Heterologous overexpression of the birch FRUITFULL-like MADS-box gene BpMADS4 prevents normal senescence and winter dormancy in Populus tremula L.
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MADS-box genes have been shown to be important to flower and vegetative tissue development, senescence and winter dormancy in many plant species. Heterologous overexpression of known MADS-box genes has also been used for unravelling gene regulation mechanisms in forest tree species. The constitutive expression of the BpMADS4 gene from birch in poplar, known to induce early flowering in birch and apple, induced broad changes in senescence and winter dormancy but no early flowering. Other analyses revealed that 35S::BpMADS4 poplars maintained photosynthetic activity, chlorophyll and proteins in leaves under winter conditions. BpMADS4 may be influencing transcription factors regulating the senescence and dormancy process due to homology with poplar proteins related to both traits. Little is known of the regulatory genes that co-ordinate senescence, dormancy, chlorophyll/protein degradation, and photosynthesis at the molecular level. Dissecting the molecular characteristics of senescence regulation will probably involve the understanding of multiple and novel regulatory pathways. The results presented here open new horizons for the identification of regulatory mechanisms related to dormancy and senescence in poplar and other temperate tree species. They confirm recent reports of common signalling intermediates between flowering time and growth cessation in trees (Böhlenius et al. in Science 312:1040–1043, 2006) and additionally indicate similar connections between flowering time signals and senescence.
KeywordsChlorophyll Dormancy Homeotic gene MADS-box Photosynthesis Poplar Senescence Transgenic trees
Ribulose-bisphosphate carboxylase large subunit
Optimum quantum yield of photosystem II
Electron transport rate
This study was supported by the Federal Ministry for Research and Education (BMBF). We would like to thank Tuomas Sopanen (University of Joensuu, Finland) for providing the binary vector pAKE1, our co-workers in the Institute of Forest Genetics and Forest Tree Breeding (D. Boedecker, D. Ebbinghaus, E. Moek, A. Pusch, A. Schellhorn, L. Schindler, S. Stern, J. Struss, M. Wellern) for their valuable support, two anonymous reviewers for their very helpful comments during reviewing process, and Dr. Trevor Fenning for language correction as well as other comments.
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