Expression of a heterologous expansin in transgenic tomato plants

Expansins are cell wall proteins thought to play an important role in growt h and other events involving cell wall modifications. Whereas the expressio n patterns of many isoforms have been characterised, the nature of their ac tivity is still poorly understood. Large amounts of active expansins are ne cessary to undertake biochemical studies and identify their substrates. We report here the successful expression of a recombinant expansin [CsExp1, is olated from cucumber (Cucumis sativus L.) hypocotyls] in transgenic tomato (Lycopersicon esculentum Mill.) plants, under the control of a constitutive promoter. In some transformants, CsExp1 transcript and protein accumulated to high levels. and expansin activity extractable from the cell walls was increased up to about 20-fold the activity measured in wild-type plants. Th ese results confirm the identity of the CxExp1 coding sequence, and will en able large quantities of active expansin to be obtained for further studies .