Agrobacterium-mediated Transformation of Zoysiagrass [Zoysia matrella (L.) Merr.] Using Embryogenic Callus versus Shoot Cultures.

Genetically improved zoysiagrass cultivars have been developed and released for quite some time using traditional breeding methodology.   The application of plant biotechnological approaches, however, has also proven to be a powerful tool for the enhancement of agronomic traits in numerous crops by incorporating the vast array of genes from different species. There are a few reports describing transformation in the genus (Zoysia japonica Steud. and Z. sinica Hance), though in general the transformation frequency is low. Transformation of Z. matrella (L.) Merr. is far from routine and is genotype dependent. Reported  Agrobacterium-mediated transformation protocols for Zoysia species have used either highly embryogenic callus or stolon nodes.  The present study compares Agrobacterium-mediated transformation efficiency using callus tissue versus shoot cultures with selected cultivars of the recalcitrant Z. matrella species.  We have successfully transformed highly embryogenic callus of the experimental zoysiagrass variety, DALZ 0501, using Agrobacterium-mediated transformation with a hygromycin selectable marker and GUS as a reporter gene.  Our preliminary analysis of transient GUS expression showed a transformation efficiency of 1 - 2 %, which is low when compared to other turfgrasses.  Variables under study to enhance the transformation efficiency include different media components during co-cultivation.  The results from this study will potentially lead us to identify a reliable transformation system and formulate a base protocol for efficiently transforming different cultivars of Z. matrella in a routine fashion.