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Plant development and evolution: Lessons learned from candidate genes

Whipple, Clinton [1], Ciceri, Pietro [1], Schmidt, Robert [1].

Conservation Between Maize and Arabidopsis B-class gene Function.

Analyses of core eudicot B-class mutants strongly support a central role for B-class genes in controlling stamen and petal identity in this group. Expression analysis in other lineages including basal eudicots, however, suggests that B-class homeotic control of petal identity may not be strictly conserved across the angiosperms more broadly. Well characterized B-class mutants in maize and rice show that in the grasses, B-class genes control stamen and lodicule identity, raising the possibility that lodicules represent modified petals, and B-class function is conserved between monocots and eudicots. In order to further test the hypothesis of conservation of B-class function, we have used the maize AP3 ortholog (Silky1) and a PI ortholog (Zmm16) to rescue their corresponding Arabidopsis B-function mutants. We report that both maize genes, either singly or together in an ap3 pi double mutant, are capable of strongly rescuing petal and stamen development. We also have found that SILKY1 and ZMM16 proteins bind DNA as an obligate heterodimer as do the Arabidopsis AP3 and PI, further supporting conservation of biochemical function of B-class genes. In order to test the hypothesis that lodicules represent modified second whorl petals, we have begun isolating B-class genes from basal grass species as well as close outgroups, that have clear petals or tepals in their second whorl. In situ analysis of a PI ortholog in Streptochaeta, a basal grass having no lodicules but specialized foliar organs in their position, unambiguously shows expression in stamens and these second whorl organs. This finding supports the interpretation of lodicules as modified petals, and further supports a conserved role for B-class genes in specifying second and third whorl organ identity between monocots and eudicots. In situ expression analysis on other species is underway to further test this hypothesis.

1 - Universtiy of California -- San Diego, Division of Biology, Section of Cell and Developme, 9500 Gilman Drive, La Jolla, California, 92093-0116, USA

ABC model
flower development
MADS box genes

Presentation Type: Symposium
Session: 54-5
Location: Ballroom 1 (Cliff Lodge)
Date: Wednesday, August 4th, 2004
Time: 3:00 PM
Abstract ID:179

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