An Efficient System for Agrobacterium-Mediated Transformation of Elite Cultivars in Brassica juncea

Efficient genetic transformation approaches play pivotal roles in both gene function research and crop breeding. However, stable transformation in mustard, particularly for different horticultural types, has not been systematically studied and well-established so far. In this study, we optimized the key factors in the genetic transformation of mustard, including the optical density value of Agrobacterium suspension, the age of explants, and the combination of phytohormones at different concentrations. As a result, the optimal conditions for the genetic transformation of leaf and stem mustard included hypocotyl explants derived from 4-day-old seedlings, infection by 0.8 OD600nm Agrobacterium suspension, and then re-differentiation on a medium containing 4 mg/L trans-zeatin (tZ) and 0.1 mg/L indoleacetic acid (IAA) for leaf mustard, and for stem mustard, re-differentiation on a medium containing 2 mg/L tZ and 0.4 mg/L IAA, with positive rates of 4.74% and 5.26%, respectively. Those for root mustard were hypocotyl explants derived from 8-day-old seedlings, infection by 0.2 OD600nm Agrobacterium suspension, and a medium containing 2 mg/L tZ and 0.1 mg/L IAA, with a positive rate of 4.42%. Overall, this work provides an effective tool for both the theoretical study and genetic improvement of Brassica juncea.