Rapid and efficient production of transgenic bermudagrass and creeping bentgrass bypassing the callus formation phase

Callus culture has been an inevitable step in genetic transformation of monocotyledonous (monocot) species. The induction and maintenance of embryogenic calluses is time-consuming, laborious and also requires experience. A straightforward and callus-free transformation procedure was developed and demonstrated for two monocot species, bermudagrass (Cynodon spp.) and creeping bentgrass (Agrostis stolonifera). Stolon nodes were infected and co-cultivated with Agrobacterium tumefaciens harboring pCAMBIA or pTOK233 binary vectors. Green shoots were directly produced from infected stolon nodes 4-5 weeks after hygromycin selection. Without callus formation and with minimum tissue culture, this procedure allowed us to obtain well-rooted transgenic plantlets in only 7 weeks and greenhouse-grown plants in only 9 weeks. The established plants were screened by PCR; the transgenic nature of the plants was demonstrated by Southern hybridisation analysis. Expression of the transgenes was confirmed by northern hybridisation analysis and GUS staining. Based on the number of transgenic plants obtained and the number of stolon nodes inoculated, transformation frequencies of 4.8%-6.1% and 6.3%-11.3% were achieved for bermudagrass and creeping bentgrass, respectively. The rapid and efficient production of transgenic plants without callus induction is a significant improvement for genetic transformation of monocot species.