Efficient Agrobacterium tumefaciens-mediated stable genetic transformation of green microalgae, Chlorella sorokiniana

The green oleaginous microalgae, Chlorella sorokiniana, is a highly productive Chlorella species and a potential host for the production of biofuel, nutraceuticals, and recombinant therapeutic proteins. The lack of a stable and efficient genetic transformation system is the major bottleneck in improving this species. We report an efficient and stable Agrobacterium tumefaciens-mediated transformation system for the first time in C. sorokiniana. Cocultivation of C. sorokiniana cells (optical density at λ ₆₈₀ = 1.0) with Agrobacterium at a cell density of OD₆₀₀ = 0.6, on BG11 agar medium (pH 5.6) supplemented with 100 μM of acetosyringone, for three days at 25 ± 2 °C in the dark, resulted in significantly higher transformation efficiency (220 ± 5 hygromycin-resistant colonies per 10⁶ cells). Transformed cells primarily selected on BG11 liquid medium with 30 mg/L hygromycin followed by selecting homogenous transformants on BG11 agar medium with 75 mg/L hygromycin. PCR analysis confirmed the presence of hptII, and the absence of virG amplification ruled out the Agrobacterium contamination in transformed microalgal cells. Southern hybridization confirmed the integration of the hptII gene into the genome of C. sorokiniana. The qRT-PCR and Western blot analyses confirmed hptII and GUS gene expression in the transgenic cell lines. The specific growth rate, biomass doubling time, PSII activity, and fatty-acid profile of transformed cells were found similar to wild-type untransformed cells, clearly indicating the growth and basic metabolic processes not compromised by transgene expression. This protocol can facilitate opportunities for future production of biofuel, carotenoids, nutraceuticals, and therapeutic proteins.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02750-7.

Agrobacterium Transformation in the Rice Genome

Modification of the rice genome by Agrobacterium-mediated transformation is a general technique that can be easily performed today. Successful methods were established by vigorous studies on the culture system and the elucidation of Agrobacterium transformation mechanisms. This section provides a detailed description of routine and efficient rice transformation protocols by Agrobacterium. This method uses mature seeds as a material and can be applied to many japonica and some other varieties of rice. According to this method, it is even possible for beginners to obtain rice transformants.

Agrobacterium-Mediated Transformation of Wheat Using Immature Embryos

Methods of the Agrobacterium-mediated transformation of bread wheat (Triticum aestivum L.) have been improved in recent years so that genetic engineering can be routinely used for functional genomics as well as for wheat breeding. In the protocol described here, immature embryos of the spring-type model genotype Bobwhite SH 98 26 have been used. Preculture and temperature pretreatment of these explants have led to the reproducible generation of transgenic plants at efficiencies between 5 and 15%. Whereas primary transgenic plants regenerated in vitro commonly show reduced fitness and fertility, no apparent variations with regard to morphology and grain set in their transgenic progeny as compared to wild-type counterparts were observed.

Efficient and heritable transformation of Phalaenopsis orchids

BACKGROUND

Phalaenopsis orchid (Phal. orchid) is visually attractive and it is important economic floriculture species. Phal. orchids have many unique biological features. However, investigation of these features and validation on their biological functions are limited due to the lack of an efficient transformation method.

RESULTS

We developed a heritable and efficient Agrobacterium- mediated transformation using protocorms derived from tetraploid or diploid Phal. orchids. A T-DNA vector construct containing eGFP driven by ubiquitin promoter was subjected to transformation. An approximate 1.2-5.2 % transformation rate was achieved. Genomic PCR confirmed that hygromycin selection marker, HptII gene and target gene eGFP were integrated into the orchid genome. Southern blotting indicated a low T-DNA insertion number in the orchid genome of the transformants. Western blot confirmed the expression of eGFP protein in the transgenic orchids. Furthermore, the GFP signal was detected in the transgenic orchids under microscopy. After backcrossing the pollinia of the transgenic plants to four different Phal. orchid varieties, the BC1 progenies showed hygromycin resistance and all surviving BC1 seedlings were HptII positive in PCR and expressed GFP protein as shown by western blot.

CONCLUSIONS

This study demonstrated a stable transformation system was generated for Phal. orchids. This useful transformation protocol enables functional genomics studies and molecular breeding.

Hygromycin resistance is an effective selectable marker for biolistic transformation of black spruce (Picea mariana)

 Using particle bombardment of mature somatic embryos followed by the induction of secondary embryogenesis in the presence of hygromycin, we produced over 90 lines of transgenic embryonal masses expressing β-glucuronidase from two genotypes of black spruce. Transformation efficiencies of up to 7% (1 transgenic line per 14 embryos bombarded) were achieved by extending the period of selection from 8 to 12 weeks. Proliferation of transformed embryonal masses in the presence of hygromycin had no effect on either embryogenicity or embryo maturation. Southern blot hybridization and PCR amplification confirmed the presence of the hygromycin phosphotransferase gene in genomic DNA. The expression of the β-glucuronidase gene in the needles of regenerated seedlings support the potential for long-term transgene expression in spruce.