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

Verona, Italy - 24/27 September, 2003

ISBN 88-900622-4-X

Oral Communication Abstract - S4c

PhEXP18, A PETUNIA ALPHA EXPANSIN GENE: SEEKING FOR THE FUNCTION

S. ZENONI*, L. REALE**, G. B. TORNIELLI*, L. LANFALONI***, A. PORCEDDU****, A. FERRARINI*, A. ZAMBONI*, C. MORETTI**, F. FERRANTI**, M. PEZZOTTI*

*) Dipartimento Scientifico e Tecnologico, Università degli Studi di Verona

**) Dipartimento di Biologia Vegetale e Biotecnologie Agroambientali, Università degli Studi di Perugia

***) Dipartimento di Biologia Cellulare e Molecolare, Università degli Studi di Perugia

****) Istituto di Genetica Vegetale- CNR

cell expansion, cellulose, downregulation, expansin, Petunia hybrida

In plants, organ shape is determined by organised and regulated control of cell expansion together with cell division. Emerging data support the view that the direction and magnitude of the enlargement of the primary cell wall largely determine the expansion pattern and thereby the final shape and size of the cells.

Cell wall proteins are believed to play important roles in regulating cell wall extensibility which is a key parameter determining cell expansion. Among cell wall proteins studied to date, expansins are unique in the ability to induce immediate cell wall extension in vitro and cell expansion in vivo. Expansin genes have been identified in many plant species and make up a large superfamily that is divided into two major families, alpha- and beta-expansins, on the basis of the sequence divergence and biochemical activity. During flower development, floral organs typically assume their final shape after mitotic activity has basically ceased, indicating that cell expansion plays an important role in determining organ shape.

To initiate the investigation on the function of expansins in vivo and during plant development, we cloned PhEXP18, a Petunia hybrida alpha-expansin gene, determined its pattern of spatial and temporal expression in plant and flower organs and generated transgenic Petunia lines that express the cDNA encoding PhEXP18 in the antisense orientation under control of the strong and constitutively expressed cauliflower mosaic virus (CaMV) 35S promoter. PhEXP18 was expressed mainly in petals, ovaries and stems. (In petals the expression was higher in the distal portion (limb) in comparison to the basal portion (tube). Transgenic plants with reduced PhEXP18 expression levels showed a strong reduction of petal limb size compared to wild-type. Microscopic observations revealed that antisense line petal limb epidermal cells were smaller and showed a reduction in cell wall thickness when compared to wild-type cells. Further analysis revealed that the reduction in thickness of the antisense line cell walls might be attributed to a deficiency in crystalline cellulose.