Abstract Detail

Novel Approaches to Plant Evolution from Paleontological, Physiological, and Developmental Perspectives

Wilson, Jonathan P. [1], Trembath-Reichert, Elizabeth [2], McGlynn, Shawn E. [3], Fischer, Woodward W. [4].

A molecular and geobiological perspective on the evolution of plant biomineralization.

Many plants produce deposits of amorphous silica within their tissues.. Although the biological function(s) of silica phases has not been tested for every plant, they are believed to confer mechanical support to plants, increase resistance to damage by pathogens, and deter grazing by herbivores. The phylogenetic distribution and biosynthesis of silica has been primarily studied in monocot angiosperms (e.g., grasses), but the origin of this biomineralization process and its early evolutionary history remain poorly known, with limited paleontological data that can be brought to bear on plant silica’s early history.
We investigated the evolution of silica biomineralization by employing a combined geochemical and molecular comparative biology approach across a deeper diversity of living land plants, with explicit focus on groups with long evolutionary histories that were once far more common in terrestrial ecosystems. We measured silica abundance within photosynthetic tissues collected from a large and diverse suite of wild and cultivated plants collected throughout Southern California using a modified dry-ashing technique, and then imaged the resulting silica biominerals using electron microscopy and energy dispersive spectroscopy. Results show silica abundance is very high in early-diverging plant groups like eusporangiate ferns and sphenopsids, including some bryophytes; these values are as high or higher on average than many silica-bearing monocot grasses. However, conifers and cycads are low. We combined these observations with data and analyses from the molecular and structural biology of silicic acid transport proteins, which are the biochemical gatekeepers for silica entry into plant tissues. Our analyses show that silicic acid transporters are derived within a group of nodulin-26-like modified aquaporins and, within angiosperms, silicic acid transporters appear to have a single origin descended from a group of arsenite and glycerol transporters present in the earliest embryophytes. Analysis of silicic acid transporter homologues illustrates multiple origins of silica biomineralization within non-angiosperm silicic acid transporters, including independent origins within lycopsids and Equisetum. No porins with possible silicic acid transport function have been identified in conifers, despite several complete genomes of conifer species, which supports the observation that silica biominerals are comparatively rare within conifers and environmental variation in silica abundance is common.
Altogether these results illustrate that silica biomineralization was both a feature of early land plants, and perhaps evolved several times again within the seed plants. Most notably, silica cycling in terrestrial ecosystems was likely an important process during the Paleozoic Era, when lycopsids, ferns, and horsetails were abundant and diverse.

1 - Haverford College, Department Of Biology, 370 Lancaster Ave, Haverford, PA, 19041, USA
2 - California Institute of Technology, Geological and Planetary Sciences, 1200 E. California Blvd., Pasadena, CA, 91125, USA
3 - Tokyo Institute of Technology, Earth-Life Science Institute, 2-12-1-IE-1 Ookayama, Meguro-ku, Tokyo, 152-8550, Japan
4 - California Institute of Technology, Geological and Planetary Sciences, 1200 E. California Blvd., Pasadena, CA, 91125, United States

Keywords:
biomineralization
phytolith
silicic acid
silica cycle
NIP superfamily.

Presentation Type: Symposium Presentation
Session: SY11, Novel approaches to plant evolution from paleontological, physiological, and developmental perspectives
Location: 101/Savannah International Trade and Convention Center
Date: Wednesday, August 3rd, 2016
Time: 5:15 PM
Number: SY11009
Abstract ID:805
Candidate for Awards:None