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A precise transformation protocol increases the infectivity of bacteria and causes receptor explants to absorb the infectious bacterial mixture sufficiently. This situation could increase the efficiency of genetic transformation significantly. Acetosyringone (AS) is a phenolic compound and can activate the vir gene in the plant expression vector, thus increasing the infectiousness of bacteria and the rate of transformation in monocots[34−37]. Hence, it must be added steadily at a suitable working concentration throughout bacterial cultivation. Sonication and vacuum treatment could induce receptor explants to absorb the infectious bacterial mixture sufficiently and enhance Agrobacterium-mediated transformation efficiency[38]. Herein, the sugarcane genetic transformation protocol could be established by combining influencing factors. The precise transformation protocol of our lab is as follows: The Agrobacterium strain harboring the target plant expression vector was streaked on YEP medium containing the appropriate antibiotics and 100 µM AS and grown at 28 °C for 3 d. Then, a single colony was selected and recultured overnight in liquid YEP medium containing the appropriate antibiotics and 100 µM AS at 28 °C. Subsequently, bacteria were collected after centrifugation, resuspended in a starter culture (1/5 strength MS medium + 30 g/L sucrose + 30 g/L glucose + 100 µM AS) and vortexed at 90–100 rpm for 2 h at 28 °C in the dark. Then, the bacterial mixture was diluted to an optical density of approximately 0.3–0.6 at 600 nm. A high density of the bacterial mixture may enhance transformation efficiency but also may induce the high copy number integration of the target genes. A suitable amount of embryogenic calluses (3–5 g) was collected and air dried on a clean bench. Then, the air-dried embryogenic calluses were transferred to an Erlenmeyer flask, added with approximately 50 mL of the bacterial mixture, and shaken slowly at 90–100 rpm for 10 min at 28 °C in the dark. In addition, the embryogenic calluses and bacterial mixture were sonicated (180 W) for 2 min in an ultrasonic cleaner. Then, the bacterial mixture was pipetted out, and 50 mL of fresh bacterial mixture was added again. Subsequently, the embryogenic calluses and bacterial mixture were vacuumed (−0.08 MPa) for 5 min then shaken slowly at 90–00 rpm for another 10 min at 28 °C in the dark. Afterward, the bacterial mixture was pipetted out, and the embryogenic calluses were blotted dry to remove excess Agrobacterium suspension and air-dried for approximately 30 min on a clean bench by using filter paper. Next, the embryogenic calluses were transferred to a Petri dish, sealed with parafilm, then incubated for 3 d at 21 °C in the dark. All of the infected embryogenic calluses were transferred to a resting medium without selection stress and cultured for 7 d at 28 °C in the dark. Subsequently, all embryogenic calluses were transferred to a selection medium containing 2 mg/L Basta (glufosinate ammonium) and cultured for 30 d at 28 °C in the dark. All selected calluses were transferred to a regeneration medium and cultured for 14 d (30 °C and 14 h of light and 28 °C and 10 h of darkness daily). After regeneration, green buds were transferred to a rooting medium and cultured for 30 d under the same conditions. Meanwhile, CFP expression was observed after resting cultivation (Fig. 1e), selection cultivation (Fig. 1f), regeneration cultivation (Fig. 1g, h), and rooting cultivation to estimate transformation efficiency. After rooting cultivation, resistant shoots were sampled for molecular assays via traditional PCR detection (Fig. 1i) and PAT/bar protein detection by using QuickStix Strips (Fig. 1j). The transformation results presented in Table 1 show that on average, 11 transgenic shoots could be obtained from each gram of embryogenic calluses used for transformation. The results of the PCR and QuickStix Strip assays demonstrated that almost 100% of the resistant shoots were positive.
Table 1. Technical service using the efficient transgenic system.
