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Abstract Detail

Development and Structure

Di Stilio, Veronica [1], San Martin, Juca [2], Pozner, Raul [2], Nolan, Christine [1].

A structural model for a key innovation in seed plant reproduction: Fleshy diaspores in the gymnosperm Ephedra (Gnetales).

Plants are sessile organisms with limited opportunities for gene flow, with seeds representing a major innovation that enabled long-distance dispersal of the dormant embryo. Structures other than the angiosperm ovary can perform comparable functions in gymnosperm seed dispersal. While understanding of the anatomical, developmental, and genetic basis of angiosperm fleshy fruits is fairly advanced, much less is known about the analogous role that fleshy structures play in gymnosperm seed dispersal. We investigate the evolution and development of fleshy structures with fruit-like function in Ephedra (Gnetales), shrubs and vines of arid and semi-arid regions with fleshy and non-fleshy diaspores dispersed by animals or wind. Ephedra cone bracts are modified leaves that surround and sometimes fuse around the ovule and may become fleshy, performing an analogous function to that of the ovary that becomes fleshy in certain angiosperm fruits. The South American Ephedra clade captures the diversity in seed accessory structures: sister species E. triandra and E. tweediana are diploid climbing shrubs with fleshy red seed cone dispersed mainly by birds, E. chilensis has partially fused and fleshy orange bracts and tetraploid E. multiflora is a wind-dispersed high-elevation species with papery winged seed bracts. With the overall goal of better understanding the structural and genetic mechanisms underlying the fleshy bract character in Ephedra seed dispersal units, we ask: (a) What is the developmental and genetic basis of seed cone bract fleshiness? (b) How does the anatomy of fleshy seed cone bracts compare to that of non-fleshy bracts, and leaves? To answer these questions, we performed ontogenetic observations, anatomical sections, biochemical assays, and differential gene expression analysis by RNAseq. Our preliminary findings suggest that leaf anatomy is similar in all species, fleshiness of female cone bracts is based on chlorenchyma muciniferous cells that are present since early developmental stages in fleshy species only, and that cellulosic fibers, known to be involved in apoplastic water transport, proliferate during the development of cone bracts and leaves. We identify differentially expressed genes in E. triandra as bracts swell and become fleshy, including the downregulation of a glycoside hydrolase involved in breaking down polysaccharides, and the upregulation of pectate lyase (pectin degradation) and DUF642 domain-containing proteins (regulation of cell wall properties). In conclusion, we propose a structural and evolutionary model of fleshy vs. papery-winged bract development in four species of Ephedra and speculate on the potential role of differentially expressed genes.

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1 - University of Washington, Department of Biology, P.O. Box 351800, Seattle, WA, 98195, USA
2 - Instituto de Botánica Darwinion (IBODA, CONICET & ANCEFN), Casilla de Correo 22, Labardén 200, San Isidro, Buenos Aires, B1642HYD, Argentina

Seed Dispersal
cellulosic fibers

Presentation Type: Oral Paper
Session: DS2, Development and Structure II
Location: /
Date: Wednesday, July 21st, 2021
Time: 1:15 PM(EDT)
Number: DS2013
Abstract ID:1090
Candidate for Awards:None

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