Overexpression of the VvLTP1 gene interferes with somatic embryo development in grapevine

Grapevine (Vitis vinifera L.) embryos have an early developmental pattern which differs from the one observed in model angiosperms such as Arabidopsis, in that the plane of divisions show variations from one individual to another. Furthermore, the protoderm (the first tissue to differentiate) does not form in one step but rather, gradually with time during globule formation. In Arabidopsis, expression pattern of a particular lipid transfer protein (LTP) isoform, AtLTP1, appears to be related to protoderm establishment, and is considered as a molecular marker of its differentiation. To investigate whether a similar role for LTPs in the development of grapevine embryos, we investigated the expression pattern of VvLTP1, a Vitis homologue of AtLTP1, in somatic embryo development. Expression of the GUS reporter gene under the control of the VvLTP1 promoter demonstrated that this LTP isoform is a marker of protoderm formation, and confirmed that this tissue forms sequentially over time. Ectopic expression of VvLTP1 under the control of the 35S promoter led to grossly misshapen embryos, which failed to acquire bilateral symmetry and displayed an abnormal epidermal layer. These results indicate that a correct spatial or temporal expression, or both, of this gene is essential for grapevine embryo development.