Highly efficient callus-mediated genetic transformation of Parthenium argentatum Gray, an alternate source of latex and rubber

•Direct Agrobacterium-mediated transformation of guayule callus tissues was achieved.•A transformation efficiency of 48 ± 6.5% was obtained in recalcitrant guayule.•The new method is fast and free of unhealthy tissue browning.•The new method should expedite the genetic improvement of guayule.

Transformation efficiency and regeneration of Parthenium argentatum Gray (guayule) from leaf discs is problematical due to genotype-specific regeneration efficiency, browning and tissue culture growth response after Agrobacterium infection of leaf explants. To address this issue, we have developed a callus transformation system using lustrous green nodular callus, termed highly regenerating callus (HRC), which is immensely prolific at shoot regeneration. Agrobacterium tumefaciens strain EHA105 harboring the binary vector pCAMBIA2300 was used to transform the HRC. Primary transformation events and transgenic plants recovered were identified by PCR. Transgene integration and translation of nptII into transgenic plants was confirmed with Southern and western blot analysis. The plant transformation frequency from callus tissues was about 48%. This alternative method is fast and free of undesirable browning and it should facilitate a rapid improvement of guayule germplasm via genetic engineering, which has been slow compared to some other industrial crops.