Overexpression of PeBBM2 and PeWUS Genes via Carbon Nanotube-Based DNA Delivery Enhances the Callus and Shoot Formation in Phyllostachys edulis

Background/Objectives: Phyllostachys edulis is the most widely distributed and economically important bamboo species in China. However, the genetic transformation in P. edulis is still limited by a long regeneration cycle and low regeneration and transformation efficiency. Carbon nanotube-based delivery systems in plants have the advantages of simplicity, rapidity and low cost. Moreover, morphogenetic regulators BBM (BABY BOOM) and WUS (WUSCHEL) play significant roles in plant regeneration. Methods: Here, immature zygotic embryos were used to induce P. edulis callus, and using single-walled carbon nanotubes (SWNTs)-based delivery technology, PeBBM2, PeWUS-DNA (with introns) and PeWUS-cDNA (without introns) were introduced to P. edulis callus either individually or in combination. Conclusions: The results showed that the 0.9–1.0 mm (long axis) embryos exhibited the lowest contamination rate and the highest induction efficiency. Moreover, the results indicated that the co-transformation of PeBBM2-PeWUS more effectively boosted the growth area of the callus. However, only the PeBBM2-overexpression callus could form shoots. Compared with the wild type, the PeBBM2-overexpression lines showed reduced expression of AGL15 and increased expression of IAA30 and YUC. In conclusion, these findings suggested that SWNTs-mediated DNA delivery is a potential strategy for the genetic transformation of P. edulis callus. Additionally, the findings indicate‌ that the PeBBM2 and PeWUS genes can accelerate callus enlargement in P. edulis, whereas PeBBM2 might play a more important role in shoot formation. This study provides a basis for developing a genetic transformation system for plants based on SWNTs-mediated DNA delivery and morphogenetic regulators.