Application of uniconazole in improving the high-throughput genetic transformation efficiency in maize

Agrobacterium-mediated genetic transformation is the most effective and widely used delivery system for candidate genes and genome editors in maize, which is an important crop with the largest planting area and the highest yield. Here, we used gibberellin synthesis inhibitor, uniconazole, to enhance the stem strength of regenerated plantlets resulting in a significantly increase from 11.6 % to 18.2 % in the percentage of regenerated plantlets, and the transformation frequency was also improved from 9.4 % to 15.6 % in the test experiments. The physiological condition of immature embryo is greatly affected by ear source, season and insect pests, while it can cause significant fluctuations in the transformation frequency. Our optimization works at the differentiation subculture stage, avoiding the impact on the physiological condition of immature embryo. So, it can be applicated to high-throughput genetic transformation in different seasons and different ear sources throughout the year. The productive experiment results indicated that the annual average transformation frequency significantly improved from 2.76 % to 7.14 % (approximately 2.6 folds improvement), and the tissue culture cycle was shortened from 115 days to 106 days by using optimized system. Our optimized genetic transformation system opens avenues for maize improvement based on transgenic and genome editing technology.