This review summarizes recent studies on lateral root formation that have begun to reveal detailed regulatory mechanisms at different developmental stages, with an emphasis on the multiple roles of ...auxin.
Abstract
Root systems can display variable architectures that contribute to survival strategies of plants. The model plant Arabidopsis thaliana possesses a tap root system, in which the primary root and lateral roots (LRs) are major architectural determinants. The phytohormone auxin fulfils multiple roles throughout LR development. In this review, we summarize recent advances in our understanding of four aspects of LR formation: (i) LR positioning, which determines the spatial distribution of lateral root primordia (LRP) and LRs along primary roots; (ii) LR initiation, encompassing the activation of nuclear migration in specified lateral root founder cells (LRFCs) up to the first asymmetric cell division; (iii) LR outgrowth, the 'primordium-intrinsic' patterning of de novo organ tissues and a meristem; and (iv) LR emergence, an interaction between LRP and overlaying tissues to allow passage through cell layers. We discuss how auxin signaling, embedded in a changing developmental context, plays important roles in all four phases. In addition, we discuss how rapid progress in gene network identification and analysis, modeling, and four-dimensional imaging techniques have led to an increasingly detailed understanding of the dynamic regulatory networks that control LR development.
Abstract
Plant development continues postembryonically with a lifelong ability to form new tissues and organs. Asymmetric cell division, coupled with fate segregation, is essential to create cellular ...diversity during tissue and organ formation. Arabidopsis (Arabidopsis thaliana) plants harboring mutations in the SCHIZORIZA (SCZ) gene display fate segregation defects in their roots, resulting in the presence of an additional layer of endodermis, production of root hairs from subepidermal tissue, and misexpression of several tissue identity markers. Some of these defects are observed in tissues where SCZ is not expressed, indicating that part of the SCZ function is nonautonomous. As a class B HEAT-SHOCK TRANSCRIPTION FACTOR (HSFB), the SCZ protein contains several conserved domains and motifs. However, which domain(s) discriminates SCZ from its family members to obtain a role in development remains unknown. Here, we investigate how each domain contributes to SCZ function in Arabidopsis root patterning by generating altered versions of SCZ by domain swapping and mutation. We show that the SCZ DNA-binding domain is the main factor for its developmental function, and that SCZ likely acts as a nonmotile transcriptional repressor. Our results demonstrate how members of the HSF family can evolve toward functions beyond stress response.
Domain–function analysis shows that evolution of the heat-shock transcription factor family gene SCHIZORIZA toward a function in development resides predominantly in its DNA-binding domain.
Lateral roots (LRs), which originate from the growing root, and adventitious roots (ARs), which are formed from non-root organs, are the main contributors to the post-embryonic root system in
...However, our knowledge of how formation of the root system is altered in response to diverse inductive cues is limited. Here, we show that
contributes to root system plasticity. When seedlings are grown vertically on medium,
is not expressed in LR founder cells. During AR initiation,
is expressed in AR founder cells and activates
also functions in LR formation and is activated in that context by
/
and not by
This indicates that divergent initial processes that lead to ARs and LRs may converge on a similar mechanism for primordium development. Furthermore, we demonstrated that when plants are grown in soil or upon wounding on medium, the primary root is able to produce both
-mediated and non-
-mediated roots. The discovery of
-mediated root-derived roots reveals a previously uncharacterized pathway that confers plasticity during the generation of root system architecture in response to different inductive cues.
The phytohormone auxin is a key factor in plant growth and development. Forward and reverse genetic strategies have identified important molecular components in auxin perception, signaling, and ...transport. These advances resulted in the identification of some of the underlying regulatory mechanisms as well as the emergence of functional frameworks for auxin action. This review focuses on the feedback loops that form an integrative part of these regulatory mechanisms.
Plants are sessile and have to cope with environmentally induced damage through modification of growth and defense pathways. How tissue regeneration is triggered in such responses and whether this ...involves stem cell activation is an open question. The stress hormone jasmonate (JA) plays well-established roles in wounding and defense responses. JA also affects growth, which is hitherto interpreted as a trade-off between growth and defense. Here, we describe a molecular network triggered by wound-induced JA that promotes stem cell activation and regeneration. JA regulates organizer cell activity in the root stem cell niche through the RBR-SCR network and stress response protein ERF115. Moreover, JA-induced ERF109 transcription stimulates CYCD6;1 expression, functions upstream of ERF115, and promotes regeneration. Soil penetration and response to nematode herbivory induce and require this JA-mediated regeneration response. Therefore, the JA tissue damage response pathway induces stem cell activation and regeneration and activates growth after environmental stress.
Display omitted
•The plant RETINOBLASTOMA homolog integrates wound signaling pathways•Jasmonate signaling promotes tissue regeneration•Synergy between jasmonate and auxin signaling in regulating regeneration•Jasmonate-mediated regeneration response is required for abiotic and biotic stresses
Stem cell activation and regeneration after tissue damage in Arabidopsis roots is mediated by a jasmonate signaling network.
