MALCOMBER, SIMON T.*, ANDREW N. DOUST, TONY VERBOOM, and ELIZABETH A. KELLOGG. Dept. Biology, R 223, University of Missouri-St. Louis, 8001 Natural Bridge Road, St. Louis, MO 63121, USA. - Nucleotide and amino acid sequence evolution of tassleseed2 in Poaceae and implications for estimated secondary protein structure.
Unisexual flowers have evolved multiple times within Poaceae in such
diverse lineages as Bambusoideae, Ehrhartoideae, Pooideae,
Danthonieae, Chloridoideae and Panicoideae. The conversion from a
bisexual to unisexual floral meristem in Zea mays is correlated
with programmed cell death and the expression of tassleseed2
(ts2). Based on developmental studies, ts2 is hypothesized
to act in a similar manner in other panicoid grasses. Little is known
about the genetic basis of unisexual flowers in other grass lineages,
although developmental studies in Zizania aquatica suggest that
either ts2 is not involved in the production of male flowers or
is regulated differently. We have designed primers to amplify a 550 bp
fragment at the 3’ end of the ts2 gene for a phylogenetically
diverse array of grasses. Preliminary results suggest that ts2
sequence is largely conserved within Panicoideae (nucleotide
divergence 3.1-6.1%, amino acid divergence 1.7-6.5%) and Bambusoideae
(nucleotide divergence 6.2%, amino acid divergence 4.7%), but less so
within Ehrhartoideae (nucleotide divergence 17.1% amino acid
divergence 16.5%), largely due to the Zizania sequence.
Nucleotide sequence divergence between Oryza and Bambusoideae
(7.8-9.5%) and Panicoideae (7.8-9.5%) taxa, is less than the estimated
divergence between Oryza and Zizania. A hot spot of
sequence evolution in all sampled taxa occurs between amino acids 255
and 270 of the Zea mays ts2 protein. Zizania has a
large deletion within this area that maps to a helix in the estimated
secondary protein structure. Other aspects of how amino acid sequence
evolution affects estimated secondary protein structure will be
discussed within the context of the GWPG phylogeny.
Key words: developmental genes, Poaceae