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Abstract Detail

Kaplan Memorial Lecture - Elizabeth Kellogg

Kellogg, Elizabeth [1].

A tale of two meristems, Or, Dissecting a synapomorphy.

In the early days of phylogenetic analysis (cladistics), the search for morphological synapomorphies was central to reconstructing phylogenies. Fast forward to the early 2000s, and we now can use the phylogeny to understand morphology by identifying structures, gene networks, or processes that are unique to particular clades. The study of morphology thus becomes many-layered and defies assignment to a particular scientific subdiscipline. In this talk I present a case study from the grass tribe Andropogoneae, the most economically and ecologically important of the grasses, including maize, sorghum, and most of the dominant species of the world's C4 grasslands. Identification keys use the presence of paired spikelets as a diagnostic character for Andropogoneae. Phylogenies show that paired spikelets are shared among members of the clade but they appear in parallel elsewhere in the family. Developmentally, the paired spikelets originate from an enlarged branch meristem that converts rapidly to spikelet meristems, one sessile and one pedicellate. In Andropogoneae this branch structure is controlled by a uniquely derived genetic network. Thus the shared derived character for the tribe is not just the morphological structure but also the network that controls it. The pair is also subtended by an abscission zone, the position of which is synapomorphic for Andropogoneae s.s. In other panicoid grasses, the abscission zone forms below the spikelet and the change in position occurred before diversification of the tribe. The entire pair is thus functions as the dispersal unit. Spikelets in other panicoid grasses are generally identical in structure and function, but in the Andropogoneae spikelets of the pair partitioned the ancestral functions, with one being dedicated to seed bearing and largely encased in a hard covering (glume) and the other staminate, sterile or missing entirely. When present, the pedicellate spikelet serves as a nurse tissue providing photosynthate to the developing seed in the sessile spikelet. Because of this function, the pedicellate spikelet can be is agronomically important in cultivated species. The diagnostic - and uniquely derived - character for Andropogoneae is thus not just the pair of spikelets, but also the position of the abscission zone, the underlying genetic network, and the functions in dispersal and photosynthesis. The morphology of a simple pair of spikelets thus offers additional layers of insight into evolutionary mechanisms and potential selective forces.

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1 - Donald Danforth Plant Science Center, 975 North Warson Road, St. Louis, MO, 63132, United States

none specified

Presentation Type: Special Presentation
Session: S5, Kaplan Memorial Lecture Reception
Location: 107/Mayo Civic Center
Date: Tuesday, July 24th, 2018
Time: 3:30 PM
Number: S5001
Abstract ID:1031
Candidate for Awards:None

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