Molecular genetics of flower development in Arabidopsis thaliana

Citation

Bowman, John L. (1991) Molecular genetics of flower development in Arabidopsis thaliana. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/VJCE-Z966. https://resolver.caltech.edu/CaltechETD:etd-06212007-131544

Abstract

Flowers of Arabidopsis thaliana consist of a precise pattern of organs arranged in four concentric whorls, with each whorl containing a different type of floral organ in characteristic positions and numbers. Arabidopsis flowers begin their development as small outgrowths of cells on the flank of the inflorescence meristem. Cells within each flower primordium must somehow assess their position relative to others and subsequently differentiate accordingly. Homeotic mutations at four loci (AGAMOUS, APETALA2, APETALA3, PISTILLATA) identified in Arabidopsis appear to cause cells in two adjacent whorls of the developing flower primordium to misinterpret their position and differentiate inappropriately. The development of wild-type flowers and that of several alleles of each locus is analyzed as well as the development of double and triple mutant combinations between the homeotic mutations. Based on this genetic data, a model is proposed for how this limited number of floral homeotic genes, by being expressed in overlapping fields of cells in the meristem of the developing flower primordium, and acting alone and in combination, could specify the identity of each of the whorls. AGAMOUS and APETALA2 are proposed to negatively regulate each other's activity with the result that they are expressed in mutually exclusive domains, APETALA2 in the outer two whorls of the flower and AGAMOUS in the inner two whorls. The activities of APETALA3 and PISTILLATA are proposed to be localized to the second and third whorls, with another gene, SUPERMAN, negatively regulating their activities in the fourth whorl. By protein sequence homology to known transcriptions factors, SRF of humans and MCM1 of yeast, AGAMOUS encodes a putative transcription factor. In support of the proposed model, RNA tissue in situ hybridizations to developing flowers show that AGAMOUS RNA is spatially localized to the inner two whorls in developing floral buds. Furthermore, in apetala2 mutant flowers, AGAMOUS RNA is detected in all floral whorls suggesting that APETALA2 negatively regulates AGAMOUS expression in the outer two whorls at the trancriptional level. Expression patterns of AGAMOUS late during flower development suggest that AGAMOUS may also play a role in cell fate specification during cellular differentiation of stamens and carpels.

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