Plastid Transformation: How Does it Work? Can it Be Applied to Crops? What Can it Offer?

Abstract

<jats:p>In recent years, plant genetic engineering has advanced agriculture in terms of crop improvement, stress and disease resistance, and pharmaceutical biosynthesis. Cells from land plants and algae contain three organelles that harbor DNA: the nucleus, plastid, and mitochondria. Although the most common approach for many plant species is the introduction of foreign DNA into the nucleus (nuclear transformation) via Agrobacterium- or biolistics-mediated delivery of transgenes, plastid transformation offers an alternative means for plant transformation. Since there are many copies of the chloroplast genome in each cell, higher levels of protein accumulation can often be achieved from transgenes inserted in the chloroplast genome compared to the nuclear genome. Chloroplasts are therefore becoming attractive hosts for the introduction of new agronomic traits, as well as for the biosynthesis of high-value pharmaceuticals, biomaterials and industrial enzymes. This review provides a comprehensive historical and biological perspective on plastid transformation, with a focus on current and emerging approaches such as the use of single-walled carbon nanotubes (SWNTs) as DNA delivery vehicles, overexpressing morphogenic regulators to enhance regeneration ability, applying genome editing techniques to accelerate double-stranded break formation, and reconsidering protoplasts as a viable material for plastid genome engineering, even in transformation-recalcitrant species.</jats:p>

Organelle Genetics in Plants

“…In this Special Issue “Organelle Genetics in Plants,” 11 articles were accepted with four reviews and seven original research articles covering outstanding advances in different chloroplast and plant mitochondria research fields ( Table 1 ). These works focus on topics related to organellar gene expression (OGE) (chloroplast RNA editing in soybean [ 5 ], mitochondria RNA editing and intron splicing in soybean during nodulation [ 6 ] and the roles of transcriptional and post-transcriptional regulation of OGE in responses to environmental stress [ 7 , 8 ]); the analysis of nuclear integrants of mitochondrial DNA (NUMTs) or plastid DNA (NUPTs) [ 9 ]; the sequencing and characterization of organellar genomes (the mitogenomes of common bean [ 10 ] and four Trifolium species [ 11 ], and the chloroplast genomes (plastomes) of Trentepohlia odorata [ 12 ], three Utricularia amethystina morphotypes [ 13 ], and three plant parasitic Macrosolen species [ 14 ]); and finally, the most recent advances in plastid genome engineering [ 15 ]. In this editorial, we sum up the main findings of these eleven insightful manuscripts.…”

“…Finally, Yu et al [ 15 ] review the current status of plastid transformation, a technical approach that is drawing more attention in order to develop new genetically engineered crops. Among the benefits of chloroplast transformation vs. nuclear transformation, the many copies of the plastome that chloroplasts contain, and the many chloroplasts that a plant cell usually harbors, must be highlighted.…”

Advantage of Nanotechnology-Based Genome Editing System and Its Application in Crop Improvement

“…Along with biolistic methods, PEG-mediated transformation is one of the most commonly used methods for introducing genetic cargo into chloroplasts (Yu et al, 2020). This method enables the carrying of several genetic cargo types, such as DNA and RNAs (small interfering RNA [siRNA] and miRNA; Cunningham et al, 2018).…”

Advancing organelle genome transformation and editing for crop improvement

“…Engineering of the plastome was first accomplished in Chlamydomonas reinhardtii , a unicellular green alga ( Boynton et al., 1988 ), and in the higher plant tobacco ( Nicotiana tabacum ), a dicotyledonous flowering species ( Svab et al., 1990 ). Since then, the technique of plastid transformation has been extended to over 20 species of flowering plants ( Ahmad et al., 2016 ; Yu et al., 2020 ); however, reproducible protocols for achieving homoplastic offspring are currently limited to a handful of species, including tobacco, potato, tomato, cabbage, soybean, lettuce ( Bock, 2015 ), poplar ( Okumura et al., 2006 ; Wu et al., 2019 ; Xu et al., 2020 ), and licorice weed ( Muralikrishna et al., 2016 ; Kota et al., 2019 ). Cereals, the world's most important food crops, are recalcitrant to chloroplast transformation, mainly owing to the lack of a suitable selectable system, efficient shoot regeneration frequency, and cis -elements for transgene expression in non-green plastids.…”