Transformation of `Bosc' Pear (Pyrus communis L.) with the rolC Gene from Agrobacterium rhizogenes and Characterization of Transgenic Plants
Pear production in the United States relies on a few major cultivars, including `Bosc'. While there is a need for new cultivars, genetic improvement of the existing major cultivars through genetic transformation could have a major impact on the industry. We have developed a system for regeneration and transformation of pear. While the major objective of the transformation project is to improve resistance to fire blight (Erwinia amylovora) in major pear cultivars, tree size control is also one of the objectives in the genetic improvement of pear that may be approached through transformation. Traditionally, manipulation of tree size and vigor in established cultivars has been achieved through the use of size-controlling rootstocks. There are no completely satisfactory size-controlling rootstocks for pear. Genetic transformation provides an approach to developing new size-controlling rootstocks and also to directly affect the growth of the transgenic scion cultivar using genes that affect plant growth such as the rolC gene isolated from the bacterium A. rhizogenes, the causal agent of “hairy root” disease. This gene has been shown to alter growth and development in a number of plant species. To investigate the potential utility of the rolC gene in altering the growth of pear trees, `Bosc' pear was transformed with A. tumefaciens EHA101 carrying a pGA482-based plasmid containing the NPTII and GUS genes, and the rolC gene under the control of its native promoter. Four clones were isolated that were kanamycin-resistant and GUS-positive. PCR assays and DNA blots indicated the presence of the rolC gene in these clones. Each transgenic clone has been multiplied in vitro and planted in the greenhouse where transgene expression and plant growth are being evaluated.