Plants cope with the environment in a variety of ways, and ecological analyses attempt to capture this through life-history strategies or trait-based categorization. These approaches are limited ...because they treat the trade-off mechanisms that underlie plant responses as a black box. Approaches that involve the molecular or physiological analysis of plant responses to the environment have elucidated intricate connections between developmental and environmental signals, but in only a few well-studied model species. By considering diversity in the plant response to the environment as the adaptation of an information-processing network, new directions can be found for the study of life-history strategies, trade-offs and evolution in plants.
During plant growth, dividing cells in meristems must coordinate transitions from division to expansion and differentiation, thus generating three distinct developmental zones: the meristem, ...elongation zone and differentiation zone. Simultaneously, plants display tropisms, rapid adjustments of their direction of growth to adapt to environmental conditions. It is unclear how stable zonation is maintained during transient adjustments in growth direction. In Arabidopsis roots, many aspects of zonation are controlled by the phytohormone auxin and auxin-induced PLETHORA (PLT) transcription factors, both of which display a graded distribution with a maximum near the root tip. In addition, auxin is also pivotal for tropic responses. Here, using an iterative experimental and computational approach, we show how an interplay between auxin and PLTs controls zonation and gravitropism. We find that the PLT gradient is not a direct, proportionate readout of the auxin gradient. Rather, prolonged high auxin levels generate a narrow PLT transcription domain from which a gradient of PLT protein is subsequently generated through slow growth dilution and cell-to-cell movement. The resulting PLT levels define the location of developmental zones. In addition to slowly promoting PLT transcription, auxin also rapidly influences division, expansion and differentiation rates. We demonstrate how this specific regulatory design in which auxin cooperates with PLTs through different mechanisms and on different timescales enables both the fast tropic environmental responses and stable zonation dynamics necessary for coordinated cell differentiation.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Display omitted
•AIL/PLTs promote growth and division and oppose differentiation in roots and shoots.•Despite common functions, AIL/PLT target genes may differ in roots and shoots.•The root AIL/PLT ...target genes translate a persistent auxin maximum into patterned cell division and cell differentiation zones.
Growth at the root tip and organ generation at the shoot tip depend on the proper functioning of apical meristems and the transitioning of meristematic cell descendants from a proliferating state to cell elongation and differentiation. Members of the AINTEGUMENTA-LIKE/PLETHORA (AIL/PLT) transcription factor family, a clade of two-AP2 domain proteins, specify both stem cell fate and control cellular progression of stem cell daughter cells toward differentiation. Here we highlight the importance of an AIL/PLT protein gradient in controlling distinct cellular behaviors in the root through the regulation of distinct targets in different parts of the root tip. Within the shoot, AIL/PLT proteins also promote organ growth and inhibit differentiation pointing to conserved roles in meristem function. However, they exhibit unequal genetic redundancy in these functions and do not always act in a purely additive manner. Differences in AIL/PLT regulation and perhaps transcriptional targets in roots and shoots suggest that these growth regulators have adapted to mediate growth control in distinct ways in these organ systems.
Vesicle trafficking is essential for the generation of asymmetries, which are central to multicellular development. Core components of the vesicle transport machinery, such as ADP-ribosylation factor ...(ARF) GTPases, have been studied primarily at the single-cell level. Here, we analyze developmental functions of the ARF1 subclass of the Arabidopsis thaliana multigene ARF family. Six virtually identical ARF1 genes are ubiquitously expressed, and single loss-of-function mutants in these genes reveal no obvious developmental phenotypes. Fluorescence colocalization studies reveal that ARF1 is localized to the Golgi apparatus and endocytic organelles in both onion (Allium cepa) and Arabidopsis cells. Apical-basal polarity of epidermal cells, reflected by the position of root hair outgrowth, is affected when ARF1 mutants are expressed at early stages of cell differentiation but after they exit mitosis. Genetic interactions during root hair tip growth and localization suggest that the ROP2 protein is a target of ARF1 action, but its localization is slowly affected upon ARF1 manipulation when compared with that of Golgi and endocytic markers. Localization of a second potential target of ARF1 action, PIN2, is also affected with slow kinetics. Although extreme redundancy precludes conventional genetic dissection of ARF1 functions, our approach separates different ARF1 downstream networks involved in local and specific aspects of cell polarity.
Nutrient computation for root architecture Bisseling, Ton; Scheres, Ben
Science (American Association for the Advancement of Science),
10/2014, Letnik:
346, Številka:
6207
Journal Article
Recenzirano
Plants sense and respond to nutrients using a peptide signaling system
Nitrogen is a major limiting nutrient for plants. Root systems acquire nitrogen through uptake of nutrients such as nitrate from ...the soil. Some plants can also obtain nitrogen by establishing a root nodule symbiosis with N-fixing bacteria. Whatever the means to acquire nutrients, an investment of the plant is required in which root architecture is suitably adapted. Therefore, plants integrate local and global nutrient cues to spend resources efficiently. On page 343 in this issue, Tabata
et al.
(
1
) identify a peptide signaling mechanism by which the root locally senses N limitation in the soil, and communicates with the shoot, which then signals back to the root to stimulate lateral root growth in regions with a high nitrate content to facilitate nitrate uptake.
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