ibclogo XVI International Botanical Congess


Abstract Number: 5445
Session = 15.13.1


HOW THE LAND PLANTS LEARNED THE FLORAL ABC.


G.Theissen, A. Becker, W. Faigl, D. Gassen, K. Henschel, C. Kirchner, B. Meyer, T. Münster, C. Weiser, K. Winter and H. Saedler, MPIZ, Cologne, Germany


Three classes of homeotic functions, termed A, B and C, sculpt thestructure of higher eudicotyledonous flowers, with A specifying sepals, A+B petals, B+C stamens, and C carpels. Most genes providing these functions belong to the MADS-box gene family. To better understand flower origin, we are characterising MADS-box genes of gymnosperms, ferns and mosses. Our analyses suggest that the last common ancestor of ferns and seed plants had homologs, but not orthologs of floral homeotic genes. In contrast, the last common ancestor of extant seed plants had already orthologs of B and C class genes. Expression of C class genes may have distinguished betweenreproductive organs (where expression is on) and non-reproductive organs. B class gene expression could have distinguished between male reproductive organs (expression on) and female ones. Differential expression of B class genes may thus represent the primary sex-determination mechanism of all seed plants.


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