| 1. |
- Bhalerao, Rishikesh P., et al.
(author)
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Cytokinin and Auxin Display Distinct but Interconnected Distribution and Signaling Profiles to Stimulate Cambial Activity
- 2016
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In: Current Biology. - : Elsevier BV. - 0960-9822 .- 1879-0445. ; 26, s. 1990-1997
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Journal article (peer-reviewed)abstract
- Despite the crucial roles of phytohormones in plant development, comparison of the exact distribution profiles of different hormones within plant meristems has thus far remained scarce. Vascular cambium, a wide lateral meristem with an extensive developmental zonation, provides an optimal system for hormonal and genetic profiling. By taking advantage of this spatial resolution, we show here that two major phytohormones, cytokinin and auxin, display different yet partially overlapping distribution profiles across the cambium. In contrast to auxin, which has its highest concentration in the actively dividing cambial cells, cytokinins peak in the developing phloem tissue of a Populus trichocarpa stem. Gene expression patterns of cytokinin biosynthetic and signaling genes coincided with this hormonal gradient. To explore the functional significance of cytokinin signaling for cambial development, we engineered transgenic Populus tremula x tremuloides trees with an elevated cytokinin biosynthesis level. Confirming that cytokinins function as major regulators of cambial activity, these trees displayed stimulated cambial cell division activity resulting in dramatically increased (up to 80% in dry weight) production of the lignocellulosic trunk biomass. To connect the increased growth to hormonal status, we analyzed the hormone distribution and genome-wide gene expression profiles in unprecedentedly high resolution across the cambial zone. Interestingly, in addition to showing an elevated cambial cytokinin content and signaling level, the cambial auxin concentration and auxin-responsive gene expression were also increased in the transgenic trees. Our results indicate that cytokinin signaling specifies meristematic activity through a graded distribution that influences the amplitude of the cambial auxin gradient.
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| 2. |
- Helariutta, Yrjö
(author)
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Arabidopsis as a model for wood formation
- 2011
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In: Current Opinion in Biotechnology. - : Elsevier BV. - 0958-1669 .- 1879-0429. ; 22, s. 293-299
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Research review (peer-reviewed)abstract
- Wood (secondary xylem) is one of the most important sustainable energy sources for humans. Arabidopsis, despite its herbaceous nature, has become an excellent model to study wood formation. Recent progress has shown that conserved molecular mechanisms may exist in herbaceous plants and trees during vascular development and wood formation. Several transcription factor families and plant hormone species as well as other factors contribute to the regulation of xylem development in both Arabidopsis and woody plants. In this review, we highlight how information gained from the analysis of vascular development in Arabidopsis has improved our understanding of wood formation in trees.
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| 3. |
- Helariutta, Yrjö
(author)
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Cytokinin signaling during root development
- 2009
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In: International Review of Cell and Molecular Biology Volume 276. - 9780123748072 ; 276, s. 1-48
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Book chapter (peer-reviewed)abstract
- The cytokinin class of phytohormones regulates division and differentiation of plant cells. They are perceived and signaled by a phosphorelay mechanism similar to those observed in prokaryotes. Research into the components of phosphorelay had previously been marred by genetic redundancy. However, recent studies have addressed this with the creation of high-order mutants. In addition, several new elements regulating cytokinin signaling have been identified. This has uncovered many roles in diverse developmental and physiological processes. In this review, we look at these processes specifically in the context of root development. We focus on the formation and maintenance of the root apical meristem, primary and secondary vascular development, lateral root emergence and development, and root nodulation. We believe that the root is an ideal organ with which to investigate cytokinin signaling in a wider context.
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| 4. |
- Helariutta, Yrjö
(author)
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Hormone interactions during vascular development
- 2009
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In: Plant Molecular Biology. - : Springer Science and Business Media LLC. - 0167-4412 .- 1573-5028. ; 69, s. 347-360
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Journal article (peer-reviewed)abstract
- Vascular tissue in plants is unique due to its diverse and dynamic cellular patterns. Signals controlling vascular development have only recently started to emerge through biochemical, genetic, and genomic approaches in several organisms, such as Arabidopsis, Populus, and Zinnia. These signals include hormones (auxin, brassinosteroids, and cytokinins, in particular), other small regulatory molecules, their transporters, receptors, and various transcriptional regulators. In recent years it has become apparent that plant growth regulators rarely act alone, but rather their signaling pathways are interlocked in complex networks; for example, polar auxin transport (PAT) regulates vascular development during various stages and an emerging theme is its modulation by other growth regulators, depending on the developmental context. Also, several synergistic or antagonistic interactions between various growth regulators have been described. Furthermore, shoot-root interactions appear to be important for this signal integration.
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| 5. |
- Helariutta, Yrjö
(author)
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Stem cell function during plant vascular development
- 2009
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In: Seminars in Cell and Developmental Biology. - : Elsevier BV. - 1084-9521 .- 1096-3634. ; 20, s. 1097-1106
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Research review (peer-reviewed)abstract
- While many regulatory mechanisms controlling the development and function of root and shoot apical meristems have been revealed, our knowledge of similar processes in lateral meristems, including the vascular cambium, is still limited. Our understanding of even the anatomy and development of lateral meristems (procambium or vascular cambium) is still relatively incomplete, let alone their genetic regulation. Research into this particular tissue type has been mostly hindered by a lack of suitable molecular markers, as well as the fact that thus far very few mutants affecting plant secondary development have been described. The development of suitable molecular markers is a high priority in order to help define the anatomy, especially the location and identity of cambial stem cells and the developmental phases and molecular regulatory mechanisms of the cambial zone. To date, most of the advances have been obtained by studying the role of the major plant hormones in vascular development. Thus far auxin, cytokinin, gibberellin and ethylene have been implicated in regulating the maintenance and activity of cambial stem cells; the most logical question in research would be how these hormones interact during the various phases of cambial development. (C) 2009 Elsevier Ltd. All rights reserved.
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