Relationships and reproduction — Floral development and phylogeny in Australian sedges (Cyperaceae, Mapanioideae): implications for the evolution of the monocot flower

A project undertaken at Botany, School of Environmental and Rural Science, University of New England and supervised by Jeremy Bruhl

This project is the subject of a PhD project by Chrissie Prychid at UNE, supervised by Jeremy Bruhl (UNE) and David Simpson (Royal Botanic Gardens Kew)


Flowering plants are one of the most successfully diverse groups of organsims on the planet, yet highly conserved molecular mechanisms result in flowers with just four distinct organ types, arranged on a specific architectural plan. Studies within Arabidopsis and Antirrhinum, have yielded the ‘ABCDE’ model of flower development to explain the specification of organ identities. Development of many flowers, however, cannot be reconciled with this model. Only by expanding our studies will we be able to test the general validity of the model or determine which parts are species/genera/family specific.


Cyperaceae with c. 5,400 species and 106 genera (Bruhl 1995; Govaerts et al. 2007) are the third largest family of monocots, after the orchids and grasses, and seventh largest of the angiosperms, yet remain poorly known and are considered difficult, largely due to problems with the uncertain character homology of their diverse, sometimes complex and highly reduced flowers or reproductive units. Molecular phylogenetic analyses of Cyperaceae recover two subfamilies: the Mapanioideae and the Cyperoideae (Simpson et al. 2003; Simpson et al. 2007). However, in the most recent analyses, relationships within the Mapanioideae were still largely unresolved (Muasya et al. 2009).


Historical interpretations, following either euanthial or synanthial hypotheses, of the reproductive units within the family remain controversial. However, it is generally accepted that the subfamily Cyperoideae (and Juncaceae, sister family to Cyperaceae) mostly have typical trimerous monocot flowers (i.e. with the flower parts in threes or multiples of three); the perianth segments when present are bristles or scales. In the little-known Australian mapaniid sedges (Cyperaceae subfam. Mapanioideae) though, there are considerable discrepancies between the standard floral architecture one would expect and what one sees, to the extent that we are still asking “just what is a flower?”. Mapaniid intricate floral and inflorescence (spikelet) morphologies have seen the reproductive units considered as modified flowers or reduced inflorescences (see Bruhl 1991), or even possible ‘hybrid’ structures (Prychid et al. 2011, Prychid & Bruhl in press).


Within the mapaniids there has been relatively little work done on determining floral developmental homologies, particularly using organ inititiation sequence pattern data, a technique useful for flowers with unusual dispositions of organs (Hufford 2003). Also, the genes and the genetic mechanisms involved in the formation of the unique mapaniid reproductive morphologies are almost unknown. We have used the only currently available reproductive gene sequence known for Cyperaceae Cyl-FUL, the AP1-FUL-like gene of Cyperus longus (Cyperaceae subfam. Cyperoideae) as a probe to resolve some of the questions in the mapaniid genus Lepironia (Prychid & Bruhl in press) and we further aim to integrate new data on phylogeny, developmental morphology and genetics to understand the origins and diversity of the mapaniid floral form. Our study will result in important immediate contributions to knowledge of floral evolution, cytological evolution, species relationships and biogeography.


Specific Aims
  1. To reconstruct mapaniid evolutionary relationships via combined multigene and morphological analyses, to understand and interpret floral character homology in these uniquely different taxa.
  2. To obtain novel ontogenetic data on the development of the floral structures. Develop a strong understanding of floral pattern formation by undertaking extensively detailed microscopical observations of developing taxa, which will yield a series of ‘landmarks’ to designate key stages of floral development.
  3. To determine genome sizes and ploidy levels across key taxa in relation to species, lineage and floral diversity.
  4. To determine the genetic controls responsible for dramatically altering the floral form and assess evolutionary relationships and changes in function of specific floral regulatory protein and gene families.
  5. To develop and apply tools for the first comparative assessment of floral gene expression in mapaniids. To develop a new method for 3-D visualisation of spatio-temporal gene expression maps using x-ray tomography (XRT).
References
Bruhl JJ. 1991. Aust J Bot 39: 119-127
Bruhl JJ. 1995. Aust J Bot 8: 125-305
Govaerts R, Simpson DA, Bruhl J, Egorova T, Goetghebeur P. & Wilson K. 2007. World checklist of Cyperaceae Sedges. Royal Botanic Gardens, Kew; Hufford L. 2003. Int J Pl Sci 164: S409-439
Muasya AM, Simpson DA, Verboom GA. et al. 2009. Bot Rev 75: 2-21
Prychid CJ, Bruhl JJ, Vrijdaghs A. & Reynders M. 2011. In ‘IBC’ (Melbourne)
Prychid CJ & Bruhl JJ. (in press) Ann Bot
Simpson DA, Furness CA, Hodkinson TR, Muasya AM. & Chase MW. 2003. Am J Bot 90: 1071-1086
Simpson DA, Muasya AM, Alves M, Bruhl JJ, Dhooge S, Chase MW, Furness CA, Ghamkhar K, Goetghebeur P, Hodkinson TR, Marchant AD, Reznicek AA, Nieuwborg R, Roalson EA, Smets E, Starr JR, Thomas WW, Wilson KL. & Zhang X. 2007. Aliso 23: 72-83.


Figure 1. Jeremy Bruhl collecting fertile samples of Mapania sumatrana in north Queensland (photo: CJP)

 

Figure 2. Chrissie Prychid photographing Chrysitrix distigmatosa in Western Australia (photo: JJB)

 

Figure 3. Inflorescence of Chrysitrix distigmatosa in male phase (photo: JJB)

 

Figure 4. Inflorescence of Chorizandra spaerocephala collected in NSW, in cultivation at UNE (photo: JJB)