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In an article,” Beyond the ABCs” ternary complex formation in the control of floral organ identity, in the November, 2000 issue of Trends in Plant Science, Drs. Marcos Egea Gutierrez-Cortines at the Universidad of Cartagena, Spain and Brendan Davies at the Leeds Institute for Plant Biotechnology and Agriculture review current progress in the floral organ identity and suggest the future direction of research in this field involving the role of MADS-box and ternary complex formation.
The authors begin the review by explaining the classical model of floral development. According to this model, the identities of the floral organs within the four whorls, namely sepals, petals, stamens and carpels are conditioned by the combinatorial action of three genetic functions, designated A, B and C. Floral expression of the A function directs sepal formation. Petals are formed as a result of combined functions of Aand B. The expression of B and C together leads to stamen development. and the expression of C alone results in the formation of carpels.. Recent studies have shown that the A,B and C are not the only MADS-box factors that determine the identity of floral organs. Cosuppression of the petunia FBP2 MADS-box gene and antisense downregulation of the related tomato TM5 MADS-box gene, resulted in a loss of floral organ identity and determinacy. The data obtained from these, and other experiments demonstrate that the class of MADS-box genes, called “Im genes”, as exemplified by FBP2 and TM5, play a role in determining floral organ identity.
This role is supported by yeast two- and three-hybrid analyses of the interactions of A, B C and Im MADS-box factors. Recent experiments have shown that when all members of the Im-class of MADS-box genes are inactivated in Arabidopsis, the triple mutant plants produce indeterminate flowers lacking petal, stamen and carpel identity. The authors suggest that this class of MADS-box genes are essential for the activity of the B and C factors and that they act by forming heteromultimers with the ABC organ identity factors. There is evidence that the hetero- multimerisation of these factors might influence their ability to activate the transcription of target genes.
In conclusion, the authors view the field of floral organ identity as an area in which there is still much to learn. According to them, future studies need to address the mechanisms of heteromultimerization and DNA-binding, and the roles they play in the regulation of target gene expression.
In conclusion, the authors view the field of floral organ identity as an area in which there is still much to learn particularly about the MADS-box factors which influence floral organ formation. According to them, future studies need to address the mechanisms of heteromultimerization and DNA binding, and the roles they play in the regulation of target gene expression.