Altered expression of flowering class B and class C genes in the Appendix tobacco mutant |
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Authors: | Anne Schoendorf Roberte Bronner Jean Broadhvest François Bernier |
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Institution: | (1) I.B.M.P. du C.N.R.S., Institut de Botanique, 28 rue Goethe, 67083 Strasbourg Cedex, France Tel. +33-3-88358270; Fax +33-3-88358484 e-mail: Francois.Bernier@ibmp-ulp.u-strasbg.fr, FR |
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Abstract: | In the tobacco (Nicotiana tabacum) Appendix mutant, anthers are tipped by a miniature style and stigma. The outgrowth appears on the anther when it is already
differentiating and follows the developmental timing of the central carpel. The Appendix mutation thus represents a late homeotic
transformation suggesting that the APPENDIX (APX) gene either could be a misregulated organ identity gene or could be involved in regulating the expression of such genes.
RFLP analysis with two class B (TM6 and NTGLO) and a class C (NAG) probes revealed that the Appendix phenotype is not caused by a mutation in one of these genes. However, in situ hybridization
showed important changes in the expression of NTGLO and NAG in the mutant when compared with wild-type tobacco. Surprisingly, although no phenotypic alteration other than the style
and stigma outgrowth is observed in the Appendix mutant, changes in class B and class C gene expession were not restricted
to the anther tip cells from which the outgrowth originates. As expected, NAG was expressed in the Appendix outgrowth but it was also overexpressed in the normal third and fourth whorl organs at the
time the outgrowth, as well as the central styles and stigmas, differentiated. Overexpression of a class C gene is probably
responsible for the Appendix phenotype. In normal and mutant flowers, NTGLO was expressed in the second, third and fourth whorls up to the time of carpel fusion. Expression of this class B gene then
ceased in the fourth whorl organs but was reactivated at later stages only in the styles and stigmas as well as in the outgrowths
of the mutant. It thus seems that the function of the APX gene is either to regulate the late expression of organ identity genes or to control cell proliferation in such a way that,
in the mutant, some cells are in a state where they respond in an unusual way to developmental signals.
Received: 17 October 1997 / Revision accepted: 24 March 1998 |
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Keywords: | Nicotiana tabacum Flowering Mutant Carpelloidy Development |
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