Monocot Pollen Evolution
Recent improved phylogenies of the monocotyledons utilising molecular data have allowed a re-assessment of key pollen and anther characters within the group. This is a long-term project, ongoing since 1995. The aims are (1) to review pollen and anther characters of systematic significance throughout the monocots, e.g. tapetum type, microsporogenesis, inaperturate pollen, and (2) to target specific groups for more detailed study. Research techniques include light microscopy and both scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Most plant material for research comes from the Kew living collections, and some from the Herbarium.
A major focus since 2006 has been pollen evolution in the early-divergent monocot order Alismatales. Phylogenetic mapping of pollen and tapetum characters demonstates that Alismatales are characterized by a potential synapomorphy: a plasmodial tapetum. Linked character syndromes, involving thin-walled or exineless, inaperturate (omniaperturate) pollen with a smooth or exineless surface, have evolved iteratively within the order, probably related to the aquatic or semiaquatic habit of many alismatids.
A second focus has been comparative studies on the highly unusual pattern of pollen development, involving selective microspore abortion producing pseudomonads (termed monomicrospory), that occurs in sedges (Cyperaceae) and the epacrid subfamily of the eudicot family Ericaceae (see Large Scale Syntheses: Pollen Evolution). Our comparison of these two examples of selective microspore abortion highlights a correlation with aneuploidy, indicating that non-random chromosome segregation caused by monomicrospory could drive chromosomal mutations to rapid fixation through meiotic drive.
We have continued our interest in microsporogenesis in monocots, shown to be of systematic significance in our pre-2006 work, e.g. Furness and Rudall (1999). Firstly, a collaboration with a research group at Université Paris-Sud has led to a paper presenting the first broad overview of three main features of microsporogenesis in angiosperms, with a focus on monocots: cytokinesis, intersporal wall formation, and tetrad form. A phylogenetic comparative approach was used to test for correlated evolution among these characters and to make hypotheses about evolutionary trends in microsporogenesis. Secondly, work with Graça Sajo, a Brazilian collaborator, led to the first description of simultaneous microsporogenesis in a grass, Streptochaeta spicata Schrad.
An interest in pollen of Dioscorea (Dioscoreales) has also been maintained, building on pre-2006 work, and contributing to the delimitation of a new species of yam from Kenya, Dioscorea kituiensis Wilkin & Muasya.
The outputs of the project are published in peer-reviewed journals, and books, and presented at international conferences.
Reference: Furness, C. A. & Rudall, P. J. (1999). Microsporogenesis in monocotyledons. Annals of Botany 84: 475-499.
Project partners and collaborators
Universidade Estadual Paulista, São Paulo