Rapid genetic transformation of herbaceous peony without tissue culture via Agrobacterium rhizogenes: Optimization using rhizomes, stems, roots, and seedlings.

Herbaceous peony is a famous traditional flower worldwide. However, the lack of a robust transgenic system has severely restricted its genetic improvement efforts. In this study, we established a tissue culture-free Agrobacterium rhizogenes-mediated transformation system using the rhizomes, stems, root segments, and seedlings of herbaceous peony. Soaking rhizomes and root segments in a resuspension solution containing acetosyringone and 2-morpholinoethanesulfonic acid induced more GFP-positive hairy roots than that in other tissues. Our study also revealed that colony smear was the optimal infection method for stems and seedlings, that one-year-old seedlings were most susceptible to infection, and that Agrobacterium strain K599 was more effective than MSU440 and C58C1. Among the 11 cultivars, even though all formed hairy roots, 'Dafugui' of the Lactiflora group showed the highest transgenic efficiency. This study provides a rapid and efficient tissue culture-free strategy for the genetic transformation of herbaceous peony, providing an important basis for its molecular breeding.