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Abstract Detail

Evolutionary Developmental Biology (Evo-Devo)

Hearn , David John [1].

Reaction-diffusion model of plant serial homology development and implications in plant evolutionary-developmental biology.

A deeper understanding of processes responsible for modularity and the serial homology it entails is central to a more complete picture of plant evolution and development. Most land plants are built from basic, serially homologous units, such as leaves and internode-node-bud rametes. As iterated features, supplemental vascular bundles (SVBs) that occur independently of the vascular stele are underappreciated components of this recurrent, serial homology picturen of plant development.  SVBs evolved repeatedly in a wide diversity of angiosperm taxa. They tend to evolve in tandem with evolutionary increases in parenchyma storage tissues and are implicated in distributing resources within these putatively diffusion limited structures. Within parenchymatous roots and shoots, SVBs are often uniformly distributed, forming a spotted pattern in cross section and a matrix of longitudinally-oriented vessels in longitudinal section. To understand the pattern formation mechanisms responsible for SVBs in parenchymatous roots and shoots, a spatially explicit, 3D, stochastic reaction-diffusion system was used to model the spatial and temporal development of SVBs. The model includes an activator-inhibitor pair and a third participant that itself inhibits the other inhibitor. It is hypothesized that this trio corresponds to the genes HB8, BR, and mi165; HB8 and BR were previously found to be differentially expressed in parenchymatous woods and are implicated in vascular meristem initiation and differentiation, whereas mi165 is a posttranscriptional suppressor of members of the REVOLUTA family that includes HB8. This relatively simple model of three components recreates empirical SVB patterns. The model produces SVBs in centers of wide parenchymatous regions in regular arrays. Parenchymatous regions that are too narrow fail to produce the SVBs. Diffusion rates of the three model components influence the number and size of the SVBs. As protein size is directly related to cytosolic diffusion rate through the Einstein-Stokes equation, these results have broad-ranging implications for the evolution of serially homologous structures. First, the cessation of development of SVBs below a threshold width of parenchymatous tissues suggests that some characters may be lost during evolution not because of changes to the genes directly involved in the characters’ development, but rather due to changes in the morphological context in which development takes place. Second, size and number of serially homologous structures can have more to do with changes in the size of proteins regulating their development than evolutionary changes to the molecular functions of the proteins themselves.

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1 - Towson University, 8000 York Road, Towson, MD, 21252, USA

serial homology
plant succulence
supplemental vascular bundle
pattern formation
activator-inhibitor dynamics.

Presentation Type: Oral Paper:Papers for Topics
Session: 46
Location: Payette/Boise Centre
Date: Wednesday, July 30th, 2014
Time: 3:45 PM
Number: 46001
Abstract ID:674
Candidate for Awards:None

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