Establishment of Agrobacterium-Mediated Transformation System in Sweet Potato (Ipomoea batatas) by Culture of Leaf Segments for Functional Analysis of ASG-1, an Apomixis-Specific Gene

Aims: In order to do the functional analysis of apomixis-specific gene (ASG-1), which was isolated from apomictic guineagrass, the sweet potato was used to establish an Agrobacterium-mediated transformation system.

Study Design: At first, plant regeneration was achieved from the culture of leaf segments of sweet potato. Based on it, a binary vector pSMA35H2-NG for transformation of ASG-1 was used for establishment of a suitable procedure for plant regeneration of transformants.

Place and Duration of Study: Faculty of Environmental and Horticultural Science, Minami Kyushu University, between June 2009 and December 2012.

Methodology: The leaf segments were used for somatic embryogenesis and plantlets regeneration. For the preliminary transformation, a GUS gene set in pSMA35H2-NG was introduced into the Agrobacterium strain GV3101/PMP9, and the Agrobacterium was used to infect the callus derived from leaf segments of sweet potato “Miyazakibeni” and the callus derived from seeds of rice “Nipponbare”. For the plasmid construction, the GUS was replaced by ASG-1, named as pSMA35H2/ASG1. The resultant plasmid was mobilized into Agrobacterium strain GV3101/PMP9 for transformation. For detection of ASG-1, DNAs of the transgenic plantlets were used for PCR, using the primers designed according to ASG-1 and hygromycin, respectively.

Results: 1) When the leaf segments were sterilized with sodium hypochlorite solution of 0.3% and 0.4% for 15 min, 100% of surviving rates was achieved. And the segments cultured on Murashige and Skoog (1962) gave 100% of callus formation rates. 2) When the calli were placed onto Komamine and Nomura (1998) medium for differentiation, somatic embryogenesis was obtained with white color and grain-like tissue, and plantlets with multiple shoot-like tissues were obtained from the somatic embryo. 3) For the preliminary transformation, the calli showed GUS blue spots gradually on the surface. 4) When the pSMA35H2/ASG1 was used to the transformation of the embryogenic calli, the plantlets were developed through multiple shoots. 5) The specific bands of ASG-1 and hygromycin were observed from the PCR products of the plantlets’ DNAs, respectively.

Conclusion: Overall the above results, the procedure using the binary vector pSMA35H2/ASG1 containing ASG-1 revealed, as the first case, that Agrobacterium-mediated transformation system in sweet potato was established using the culture of leaf segments in this study.