Development of a genetic transformation system for distylous Turnera joelii (Passifloraceae) and characterization of a self-compatible mutant

Abstract

Plants in the genus Turnera provide a useful system for investigating the molecular genetics of distyly and candidate genes involved in this plant breeding system have been proposed. We develop the first transformation system for the genus, using leaf explant tissue of Turnera joelii transformed using Agrobacterium tumefaciens harbouring the pGreen plasmid. Transgenic plants were successfully regenerated using a two growth-medium method and hygromycin resistance as the selectable marker. This should provide a system for testing the function of candidate genes for distyly. We obtained 19 transgenic plants and explore some of their characteristics. We find at least two instances where chromosomal abnormalities have occurred during the transformation process and observe reduced pollen fertility for seven of the transformants, likely evidence for somaclonal variation. We show that the transgenes inserted into two transgenic plants exhibit expected single gene segregation ratios, but find aberrant ratios for a third transgenic plant. The latter plant exhibits a mutant self-compatible phenotype, where self-compatibility is due to a defect in the incompatibility of its pollen. In crosses, the self-compatible transgenic plant shows marked departures from expected single locus ratios at the S-locus determining distyly, with an almost complete lack of transmission of the dominant S-allele. The plant appears to contain more than one copy of the inserted transgene based upon segregation ratios.