INFLUENCE OF AN ARABIDOPSIS DOMINANT NEGATIVE ATHB2 MUTANT ON TOMATO PLANT DEVELOPMENT

R. Iannacone, F. Mittempergher, G. Morelli, G. Panio, A. Perito, I. Ruberti, G. Sessa, F. Cellini
Plants growing in close proximity exhibit the shade avoidance syndrome in response to reflected far-red (FR) radiation from neighbors. The shade avoidance response essentially redirects resources and growth potential from the leaf and storage organs into increased extension growth to optimize light capture by plants. Molecular-genetic studies implicated ATHB2, a homeodomain-leucine zipper (HD-Zip) transcription factor, as a major regulator of the shade avoidance response in Arabidopsis. To further characterize the function of ATHB2 and related HD-Zip proteins (HD-ZIP II), Arabidopsis transgenic plants expressing a derivative of ATHB2 containing a single amino acid substitution in the HD domain (ATHB2N51A), which is known to abolish DNA binding of homodimeric as well as heterodimeric complexes, were generated. This mutation is expected to produce a dominant-negative phenotype. Indeed, at the seedling stage, the phenotype of the ATHB2N51A lines is the same as that shown by antisense ATHB2 lines, but more severe. At later stages of development, the dominant-negative plants produce more leaves and a higher number of lateral inflorescences than the controls. Furthermore, expression of ATHB2N51A in Arabidopsis seedlings attenuates the elongation response induced by shade. We then took advantage of the Arabidopsis dominant negative athb2 mutant to investigate the function of the tomato orthologues. The HD-Zip domain within the HD-ZIP II family has been highly conserved during evolution, and thus it is likely that overexpression of the Arabidopsis ATHB2N51A gene in tomato may result in the formation of heterodimeric complexes with the endogenous HD-ZIP II proteins preventing that of functional dimers. Transgenic tomato expressing constitutively the Arabidopsis ATHB2N51A gene showed strong alteration of the phenotype. Plants had shorter internodes and high proliferation of lateral branches. Furthermore flowering was delayed. We can speculate that the Arabidopsis ATHB2N51A forms heterodimers with the tomato ortholog, so that the transcription of the target gene is highly affected.
Iannacone, R., Mittempergher, F., Morelli, G., Panio, G., Perito, A., Ruberti, I., Sessa, G. and Cellini, F. (2008). INFLUENCE OF AN ARABIDOPSIS DOMINANT NEGATIVE ATHB2 MUTANT ON TOMATO PLANT DEVELOPMENT. Acta Hortic. 789, 263-276
DOI: 10.17660/ActaHortic.2008.789.36
https://doi.org/10.17660/ActaHortic.2008.789.36
HD-Zip proteins, light quality changes, plant architecture, shade avoidance response
English

Acta Horticulturae