Establishment of an efficient Agrobacterium-mediated genetic transformation protocol for Saccharum officinarum using Black Cheribon as a model genotype

Abstract

Efficient Agrobacterium-mediated transformation (AMT) is vital for the biotechnological improvement of sugarcane (Saccharum spp.). Saccharum officinarum is the main ancestor of all modern cultivars, yet little research has been conducted on its AMT system. In this work, an efficient AMT protocol for S. officinarum was developed, with Black Cheribon as the model genotype owing to its superior tissue culture performance and regeneration capacity. The optimized agro-infection protocol comprised the following main parameters: concentration of acetosyringone (AS) in Agrobacterium culture, concentration of AS for infection, Agrobacterium concentration at OD600 = 0.4, infection time of 30 minutes, vacuum infiltration time of 10 minutes and co-cultivation time of 3 days. To further improve transformation efficiency, 0.5 mg/L thidiazuron and 200 mg/L citric acid were added to the regeneration medium, which enhanced the regeneration of shoots. A modified stage-dependent selection strategy (FlexII) was established by using glufosinate-ammonium at concentrations of 2.0, 1.0, and 0.75 mg/L in the callus proliferation, shoot regeneration, and rooting stages, respectively. This strategy was more successful than the minimum inhibitory concentration-based strategy in S. officinarum transformation. The optimized protocol further boosted the transformation efficiency of Black Cheribon from 1.12% to 7.17%. The resulting transgenic lines were confirmed by PCR amplification of T-DNA regions and immunochromatographic detection of Bar protein expression in primary transformants, respectively. These results provide a sound technical foundation for the functional genomics and biotechnological optimization of S. officinarum germplasm, and may serve as a reference for future transformation studies in other sugarcane germplasm.