Two recent studies highlight the role of stem cell activation as a response to tissue damage and wounding.
Two recent studies highlight the role of stem cell activation as a response to tissue damage ...and wounding.
Apical growth in plants initiates upon seed germination, whereas radial growth is primed only during early ontogenesis in procambium cells and activated later by the vascular cambium
. Although it is ...not known how radial growth is organized and regulated in plants, this system resembles the developmental competence observed in some animal systems, in which pre-existing patterns of developmental potential are established early on
. Here we show that in Arabidopsis the initiation of radial growth occurs around early protophloem-sieve-element cell files of the root procambial tissue. In this domain, cytokinin signalling promotes the expression of a pair of mobile transcription factors-PHLOEM EARLY DOF 1 (PEAR1) and PHLOEM EARLY DOF 2 (PEAR2)-and their four homologues (DOF6, TMO6, OBP2 and HCA2), which we collectively name PEAR proteins. The PEAR proteins form a short-range concentration gradient that peaks at protophloem sieve elements, and activates gene expression that promotes radial growth. The expression and function of PEAR proteins are antagonized by the HD-ZIP III proteins, well-known polarity transcription factors
-the expression of which is concentrated in the more-internal domain of radially non-dividing procambial cells by the function of auxin, and mobile miR165 and miR166 microRNAs. The PEAR proteins locally promote transcription of their inhibitory HD-ZIP III genes, and thereby establish a negative-feedback loop that forms a robust boundary that demarks the zone of cell division. Taken together, our data establish that during root procambial development there exists a network in which a module that links PEAR and HD-ZIP III transcription factors integrates spatial information of the hormonal domains and miRNA gradients to provide adjacent zones of dividing and more-quiescent cells, which forms a foundation for further radial growth.
Higher plant vasculature is characterized by two distinct developmental phases. Initially, a well-defined radial primary pattern is established. In eudicots, this is followed by secondary growth, ...which involves development of the cambium and is required for efficient water and nutrient transport and wood formation. Regulation of secondary growth involves several phytohormones, and cytokinins have been implicated as key players, particularly in the activation of cell proliferation, but the molecular mechanisms mediating this hormonal control remain unknown. Here we show that the genes encoding the transcription factor AINTEGUMENTA (ANT) and the D-type cyclin CYCD3;1 are expressed in the vascular cambium of Arabidopsis roots, respond to cytokinins and are both required for proper root secondary thickening. Cytokinin regulation of ANT and CYCD3 also occurs during secondary thickening of poplar stems, suggesting this represents a conserved regulatory mechanism.
Coordinating growth and patterning is essential for eukaryote morphogenesis. In plants, auxin is a key regulator of morphogenesis implicated throughout development. Despite this central role, our ...understanding of how auxin coordinates cell fate and growth changes is still limited. Here, we addressed this question using a combination of genomic screens to delve into the transcriptional network induced by auxin at the earliest stage of flower development, prior to morphological changes. We identify a shoot-specific network suggesting that auxin initiates growth through an antagonistic regulation of growth-promoting and growth-repressive hormones, quasi-synchronously to floral fate specification. We further identify two DNA-binding One Zinc Finger (DOF) transcription factors acting in an auxin-dependent network that could interface growth and cell fate from the early stages of flower development onward.
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•Pharmacological approach to probe transcriptional responses in shoot meristems•Analysis of a shoot-specific network regulated by auxin during flower initiation•Two DOF transcription factors are induced in flower primordia•The DOF genes potentially link growth to organ identity acquisition
Plant biology; Plant development; Omics; Transcriptomics
The stems and roots of most dicot plants increase in diameter by radial growth, due to the activity of secondary meristems. Two types of meristems function in secondary plant body formation: the ...vascular cambium, which gives rise to secondary xylem and phloem, and the cork cambium, which produces a bark layer that replaces the epidermis and protects the plant stem from mechanical damage and pathogens. Cambial development, the initiation and activity of the vascular cambium, leads to an accumulation of wood, the secondary xylem tissue. The thick, cellulose‐rich cell walls of wood provide a source of cellulose and have the potential to be used as a raw material for sustainable and renewable energy production. In this review, we will discuss what is known about the mechanisms regulating the cambium and secondary tissue development.
