Floral homeotic C function genes repress specific B function genes in the carpel whorl of the basal eudicot California poppy (Eschscholzia californica)

<p>Abstract</p> <p>Background</p> <p>The floral homeotic C function gene <it>AGAMOUS </it>(<it>AG</it>) confers stamen and carpel identity and is involved in the regulation of floral meristem termination in <it>Arabidopsis</it>. <it>Arabidopsis ag </it>mutants show complete homeotic conversions of stamens into petals and carpels into sepals as well as indeterminacy of the floral meristem. Gene function analysis in model core eudicots and the monocots rice and maize suggest a conserved function for <it>AG </it>homologs in angiosperms. At the same time gene phylogenies reveal a complex history of gene duplications and repeated subfunctionalization of paralogs.</p> <p>Results</p> <p><it>EScaAG1 </it>and <it>EScaAG2</it>, duplicate <it>AG </it>homologs in the basal eudicot <it>Eschscholzia californica </it>show a high degree of similarity in sequence and expression, although <it>EScaAG2 </it>expression is lower than <it>EScaAG1 </it>expression. Functional studies employing virus-induced gene silencing (VIGS) demonstrate that knock down of <it>EScaAG1 </it>and <it>2 </it>function leads to homeotic conversion of stamens into petaloid structures and defects in floral meristem termination. However, carpels are transformed into petaloid organs rather than sepaloid structures. We also show that a reduction of <it>EScaAG1 </it>and <it>EScaAG2 </it>expression leads to significantly increased expression of a subset of floral homeotic B genes.</p> <p>Conclusions</p> <p>This work presents expression and functional analysis of the two basal eudicot <it>AG </it>homologs. The reduction of <it>EScaAG1 </it>and <it>2 </it>functions results in the change of stamen to petal identity and a transformation of the central whorl organ identity from carpel into petal identity. Petal identity requires the presence of the floral homeotic B function and our results show that the expression of a subset of B function genes extends into the central whorl when the C function is reduced. We propose a model for the evolution of B function regulation by C function suggesting that the mode of B function gene regulation found in <it>Eschscholzia </it>is ancestral and the C-independent regulation as found in <it>Arabidopsis </it>is evolutionarily derived.</p

Floral homeotic C function genes repress specific B function genes in the carpel whorl of the basal eudicot California poppy (Eschscholzia californica)

<p>Abstract</p> <p>Background</p> <p>The floral homeotic C function gene <it>AGAMOUS </it>(<it>AG</it>) confers stamen and carpel identity and is involved in the regulation of floral meristem termination in <it>Arabidopsis</it>. <it>Arabidopsis ag </it>mutants show complete homeotic conversions of stamens into petals and carpels into sepals as well as indeterminacy of the floral meristem. Gene function analysis in model core eudicots and the monocots rice and maize suggest a conserved function for <it>AG </it>homologs in angiosperms. At the same time gene phylogenies reveal a complex history of gene duplications and repeated subfunctionalization of paralogs.</p> <p>Results</p> <p><it>EScaAG1 </it>and <it>EScaAG2</it>, duplicate <it>AG </it>homologs in the basal eudicot <it>Eschscholzia californica </it>show a high degree of similarity in sequence and expression, although <it>EScaAG2 </it>expression is lower than <it>EScaAG1 </it>expression. Functional studies employing virus-induced gene silencing (VIGS) demonstrate that knock down of <it>EScaAG1 </it>and <it>2 </it>function leads to homeotic conversion of stamens into petaloid structures and defects in floral meristem termination. However, carpels are transformed into petaloid organs rather than sepaloid structures. We also show that a reduction of <it>EScaAG1 </it>and <it>EScaAG2 </it>expression leads to significantly increased expression of a subset of floral homeotic B genes.</p> <p>Conclusions</p> <p>This work presents expression and functional analysis of the two basal eudicot <it>AG </it>homologs. The reduction of <it>EScaAG1 </it>and <it>2 </it>functions results in the change of stamen to petal identity and a transformation of the central whorl organ identity from carpel into petal identity. Petal identity requires the presence of the floral homeotic B function and our results show that the expression of a subset of B function genes extends into the central whorl when the C function is reduced. We propose a model for the evolution of B function regulation by C function suggesting that the mode of B function gene regulation found in <it>Eschscholzia </it>is ancestral and the C-independent regulation as found in <it>Arabidopsis </it>is evolutionarily derived.</p