Efficient plastid transformation in tobacco using small gold particles (0.07^|^#8211;0.3^|^#8201;^|^micro;m)

Plastid transformation methods have been developed for 20 plant species. However, only a few plant species, such as tobacco and lettuce, have been used in applied studies because transformation efficiencies are extremely low in other species. Plastid transformation has been mainly performed by particle bombardment using 0.6-µm gold particles as microcarriers of the transformation vector. Because the target materials in some plant species are undeveloped proplastids rather than fully developed chloroplasts, optimizing microcarrier size for the target size is a major consideration. In this study, we evaluated the availability of gold particles (0.07, 0.08, 0.1, 0.2, and 0.3 µm) that were smaller than those used for plastid transformation in previous studies. We obtained stable plastid transformants of tobacco with sufficient efficiency using all the tested small gold particles as the same level as 0.6-µm gold particles, even the smallest (0.07 µm). The average number of transformants obtained with 0.3-µm particles (9.3±4.6 per plate) was the highest among the tested gold particles. Because small gold particles were revealed to be sufficient for plastid transformation in a model tobacco plant, it is suggested that choosing appropriate small-sized gold particles which have never been used before will improve plastid transformation in many plant species.