Proceedings of the XLVII Italian Society of Agricultural Genetics - SIGA Annual Congress

Verona, Italy - 24/27 September, 2003

ISBN 88-900622-4-X

Poster Abstract - 4.07

EPiPHyLLY IN THE VARIANT CLONE EMB-2 OF THE INTERSPECIFIC HYBRID HELIANTHUS ANNUUS X H. TUBEROSUS: EXPRESSION OF A KNOTTED1-LIKE HOMEOBOX GENE AND CYTOKININ DISTRIBUTION IN LEAVES

V. MICHELOTTI*, L. BRUNO**, A. CHIAPPETTA**, M. PETRARULO**, M. FAMBRINI*, M. SALVINI*^,****, H. VAN ONCKELEN***, M.B. BITONTI**, C. PUGLIESI*

*) Università di Pisa, Dipartimento di Biologia delle Piante Agrarie - Sezione di Genetica, via Matteotti 1/B, I-56124 Pisa, Italy

**) Università della Calabria, Dipartimento di Ecologia - Laboratorio di Botanica, Cubo 6B, Arcavacata di Rende, I-87030 Cosenza, Italy

***) Department of Biology, University of Antwerp, Belgium

****) Scuola Normale Superiore, Piazza dei Cavalieri, 7 I-56124 Pisa, Italy

homeotic gene, adventitious regeneration, hormone, epiphylly

Structures such as shoots, leaves, embryos and inflorescences may occur upon a leaf or leaf homologue. This phenomenon known as epiphylly is an expression of the morphogenetic potentiality, typical of plant cells (Dickinson, 1978). The flexibility of plant cells has been widely used in vitro tissue cultures which nowadays are considered a support to plant breeding and biotechnology (Jain, 2001). However, the genetic basis of the acquisition of organogenetic and embryogenetic competence are not completely known. It is likely that somatic organogenesis and embryogenesis phenomena in vitro need the same gene regulation hierarchy that control in vivo development of both meristems and zygotic embryos. To verify this hypothesis, an useful plant material are cell lines or mutants that show an high organogenetic and embryogenetic ability without exogenous hormonal requirement (Fambrini et al., 2001).

A somaclonal variant (EMB-2) isolated from in vitro regeneration of the interspecific tetraploid hybrid (2n = 4x = 68) Helianthus annuus x H. tuberosus shows, without hormonal treatments, ectopic formation of epiphyllous shoots and embryos usually arranged in clusters or rows along preexisting veins (Fambrini et al., 2000). This phenotype that is vegetatively propagated resembles some characteristics described in plants with high endogenous cytokinin level or overexpressing Knotted- and/or Leafy Cotyledon-like genes.

Here we report the expression analysis of a Knotted1-like homeobox gene (Knot1HT) and the pattern of cytokinin accumulation in EMB-2 leaves. The results obtained suggested the involvement of the Knot1HT gene in development of epiphyllic structures. Moreover, we observed a strong signal of trans-zeatin in the parenchimatic cells associated with vascular bundles and along epidermal layer where the cells that resume the mitotic activity are determinated to differentiated the epiphyllic structures. The concomitant localization of cytokinins and Knot1HT transcripts in both the parenchymal cells of vascular bundles and ectopic embryos or shoots, suggest a correlation between these factors and the induction of epiphyllic phenomena.

References

Dickinson TA. (1978) Epiphylly in angiosperms. Botanical Rev. 44: 181-232.

Fambrini M., Cionini G., Bianchi R., Pugliesi C. (2000) Epiphylly in a variant of Helianthus annuus x H. tuberosus induced by in vitro tissue culture. Int. J. Plant Sci. 161: 13-22.

Fambrini M., Fisichella M., Pugliesi C. (2001) Enhanced morphogenetic potential from in vitro regenerated plants of genus Helianthus: an overview. Recent Rec. Develop. Plant Biol.1: 35-54.

Jain SM. (2001) Tissue culture-derived variation in crop improvment. Euphytica 118: 153-166.