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Abstract Detail

Fossil plants at the intersection of evo-devo and phylogeny: celebrating the contributions of Gar W. Rothwell to biodiversity and evolution

Tomescu, Alexandru M.F. [1].

Whence secondary growth? Outlining a research agenda.

Surveying extant plant diversity, one is easily (mis)led to recognizing secondary growth with wood production as an exclusive attribute of seed plants. However, studies of the fossil record have documented secondary xylem in multiple distinct lineages: lycopsids, cladoxylopsids, sphenopsids, zygopterid ferns s.l., stenokolealeans, progymnosperms. Such paleobotanical datapoints placed the origins of secondary xylem in different lineages throughout the Middle Devonian-early Carboniferous interval and led to the traditional view that wood evolved independently multiple times. Recently, paleobotany has returned with diverse evidence for woody growth in the deeper, Early Devonian fossil record. These discoveries blur the traditional image, raising the possibility of a single common origin of secondary growth, at least within the euphyllophyte clade. Addressing this hypothesis requires a set of convergent approaches. One of these approaches involves characterizing wood production from a vascular cambium as a system of modular component processes working within a set of anatomical constraints, a view supported by observational and experimental evidence from fossil and living plants, and uncovering the molecular-genetic regulation of these processes. A short list of such processes includes assembly of a cambial layer and maintenance of meristematic identity; periclinal divisions of cambial initials - their initiation, control of the plane of cell division, and synchronization; establishment of identity of secondary tissues produced on either side of the cambium; anticlinal divisions of cambial initials - their initiation, control of cell division plane, and symmetry (or lack thereof). Although regulatory networks for these processes can only be characterized in detail in living seed plants, presence and functions of such regulators have been or can be documented in non-woody living lineages. Such information can provide hypotheses on a potential shared developmental toolkit for wood production and variations in its processual range across the breadth and depth of plant phylogeny. A second path toward understanding the origins of woody growth involves assessment of the various fossil occurrences of secondary xylem, with the aim of characterizing their anatomy in detail within a comparative developmental framework. At the convergence of these two approaches lies reciprocal illumination. Integration of their information in a phylogenetic and stratigraphic framework could lead to identification of anatomical fingerprints for the modular processes of secondary growth and their regulatory mechanisms; documenting the phylogenetic spread of these processes and mechanisms; and reconciling these with hypotheses on the extent and evolution of the toolkit for secondary growth gleaned from developmental-molecular data on living plants.

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1 - Humboldt State University, Department of Biological Sciences, 1 Harpst Street, 1 Harpst Street HSU - Biology, Arcata, California, 95521, USA, 7078263229

secondary growth
secondary xylem
fossil record
evolution of development
developmental anatomy
Wood anatomy
vascular cambium

Presentation Type: Colloquium Presentations
Session: C11b, Fossil plants at the intersection of evo-devo and phylogeny: celebrating the contributions of Gar W. Rothwell to biodiverstiy and evolution Part 2
Location: 110/Mayo Civic Center
Date: Wednesday, July 25th, 2018
Time: 2:15 PM
Number: C11b002
Abstract ID:672
Candidate for Awards:None

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