Chimaeras and Transgenic Plant Mosaics: A New Tool in Plant Biology

Abstract

Chimaeras are genetic mosaics composed of intermixed genetically different tissues. Transposable elements can be used to activate gene expression in clonal populations of cells and consequently to generate genetic mosaics. To achieve this a gene of interest (e.g. morphogenetic genes from plant pathogens) is split by a transposable element in such a way that excision events will reactivate gene expression in transgenic plants. Excision events taking place late during plant organ development will generate extra-apical mosaics composed of intermixed tissues with wild-type and mutant phenotype. In particular, the use of a transposon-split 35sipt gene to raise plants transgenic for a cytokinin synthetising gene, whose constitutive expression is not compatible with plant regeneration is presented. Moreover we have constructed a chimaeric gene composed of the 35s RNA promoter of cauliflower mosaic virus and the indoleacetic-acid lysine synthetase of Pseudomonas savastanoi and defined the morphological alterations established by iaal gene expression in transgenic plants.