Morphology, anatomy and cytology of ferns
Cell wall diversity and evolution
Sterile (left) and fertile (right) sporofyte
Sterile lamina with proliferous bud
Fertile lamina with enrolled margins
Transverse section through the petiole
Hermaphrodite (left) and male (right) gametophytes
LM11 (anti-xylan) labelling in the petiole
LM11 (anti-xylan) in the root
Gametophyte surface with antheridia
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Detailed studies focused on plant model systems such as Arabidopsis thaliana (flowering plants, angiosperms) have extensively increased our insights into plant developmental and physiological processes. During the last few decades, driven by the interest in evolutionary developmental biology, new plant model systems such as Physcomitrella patens (bryophytes), Selaginella moellendorffii (lycophytes) and Ceratopteris richardii (‘C-Fern’, ferns) have emerged. Although its genome is not yet fully sequenced, the advantages of using C-Fern as a fern model system are mainly derived from its low maintenance, and its rapid gametophyte development and life cycle.
C-Fern is a specially derived cultivar of a tropical fern, Ceratopteris richardii. Over a three-week period, C-Fern develops from a single-celled spore into a complex vascular plant with leaves and roots. This transition involves a wide range of biological phenomena, including alternation of haploid and diploid generations, differentiation of distinct gametophyte sexes and fertilization by swimming sperm. Ceratopteris possesses a short upright rhizome and grows as an annual. The fronds are dimorphic. Initial fronds are sterile and simple to 3-lobed but as development proceeds the fronds become increasingly more dissected and fertile. Sporangia are found in continuous rows on veins along the ventral edges of fertile fronds and are covered by the inrolled margin of the frond, forming a false indusium. In addition to sexual reproduction by meiotic production of spores and subsequent gametophytes, Ceratopteris sporophytes have a prolific capacity for vegetative reproduction. The buds are a convenient means of vegetatively propagating particular genotypes [see Hickok, Warne and Fribourg. 1995. The biology of the fern Ceratopteris amd its use as a model system. International Journal of Plant Science 156: 332-345].
Features which make Ceratopteris a suitable model include:
(1) a short sexual life cycle which can be completed in under 120 days,
(2) continuous and abundant spore production,
(3) spores that can be stored and remain viable for many years,
(4) gametophytes which can be self-fertilized to generate completely homozygous sporophytes,
(5) visible microtubule organizing centers and developmental synchrony of cells
within a single gametophyte
(6) sporophytes that can be vegetatively propagated from leaf buds or gemmae allowing maintenance of even sterile mutants, and,
(7) amenability to mutagenesis.
Furthermore,although experiments initially suggested that Ceratopteris is resistant to Agrobacterium-mediatedtransformation, Agrobacterium has now been shown capable of transforming Ceratopteris thalictroides spores leading to stably transformed plants; inheritance analyses revealed stable expression of the transgene in second generation sporophytes [see Muthukumar et al.2013. Stable transformation of ferns using spores as targets: Pteris vittata and Ceratopteris thalicroides. Plant Physiology 163: 648-658].
Our C-Fern research aims to investigate how cell walls are remodeled during sporophyte leaf and root development, and how the cell wall composition of the sporophyte differs from that of the gametophyte. Although the gametophyte and sporophyte share the same genetic constitution derived from the same organism, they display clear functional and morphological differences. It will be of particular interest to examine if specific cell wall polymers that are associated with complex tissues or structures in the sporophyte are also present in the morphologically simple (parenchymatous) gametophyte. These preliminary studies may deepen our understanding of how cell wall polymers and their structural variants are associated with the development and evolution of cell types, tissues and diverse plant morphologies.
Dr. Zoë A. Popper (National University of Ireland, Ireland)
Prof. Dr. William Willats (University of Copenhagen, Denmark)
Prof. Dr. Alexandra A. Mastroberti (Universidade Federal do Rio Grande do Sul, Brazil)
Leroux O., Eeckhout S., Viane R.L.L., Popper Z.A. 2013. Ceratopteris richardii (C-Fern): a model for investigating adaptive modification of vascular plant cell walls. Frontiers in Plant Sciences. Plant Evolution and Development 4, 367.