regulate the development and growth of root with focus on the hormonal interactions that shape the root apical meristem.
Lateral root formation is a major determinant of root systems architecture. The degree of root branching impacts the efficiency of water uptake, acquisition of nutrients and anchorage by plants. ...Understanding the regulation of lateral root development is therefore of vital agronomic importance. The molecular and cellular basis of lateral root formation has been most extensively studied in the plant model
Arabidopsis thaliana (Arabidopsis). Significant progress has recently been made in identifying many new
Arabidopsis genes that regulate lateral root initiation, patterning and emergence processes. We review how these studies have revealed that the plant hormone auxin represents a common signal that integrates these distinct yet interconnected developmental processes.
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