Genetic Transformation of Sugarcane, Current Status and Future Prospects

Abstract

Sugarcane (Saccharum spp.) is a tropical and sub-tropical, vegetative-propagated crop that contributes to approximately 80% of the sugar and 40% of the world’s biofuel production. Modern sugarcane cultivars are highly polyploid and aneuploid hybrids with extremely large genomes (>10 Gigabases), that have originated from artificial crosses between the two species, Saccharum officinarum and S. spontaneum. The genetic complexity and low fertility of sugarcane under natural growing conditions make traditional breeding improvement extremely laborious, costly and time-consuming. This, together with its vegetative propagation, which allows for stable transfer and multiplication of transgenes, make sugarcane a good candidate for crop improvement through genetic engineering. Genetic transformation has the potential to improve economically important properties in sugarcane as well as diversify sugarcane beyond traditional applications, such as sucrose production. Traits such as herbicide, disease and insect resistance, improved tolerance to cold, salt and drought and accumulation of sugar and biomass have been some of the areas of interest as far as the application of transgenic sugarcane is concerned. Although there have been much interest in developing transgenic sugarcane there are only three officially approved varieties for commercialization, all of them expressing insect-resistance and recently released in Brazil. Since the early 1990’s, different genetic transformation systems have been successfully developed in sugarcane, including electroporation, Agrobacterium tumefaciens and biobalistics. However, genetic transformation of sugarcane is a very laborious process, which relies heavily on intensive and sophisticated tissue culture and plant generation procedures that must be optimized for each new genotype to be transformed. Therefore, it remains a great technical challenge to develop an efficient transformation protocol for any sugarcane variety that has not been previously transformed. Additionally, once a transgenic event is obtained, molecular studies required for a commercial release by regulatory authorities, which include transgene insertion site, number of transgenes and gene expression levels, are all hindered by the genomic complexity and the lack of a complete sequenced reference genome for this crop. The objective of this review is to summarize current techniques and state of the art in sugarcane transformation and provide information on existing and future sugarcane improvement by genetic engineering.

Unraveling the population structure of the sugarcane borer,Diatraea saccharalis, in Argentina

“…In summary, results obtained in the present study generated important clarifications on the population genetic structure of D. saccharalis in South America, providing valuable information about routes of dispersal and the development of suitable management strategies. In that sense, the use of Bacillus thuringiensis (Bt) corn has been the primary tool for managing this species in corn fields (Fogliata et al, 2016); more recently also Bt sugarcane was commercially released in Brazil (Budeguer et al, 2021). However, as Bt crop technology is being threatened due to the selection of insecticide-resistant genotypes, understanding sugarcane borer genetic diversity and gene flow within and among its populations is especially important.…”

Genetic engineering: an efficient approach to mitigating biotic and abiotic stresses in sugarcane cultivation

“…82 On the other hand, traditional breeding for this trait is almost impossible due to the lack of herbicide-resistant genes in the genetics of wild relatives. 83 …”

“…Exhaustive studies concerning health and environmental regulations were performed to assess their potential impact on agricultural systems and food safety necessary for commercial deregulation of any transgenic event in Argentina. 83

Figure 1. Transgenic sugarcane varieties released for commercial use around the world.

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“…However, there are still many challenges before the commercial release of transgenic varieties resilient to these stresses. 83 The data in Table 1 show that it is mainly conducted under greenhouse conditions, so more studies on the field performance of a transgenic event are required to evaluate the possible effect on the stress tolerance capacity.…”

Genome Editing for Sustainable Crop Improvement and Mitigation of Biotic and Abiotic Stresses

“…A key approach in plant engineering for the past few decades has involved the integration of specifically assembled DNA cassettes or foreign genes into the host plant. The ability to express non-native segments of DNA in certain plants or crops resulted in novel plants with desirable traits such as herbicide resistance, pest resistance, and disease resistance [124]. It is also worth noting that transgene-free genome editing using the CRISPR/Cas-based system is rapidly becoming its main selling point to avoid unnecessary regulatory issues and to gain better public perception [125,126].…”