Isopentenyl Transferase (IPT) Gene Transfer to Perennial Ryegrass Through Sonication-Assisted Agrobacterium-Mediated Transformation (SAAT), Vacuum and Heat Treatment

Production of transgenic periclinal chimeras in pumpkin - a tool for revealing cell fates of L1 meristem

Genetic engineering is commonly used to improve the agronomic traits of crops. However, genetic transformation in pumpkin remains a challenge. Conducting transformation trials, we accidentally created transgenic L1 periclinal chimeras in pumpkins. Using our modified Agrobacterium-mediated transformation, we generated transgenic L1 periclinal chimeras which have high value in research on development of the meristem. Fluorescence observations of transformed L1 cells enabled us to reveal cell fates. These L1 cells can develop into stomata, epidermal hairs, seed coat, and epidermis of the root, stem, leaf, flower, and fruit. These periclinal chimeras can be propagated vegetatively with minimal risk of transgene flow. This study offers new perspectives on development of the meristem and a promising technique for creating transgenic periclinal chimeras in plants.

Efficient genotype-independent cotton genetic transformation and genome editing

Cotton (Gossypium spp.) is one of the most important fiber crops worldwide. In the last two decades, transgenesis and genome editing have played important roles in cotton improvement. However, genotype dependence is one of the key bottlenecks in generating transgenic and gene-edited cotton plants through either particle bombardment or Agrobacterium-mediated transformation. Here, we developed a shoot apical meristem (SAM) cell-mediated transformation system (SAMT) that allowed the transformation of recalcitrant cotton genotypes including widely grown upland cotton (Gossypium hirsutum), Sea island cotton (Gossypium barbadense), and Asiatic cotton (Gossypium arboreum). Through SAMT, we successfully introduced two foreign genes, GFP and RUBY, into SAM cells of some recalcitrant cotton genotypes. Within 2-3 months, transgenic adventitious shoots generated from the axillary meristem zone could be recovered and grown into whole cotton plants. The GFP fluorescent signal and betalain accumulation could be observed in various tissues in GFP- and RUBY-positive plants, as well as in their progenies, indicating that the transgenes were stably integrated into the genome and transmitted to the next generation. Furthermore, using SAMT, we successfully generated edited cotton plants with inheritable targeted mutagenesis in the GhPGF and GhRCD1 genes through CRISPR/Cas9-mediated genome editing. In summary, the established SAMT transformation system here in this study bypasses the embryogenesis process during tissue culture in a conventional transformation procedure and significantly accelerates the generation of transgenic and gene-edited plants for genetic improvement of recalcitrant cotton varieties.

Callus Induction from Diverse Explants and Genotypes Enables Robust Transformation of Perennial Ryegrass (Lolium perenne L.)

Genetic transformation of perennial ryegrass (Lolium perenne L.) is critical for fundamental and translational research in this important grass species. It often relies on Agrobacterium-mediated transformation of callus tissue. However, callus induction is restricted to a few genotypes that respond well to tissue culture. Here, we report callus induction from different perennial ryegrass genotypes and explants, such as shoot tips, seeds, and anthers, which were transformed with several plasmids for functional genomics. β-glucuronidase (GUS) histochemical staining showed the LmdsRNAbp promoter sequence was active in stigmas, spikelets, anthers, and leaves. We also transformed calli with plasmids allowing gene silencing and gene knock-out using RNA interference and CRISPR/Cas9, respectively, for which genotypic and phenotypic investigations are ongoing. Using 19 different constructs, 262 transgenic events were regenerated. Moreover, the protocol regenerated a doubled haploid transgenic event from anther-derived calli. This work provides a proof-of-concept method for expanding the range of genotypes amenable to transformation, thus, serving research and breeding initiatives to improve this important grass crop for forage and recreation.

Establishment of an efficient Agrobacterium-mediated genetic transformation system in halophyte Puccinellia tenuiflora

Alkaligrass (Puccinellia tenuiflora) is a monocotyledonous halophyte pasture, which has strong tolerance to saline-alkali, drought, and chilling stresses. We have reported a high-quality chromosome-level genome and stress-responsive proteomic results in P. tenuiflora. However, the gene/protein function investigations are still lacking, due to the absent of genetic transformation system in P. tenuiflora. In this study, we established a higher efficient Agrobacterium-mediated transformation for P. tenuiflora using calluses induced from seeds. Agrobacterium strain EHA105 harbors pANIC 6B vectors that contain GUS reporter gene and Hyg gene for screening. Ten mg·L-1 hygromycin was used for selecting transgenic calluses. The optimized condition of vacuum for 10 min, ultrasonication for 10 min, and then vacuum for 10 min was used for improvement of conversion efficiency. Besides, 300 mg·L-1 timentin was the optimum antibiotics in transformation. PCR amplification exhibited that GUS gene has been successfully integrated into the chromosome of P. tenuiflora. Histochemical GUS staining and qRT-PCR analysis indicated that GUS gene has stably expressed with ß-glucuronidase activity in transgene seedlings. All these demonstrated that we have successfully established an Agrobacterium-mediated transformation system of P. tenuiflora, which provides a good platform for further gene function analysis and lays a solid foundation for molecular breeding.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-021-01247-8.