The developmental ontogeny of the vascular system (consisting of xylem, phloem and procambium) is poorly understood despite its central role in plant physiology. We show that in the Arabidopsis root ...meristem, xylem cell lineages are specified early, whereas phloem and procambium are established through a set of asymmetric cell divisions. These divisions require the WOODEN LEG (WOL) gene. The WOL gene encodes a novel two-component signal transducer with an unusual tandem arrangement of two receiver domains. It is expressed specifically in the vasculature from the early stages of embryogenesis on, consistent with a role as a sensor for vascular morphogenesis.
Cytokinin phytohormones regulate a variety of developmental processes in the root such as meristem size, vascular pattern, and root architecture 1–3. Long-distance transport of cytokinin is supported ...by the discovery of cytokinins in xylem and phloem sap 4 and by grafting experiments between wild-type and cytokinin biosynthesis mutants 5. Acropetal transport of cytokinin (toward the shoot apex) has also been implicated in the control of shoot branching 6. However, neither the mode of transport nor a developmental role has been shown for basipetal transport of cytokinin (toward the root apex). In this paper, we combine the use of a new technology that blocks symplastic connections in the phloem with a novel approach to visualize radiolabeled hormones in planta to examine the basipetal transport of cytokinin. We show that this occurs through symplastic connections in the phloem. The reduction of cytokinin levels in the phloem leads to a destabilization of the root vascular pattern in a manner similar to mutants affected in auxin transport or cytokinin signaling 7. Together, our results demonstrate a role for long-distance basipetal transport of cytokinin in controlling polar auxin transport and maintaining the vascular pattern in the root meristem.
► Cytokinin is transported through symplastic connections in the phloem ► Basipetal cytokinin transport regulates PIN proteins in the proximal meristem ► Basipetal cytokinin transport maintains vascular pattern in the root meristem ► Transport of specific cytokinin species could target particular developmental pathways
The formation of wood and its control Zhang, Jing; Nieminen, Kaisa; Serra, Juan Antonio Alonso ...
Current opinion in plant biology,
February 2014, 2014-Feb, 2014-02-00, 20140201, Letnik:
17
Journal Article
Recenzirano
Odprti dostop
•We compare various experimental systems for wood formation study.•We highlight the importance of the first released genome of a gymnosperm tree.•Evidence gained from Arabidopsis supports our study ...of wood formation in trees.•Knowledge on regulation of wood formation is addressed from an evo-devo perspective.
Wood continues to increase in importance as a sustainable source of energy and shelter. Wood formation is a dynamic process derived from plant secondary (radial) growth. Several experimental systems have been employed to study wood formation and its regulation. The use of genetic manipulation approaches and genome-wide analyses in model plants have significantly advanced our understanding of wood formation. In this review, we provide an update of our knowledge of the genetic and hormonal regulation of wood formation based on research in different plants systems, as well as considering the subject from an evo-devo perspective.
Sieve pores of the sieve plates connect neighboring sieve elements to form the conducting sieve tubes of the phloem. Sieve pores are critical for phloem function. From the 1950s onwards, when ...electron microscopes became increasingly available, the study of their formation had been a pillar of phloem research. More recent work on sieve elements instead has largely focused on sieve tube hydraulics, phylogeny, and eco-physiology. Additionally, advanced molecular and genetic tools available for the model species
helped decipher several key regulatory mechanisms of early phloem development. Yet, the downstream differentiation processes which form the conductive sieve tube are still largely unknown, and our understanding of sieve pore formation has only moderately progressed. Here, we summarize our current knowledge on sieve pore formation and present relevant recent advances in related fields such as sieve element evolution, physiology, and plasmodesmata formation.
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