Genetic and morphological analysis of floral homeotic mutants tepal-like bract and fagopyrum apetala of Fagopyrum esculentum Maria D. Logacheva, Ivan N. Fesenko, Aleksey N. Fesenko, and Aleksey A. Penin Abstract: The studies on floral homeotic mutants of the model plant species Arabidopsis thaliana (L.) Heynh. and Anti- rrhinum majus L. have clarified many important aspects of the genetic control of flower development. However, the de- tails of this process can vary in species representing different lineages of flowering plants. The studies on floral homeotic mutants of nonmodel plant species may significantly improve the understanding of the mechanisms of morphological evo- lution of flowers. We report here the results of the genetic and morphological analysis of two floral homeotic mutants of common buckwheat (Fagopyrum esculentum Moench.). The mutant, tepal-like bract (tlb), is characterized by the transfor- mation of bracts into petaloid organs, whereas fagopyrum apetala (fap), has a carpelloid perianth. Both mutant phenotypes are caused by a single recessive nuclear mutation. The double mutant fap tlb combines the features of tlb and fap. Our re- sults show that single gene mutations are sufficient to convert the buckwheat bract into a tepal and to confer carpel iden- tity on first whorl organs. These results are consistent with the premise that variations on the ABC model can be used to explain a wide range of floral architectures. Key words: Fagopyrum, homeotic mutants, homeosis, flower development, ABC model. Re ´sume ´: L’e ´tude de mutants floraux home ´otiques des plantes mode `les Arabidopsis thaliana (L.) Heynh. et Anthirrhinium majus L. ont clarifie ´ plusieurs aspects du contro ˆle ge ´ne ´tique du de ´veloppement floral. Cependant, les de ´tails de ce proces- sus peuvent varier selon les espe `ces repre ´sentant diffe ´rentes ligne ´es de plantes a ` fleurs. Les e ´tudes sur les mutants floraux home ´otiques portant sur des espe `ces de plantes non-mode `les peuvent ame ´liorer significativement la compre ´hension des me ´canismes de l’e ´volution morphologique des fleurs. Les auteurs rapportent les re ´sultats de l’analyse morphologique et ge ´- ne ´tique de deux mutants floraux home ´otiques du sarrasin (Fagopyrum esculentum Moench.). Le mutant, bracte ´es te ´paloı ¨- des (tlb), se caracte ´rise par la transformation des bracte ´es en organes pe ´taloı ¨des, alors que le fagopyrum apetala (fap) posse `de un pe ´rianthe carpelloı ¨de. Ces deux phe ´notypes mutants sont cause ´s par une mutation nucle ´ique re ´cessive unique. Le double mutant fap tlb combine les caracte ´ristiques des tlb et des fap. Les re ´sultats montrent que des mutations a ` ge `ne unique suffisent pour convertir la bracte ´e du sarrasin en te ´pale et a ` confe ´rer une identite ´ de carpelle au premier verticille d’organes. Ces re ´sultats concordent avec la pre ´misse que les variations sur le mode `le ABC peuvent e ˆtre utilise ´es pour ex- pliquer un ensemble d’architectures florales. Mots-cle ´s : Fagopyrum, mutant home ´otique, home ´osis, de ´veloppement floral, mode `le ABC. [Traduit par la Re ´daction] Introduction Recent advances in plant developmental genetics, phylo- genetics, and genomics have increased the understanding of many important aspects of flower development. The model of the genetic control of floral organ identity has been pro- posed by Coen and Meyerowitz (1991). This model has been inferred from the studies on floral homeotic mutants of the model plants, Arabidopsis thaliana (L.) Heynh. and Anti- rrhinum majus L. Their flowers, as well as most eudicot flowers, consist of four classes of organs arranged in four whorls: sepals, petals, stamens, and carpels (Fig. 1a). Muta- tions in a single gene can cause the transformation of one type of floral organ into another. In Arabidopsis, mutation in the APETALA2 (AP2) gene results in carpelloid first- whorl structures instead of sepals, in APETALA3 (AP3) and PISTILLATA (PI) second whorl organs have the identity of sepals and third whorl organs are carpelloid, respectively. Mutation in the AGAMOUS (AG) gene results in the lack of reproductive organs (stamens and carpels); these are trans- formed into petals and sepals, respectively. This mutation is also characterized by an indeterminate floral meristem (Bowman et al. 1989). The existence of these classes of mu- tants suggests that development of the flower is controlled by three classes of genes referred to as A, B, and C (Haughn and Somerville 1988; Coen and Meyerowitz 1991; Weigel and Meyerowitz 1994). The expression of A-class genes Received 30 July 2007. Published on the NRC Research Press Web site at botany.nrc.ca on 3 April 2008. M.D. Logacheva. 1 Faculty of Bioengineering and Bioinformatics, M.V. Lomonosov Moscow State University, Vorobyevy Gory 1-73, Moscow 119991, Russia. I.N. Fesenko and A.N. Fesenko. All Russia Scientific Research Institute of Legumes and Groat Crops, pos. Streletskoe, 302502, Orel, Russia. A.A. Penin. Department of Genetics, Biological Faculty, M.V. Lomonosov Moscow State University, Vorobyevy Gory 1-12, Moscow 119991, Russia. 1 Corresponding author (e-mail: maria.log@gmail.com). 367 Botany 86: 367–375 (2008) doi:10.1139/B08-010 # 2008 NRC Canada