An Effective Agrobacterium-Mediated Transient Transformation System for Studying the Lead-Tolerance Genes in Hydrangea

Soil lead (Pb) contamination is a severe environmental issue. Hydrangea, with high ornamental value, shows strong tolerance to the heavy metal Pb. Discovery of the gene(s) determining Pb resistance has been hindered by the lack of a stabilized and efficient genetic transformation system. Agrobacterium-mediated transient transformation overcomes the drawbacks of stabilized genetic transformation, such as long cycle, low efficiency, and high cost. In this study, an Agrobacterium-mediated method was adopted. The percentage of leaves that turned blue after GUS histochemical staining among the total number of infected leaves was used to represent the transient transformation efficiency. The effects of receptor material growth state (leaf age), Agrobacterium concentration, infection time, acetosyringone (Ace) concentration, negative pressure intensity, and co-culture time on the transient transformation efficiency of Hydrangea villosa Rehd. were investigated. Consequently, an efficient transient transformation system harboring the GUS reporter gene with a transient transformation efficiency as high as 100% was successfully established. Using this system, we successfully verified the Pb tolerance of HmPAT1, HmPIF1, and HmZAT7, proving the effectiveness of the transient transformation system. This transient transformation technology will help to discover new Pb-tolerant genes, provide new molecular targets for the development of Pb-resistant Hydrangea, and provide a potential phytoremediation strategy for the treatment of heavy metal pollution in soil.