Optimizes Transformation Rates by Creating Transgenic Roots via Hairy-Root Induction Using Leaf Explants and Optimized Half-Strength Media
This Rhizobium rhizogenes-mediated blueberry transformation protocol optimizes crop transformation by creating transgenic roots via hairy-root induction with leaf explants and an optimized half-strength Woody Plant Medium (WPM). Plant transformation is an essential tool in breeding, enabling gene function validation, trait enhancement, and more recently, supporting the development of new cultivars through genome editing. However, transformation efficiency remains a major bottleneck limiting its practical application. Common transformation methods in blueberry include Agrobacterium-mediated transformation and PEG-mediated transformation using protoplasts. Yet conventional transformation methods in blueberry remain limited because they are often genotype-dependent, labor-intensive, and relatively inefficient. Traditional blueberry transformation systems report efficiencies in the range of roughly 3.7% to 15.3%, limiting the speed and practicality of functional genomics work. Therefore, there is a clear need for a rapid, reliable alternative to accelerate functional genomics and genome editing efforts in blueberry.
Researchers at the University of Florida have developed an enhanced transformation protocol using Rhizobium rhizogenes as a biological delivery system in blueberry. By leveraging hairy root induction, this method creates transformed plant material more rapidly and with higher efficiency than traditional approaches.
Application
This Rhizobium rhizogenes-mediate protocol offers gene function validation, reporter construct testing, early trait screening, and future genome editing workflows in blueberry
Advantages
- Achieves up to 46.7% transformation efficiency, surpassing rates commonly associated with conventional blueberry transformation systems by a large margin
- Detects transgenic roots within 16 days post-infection, enabling quicker construct validation and trait assessment
- Uses half-strength Woody Plant Medium (WPM), lowering media costs while maintaining strong explant growth
Technology
The enhanced standardized protocol for blueberry transformation uses Rhizobium rhizogenes as a delivery system for genetic material. In the process, leaf and stem explants from in vitro-grown blueberry plants are excised, wounded, infected with engineered R. rhizogenes strains carrying a RUBY reporter construct, and transferred through co-cultivation and recovery media under optimized conditions.
The protocol was initially evaluated by comparing two bacterial strains, K599 and Ar. A4, alongside two wounding approaches and two media strengths. The results identified a particularly effective combination using the Ar. A4 strain with leaf explants on half-strength WPM medium. Under these conditions, the system induces hairy roots within 16 days and achieves up to 46.7% transformation efficiency, allowing visual tracking through RUBY-associated red pigmentation. UF researchers further optimized the system by testing six R. rhizogenes strains under multiple antibiotic treatments and different genetic backgrounds. Across treatments, Ar. A4 and ATCC15834 consistently showed the highest transformation efficiencies, reaching up to 80% in one of the selected cultivars.
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