GLOBOSA: a homeotic gene which interacts with DEFICIENS in the control of Antirrhinum floral organogenesis.

Abstract

GLOBOSA (GLO) is a homeotic gene whose mutants show sepaloid petals and carpelloid stamens. The similarity of Glo mutants to those of the DEFICIENS (DEFA) gene suggests that the two genes have comparable functions in floral morphogenesis. The GLO cDNA has been cloned by virtue of its homology to the MADS‐box, a conserved DNA‐binding domain also contained in the DEFA gene. We have determined the structure of the wild type GLO gene as well as of several glo mutant alleles which contain transposable element insertions responsible for somatic and germinal instability of Glo mutants. Analyses of the temporal and spatial expression patterns of the DEFA and GLO genes during development of wild type flowers and in flowers of various stable and unstable defA and glo alleles indicate independent induction of DEFA and GLO transcription. In contrast, organ‐specific up‐regulation of the two genes in petals and stamens depends on expression of both DEFA and GLO. In vitro DNA‐binding studies were used to demonstrate that the DEFA and GLO proteins specifically bind, as a heterodimer, to motifs in the promoters of both genes. A model is presented which proposes both combinatorial and cross‐regulatory interactions between the DEFA and GLO genes during petal and stamen organogenesis in the second and third whorls of the flower. The function of the two genes controlling determinate growth of the floral meristem is also discussed.

The whorl‐specific action of a petunia class B floral homeotic gene

“…In Arabidopsis and Antirrhinum, genes class A, B and C have been identi®ed (Yanofsky et al 1990;Sommer et al 1990;Jack et al 1992;Mandel et al 1992;Trobner et al 1992;Bradley et al 1993;Goto & Meyerowitz 1994;Jofuku et al 1994). Most of these genes encode proteins with a conserved DNA-binding domain, the MADS box.…”

“…The products of two Arabidopsis class B genes, AP3 and PI, or two Antirrhinum class B genes, DEF and GLO, have been shown in vitro to form a heterodimer. The heterodimers positively regulate the expression of their own genes (Schwarz-Sommer et al 1992;Trobner et al 1992;Goto & Meyerowitz 1994).…”

Arabidopsis floral homeotic gene BELL (BEL1) controls ovule development through negative regulation of AGAMOUS gene (AG).

“…In Arabidopsis, at least five genes-APETALA1 (API), AP-ETALA2 (AP2), APETALA3 (AP3), PISTILLATA (PI), and AGAMOUS (AG)-are responsible for this determination (5,(8)(9)(10)(11). Several of these genes have now been cloned and found to be homologous to known transcription factors identified in yeast and mammals (12)(13)(14)(15). One of these genes, AG, important for carpel identity (5,8,16), is also potentially involved in ovule development.…”

Cell-cell interactions during plant development.

“…Both def and globosa (glo) are required for the identity of floral organs in the second and third whorl floral organs; petals are replaced by sepals and stamens have carpel identity in def or glo mutant plants (Sommer et al 1990;Schwarz-Sommer et al 1992;Tr6bner et al 1992). glo and def are induced independently but require each other for upregulation; in the absence of one protein, the other protein is missing Tr6bner et al 1992).…”

“…glo and def are induced independently but require each other for upregulation; in the absence of one protein, the other protein is missing Tr6bner et al 1992). …”