mPing-Based Transposon Tagging: Soybean Gene Discovery

Development of genomics tools that connect traits to specific genes will result in benefits for all plant breeders and researchers.  To this end, a relatively new mutagenesis system based on the mPing transposon from rice is being deployed in Glycine max.   The mPing element is a relatively small (430bp) DNA transposon and is mobilized by the transposase proteins encoded by the Ping or closely related Pong elements.  Transforming mPing and the Ping transposase genes into soybean produced lines that exhibit active mPing transposition.  Characterization of the heritable mPing insertions produced by these lines indicated that mPing transposed to unlinked sites and preferentially inserted into euchromatin, with over 70% landing in or near (<2.5kb) annotated genes.  Large numbers of these plants are being screened for mutant phenotypes and bulked seeds from these lines are available for distribution. High-throughput methods for insertion site determination are also being developed to facilitate analysis of mPing mutagenized plants.  

Now that that the potential of the mPing-based tagging system has been established, the focus is to increase its effectiveness.  In order to increase the overall transposition rate, new lines expressing modified Pong transposase genes that show higher transposition frequency in a yeast transposition assay are being produced and screened.  Tissue culture treatment is also being tested as a method to increase the transposition rate.  In addition to these strategies, mPing-based activation tags designed to induce overexpression of nearby genes are being developed.  A number of activation tagging constructs have been made and tested in yeast to determine how modification of mPing affects its mobility.  These constructs are currently being tested in soybean and should significantly improve the mutation rate.