Plant Genome II Conference
Town & Country Conference Center, San Diego, CA, January, 1994.
PG-II: GRASSES AS A SINGLE GENETIC SYSTEM: LIGULES AND TRANSPOSON MU
GRASSES AS A SINGLE GENETIC SYSTEM: LIGULES AND TRANSPOSON MU
Michael Freeling and laboratory, Department of Plant Biology,
University of California, Berkeley, CA 94720
In the grasses -- and in other taxa as well -- innovations
in wide sexual hybridizations, DNA transformation, coupled with
detailed RFLP map comparisons demonstrating genome coliniarity
(see Bennetzen and Freeling, 1993, TIGS 9:259; Moore et al.,
1993, BioTech. 11:584; Ahn and Tanksley, 1993, PNAS 90:7980) are
changing the fundamental applicability of the genetic approach to
biological problems. The ca. 12,000 species of grasses have
vegetative leaves in two parts, a proximal sheath and a blade.
Between sheath and blade is a boundary. In maize, this boundary
is called the ligular region. A mature maize leaf has a
membranous, epidermal ligule and wedge-like auricles at this
boundary. In rice, the auricles are extended into horns and the
ligule is a true organ with veins, stomata, and other leaf-like
characters. In both species, recessive mutants remove these
ligule/auricle elaborations, but no grass or mutant grass is
missing the boundary itself. We have established a cascade of
gene product function in maize. (see general review Freeling,
Develop. Biol., 1992, 153:44). By map location and DNA sequence
homology, we will soon clone homologs in other grasses with
morphologically different ligule/auricles. By combinations of
wide crosses and DNA transformation, we can now partition ligular
region morphological differences to genes and gene sequence.
Many characters in plants might now be appropriately studied
using a pan-grass approach. I will also review a
similar pan-grass approach involving the autonomous Mu transposon
of maize: Mud-1 (see review: Chandler & Hardenian, 1993,
Advances in Genetics 30:77). We know that sequences similar to
this transposon exist in many grasses, but function remains
elusive.
Return to Previous Page or Intl-PAG Homepage