Name of
vector/geneCalluses
used (g)Transgenic shoots provided (lines) Target of genetic transformation Strategy of genetic modification Institutes serviced Date Cry2A 2 17 Pest-resistant genes OE Huazhong Agricultural University 2017.5 Cry1C 2 20 OE 2017.5 Hc-Pro 2 20 Functional gene of yje SCSMV virus OE Yangzhou University 2019.12 ScD27 2 20 Tiller-associated genes OE Sugarcane Research Institute, Yunnan Academy of Agriculture Science 2018.5 ScD10 2 25 RNAi 2019.6 INV 2 15 Sucrose invertase gene OE Institute of Nanfan & Seed Industry, Guangdong Academy of Science 2021.10 FUG 2 15 Haploidy induction gene GE 2019.12 SsWRKY1- OE 2 15 Drought resistance-associated genes OE Yunnan Agricultural University 2020.8 SsWRKY1-RNAi 2 20 RNAi 2020.8 DREB 2 12 Drought resistance-associated genes OE South Subtropical Crops Research Institute, Chinese Academy of Tropical Agriculture Science 2020.9 REMO 2 14 OE 2020.9 MYB8i 2 15 MYB transcription factors RNAi Fujian Agriculture and Forestry University 2020.11 MYB11i 2 12 RNAi 2020.11 ERF99 2 13 Ethylene-responsive factors OE 2020.11 Z6 3 45 JAZ transcription factors OE 2021.9 Z10 3 50 OE 2021.9 VSR 3 80 Vacuolar sorting receptors OE Yulin Normal University 2022.6 R1 3 35 Plant activator polypeptide receptor OE 2022.10 RK1 3 30 Ratoon stunting disease-responsive factors RNAi Sugarcane Research Institute, Guangxi Academy of Agriculture Science 2022.10 * OE: Target gene overexpression; RNAi: Target gene suppression by RNAi; GE: Gene mutation by genomic editing. -
The bar/Basta selection system was established in our laboratory by using the Agrobacterium-mediated genetic transformation method and a precise transformation protocol. It was proven to be an efficient genetic transformation system that enhanced the quality of induced sugarcane embryogenic calluses. Statistical analysis revealed that 10 or more transgenic shoots could be obtained from each gram of transformed embryogenic calluses used for transformation. In addition, resistant shoots 10 cm in height were obtained approximately 4 months from the initiation of the transformation. Screening revealed that the resistant shoots were almost 100% positive in the molecular assay. All transgenic shoots produced by our transformation system were herbicide-resistant and could be weed-controlled in field trials by using Basta (glufosinate ammonium) herbicide. We are working on the PMI/Mannose[20] and CP4-EPSPS/Roundup (unpublished) systems in our lab in addition to the efficient bar/Basta selection system. Transgenic shoots screened by the CP4-EPSPS/Roundup system are tolerant to Roundup (41% glyphosate), which is cheaper than Basta (20% glufosinate). Thus, the CP4-EPSPS/Roundup system has broad application prospects. By contrast, the released GM sugarcane lines from Brazil, namely, CTB141175/01-A, CTC91087-6, and CTC93209-4, were screened by the NPTII/ G418 and bar/Basta selection systems, and those from Indonesia, namely, NXI-1T, NXI-4T, and NXI-6T, were screened by using the NPTII/G418 and hpt/hygromycin-B selection systems. Therefore, our sugarcane transgenic system is the most advanced in the field. The other results (unpublished) of our research group also showed that our efficient sugarcane transgenic system was effective for ROC22, LC05-136, and GT42, which are the top three cultivated varieties in China. Our system also worked for S. spontaneum, which is an original parent of sugarcane. Thus, it may be effective for all sugarcane germplasms if high-quality embryogenic calluses could be induced. Numerous genome-edited sugarcane lines have also been created by combining genome-editing elements in plant expression vectors and delivering them to the genome by using our genetic transformation system. We produced numerous transgenic shoots of different research targets by using our transformation system and provided them to almost all sugarcane breeding institutes in China through technical services. Therefore, the establishment of our efficient sugarcane genetic transformation system has made a great contribution to the biological study and breeding of sugarcane in China.
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Cite this article
Wang W, Wang J, Feng C, Zhao T, Shen L, et al. 2023. Establishment of an efficient transgenic selection system and its utilization in Saccharum officinarum. Tropical Plants 2:11 doi: 10.48130/TP-2023-0011
Establishment of an efficient transgenic selection system and its utilization in Saccharum officinarum
- Received: 06 December 2022
- Accepted: 09 June 2023
- Published online: 19 July 2023
Abstract: Transgenic strategy plays an important role in the biological study and breeding of sugarcane. However, the efficiency of sugarcane transgenic systems remains disappointing to breeders. Various cultivated varieties are recalcitrant to genetic transformation, and only a few sugarcane research institutes could successfully obtain positive transgenic lines. In our previous research, three kinds of sugarcane transgenic selection systems, namely, the PMI/Mannose, CP4-EPSPS/glyphosate, and bar/Basta selection systems, were successfully established. Among these systems, the bar/Basta selection system was the most efficient. By applying this selection system, 10 or more transgenic shoots could be obtained from a gram of embryogenic calluses. In addition, the resistant shoots obtained after screening were almost 100% positive for the molecular assay, and all of the transgenic shoots showed high herbicide tolerance in lab tests and field trials. Herein, the key points/steps, advantage and contribution to sugarcane studies and breeding in China of the efficient bar/Basta sugarcane transformation system are presented and discussed.
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Key words:
- Sugarcane /
- Genetically modified /
- Screening system /
- Agrobacterium-mediated /
- Herbicide tolerance /
- bar gene