Engineering Agrobacterium for improved plant transformation.

Outside of a few model systems and selected taxa, the insertion of transgenes and regeneration of modified plants are difficult or impossible. This is a major bottleneck both for biotechnology and scientific research with many important species. Agrobacterium-mediated transformation (AMT) remains the most common approach to insert DNA into plant cells, and is also an important means to stimulate regeneration of organized tissues. However, the strains and transformation methods available today have been largely unchanged since the 1990s. New sources of Agrobacterium germplasm and associated genomic information are available for hundreds of wild strains in public repositories, providing new opportunities for research. Many of these strains contain novel gene variants or arrangements of genes in their T-DNA, potentially providing new tools for strain enhancement. There are also several new techniques for Agrobacterium modification, including base editing, CRISPR-associated transposases, and tailored recombineering, that make the process of domesticating wild strains more precise and efficient. We review the novel germplasm, genomic resources, and new methods available, which together should lead to a renaissance in Agrobacterium research and the generation of many new domesticated strains capable of promoting plant transformation and/or regeneration in diverse plant species.