MEC BFU 2005-01031, 2005-2008

Principal Investigator: José Luis Micol.
Investigators: Raquel Sarmiento Mañús, Almudena Mollá Morales, Almudena Ferrández Ayela, David Esteve Bruna, Rubén Casanova Sáez, Héctor Candela Antón and Sara Jover Gil.
Instituto de Bioingeniería. Universidad Miguel Hernández.

Molecular nature, action and interactions of some Arabidopsis thaliana genes required for leaf venation pattern formation

We already gathered a large collection of Arabidopsis thaliana mutants, which presented perturbations in the architecture of their vegetative leaves and were therefore considered potentially useful for identifying genes required for leaf organogenesis. A number of our mutants will be used in this project in order to determine the molecular nature, action and interactions of several genes required for two developmental aspects of the making of a leaf: leaf venation pattern formation and the differential contribution of the epidermis and the internal leaf tissues to leaf development.

The venation patterns of insect wings and plant leaves can be considered two-dimensional and provide simple models for dissecting the cellular and molecular processes responsible for the generation of tree-like branched biological structures, such as the vascular systems of animal and plant species. We propose here the genetic and molecular characterization of two mutants with slightly perturbed leaf morphology but strongly perturbed venation pattern that we isolated and named apiculata7 (api7) and rotunda1 (ron1).

We identified in addition mutants whose leaf vascular network can be clearly distinguished as a green reticulation on a paler lamina. We named these mutants venosa (ven), some of which (ven2) were found to carry alleles of the RETICULATA (RE) gene, a classical genetic marker. Contrary to many other leaf mutants studied in Arabidopsis thaliana, we observed very little pleiotropy in the ven lines, whose only obvious aberration at first sight is the reticulation exhibited by cotyledons and leaves. Our preliminary results indicate that the leaves of re mutants are of almost normal shape in spite of their extremely reduced mesophyll cell density, which suggests that the epidermis plays a major role in regulating leaf shape in Arabidopsis thaliana, whereas the correct development of the mesophyll tissue is more important in the control of leaf thickness. We propose here to test such a hypothesis by means of the genetic and molecular characterization of mutants displaying phenotypes similar to that of re (ven1, ven3 and ven4) or carrying mutations in genes with homology to RE (re2).