Introduction
With the growing world population and changing climate conditions,
feeding the world in the future will pose a severe challenge (Dhankher
and Foyer 2018; Ray et al . 2013). Global food, feed, and fuel
requirements are putting tremendous stress on our limited land
resources. To achieve food safety and security goals, utilizing degraded
and contaminated land for agricultural production safely and sustainably
will assist in feeding the future population. Heavy metals and
metalloids are major contributors to soil contamination (Li et
al . 2019). Metal(loid)s such as arsenic (As) can be present naturally
in agricultural soil or due to anthropogenic activities like fertilizer
and pesticide application, sewage waste, coal burning, and industrial
pollution (Li et al . 2019). The presence of metal(loid)s in soil
impacts the growth and development of food crops as these toxic elements
compete with nutrient uptake, negatively impact photosynthesis, create
reactive oxygen species (ROS), and damage crucial biochemical processes
in plant cells (Farooq et al . 2016; Li et al. 2019). Besides
severely impacting food production, toxic metals also affect food
quality and safety. Food contaminated with toxic metals poses serious
threats to the health of humans and livestock. Chronic exposure to As
can cause skin, liver, and kidney cancer (Farooq et al . 2016;
Jomova et al . 2011), mercury (Hg) exposure leads to nervous
system damage (Yang et al . 2020), cadmium (Cd) can cause kidney
diseases and cancers (Genchi et al . 2020), and lead (Pb) causes
reduced cognitive skills and mental development issues (Mason, Harp, and
Han 2014). In order to utilize degraded land resources, we need to
develop strategies for the safe use of contaminated sites without
compromising the quality and quantity of the produce grown on them. One
such approach is utilizing genetic engineering to create plants that can
withstand phytotoxicity while limiting the uptake and accumulation of
toxic metals.
One of the significant toxic metalloids of global concern is As. Arsenic
is a highly toxic, group I carcinogen, and unlike some heavy metals like
iron, nickel, and cobalt, it is not required by plants (Farooq et
al . 2016). Globally, As contamination is a major concern in
~108 countries, impacting more than 230 million people
(Shaji et al . 2021). Arsenic toxicity also reduces plant growth
and development by damaging the plant’s cellular and molecular functions
(Meselhy et al . 2021; Verma et al . 2021). Plants can take
up As in two primary forms – inorganic forms such as arsenite (AsIII)
and arsenate (AsV), and organic forms such as methylated arsenic
–monomethylarsenic acid (MMA) and dimethylarsenic acid (DMA) (Bali and
Sidhu 2021; Farooq et al . 2016). Plants take up inorganic AsV
through phosphate transporters and AsIII, MMA, and DMA via
membrane-bound aquaporin transporters, like nodulin 26-like proteins
(NIPs) and plasma membrane intrinsic proteins (PIPs) (Ali 2022; Farooqet al . 2016; Mosa et al . 2012). After entering plants, As
impacts the plants’ physiology and biochemistry by hindering
photosynthetic, respiratory, and other growth and development processes.
To protect themselves from the damaging effects of As and other toxic
metals, plants utilize their innate capability to detoxify toxic
metal(loid)s efficiently via binding with glutathione (GSH) and GSH
derivatives, phytochelatins (PCs). Plant cells maintain GSH homeostasis
via the γ-glutamyl cycle (Paulose et al. , 2013; Noctor et
al. , 2012; Emamverdian et al. , 2015; Hasanuzzaman et al. ,
2017). Glutathione and its oligomer PCs can help sequester heavy metals
in the vacuole and extracellular spaces and limit their uptake and
transport, thereby preventing the plant’s cellular machinery from
damaging toxic effects (Hasanuzzaman et al. 2017). Exogenous GSH
application has improved plant tolerance to Hg, cesium (Cs), silver
nanoparticles (AgNPs), and salinity in Arabidopsis, soybean, and poplar
(Adams et al . 2020; Akram et al . 2017; Kim et al .
2017; Ma et al . 2020). Moreover, improving GSH synthesis via
overexpression of the GSH1 gene showed increased tolerance to Cd
and As in Arabidopsis (Guo et al . 2008) and enhanced tolerance to
Pb in poplar (Samuilov et al . 2016) and better overall growth of
poplar grown in soil contaminated with heavy metals (Ivanova et
al . 2011). Overexpression of bacterial γ-ECS, a GSH1homolog, also leads to increased tolerance to As in Arabidopsis
(Dhankher et al. 2002; Li et al. 2005). Similarly,
overexpressing GSH recycling genes, GGCT2;1 (gamma-glutamyl
cyclotransferases 2;1 ), improved tolerance to As in Arabidopsis which
led to higher biomass, lower As accumulation, and better nutrient
utilization as compared to wild-type plants (Paulose et al.2013). Here, we translate those Arabidopsis research findings of Pauloseet al. (2013) into Camelina sativa , a biofuel crop, to
potentially develop plants that can provide economic returns while
cultivated on soils contaminated with toxic metals.
The selection of Camelina as the crop to work with was based on its
unique properties. Camillina sativa , commonly known as the gold
of pleasure or false flax, is an oilseed crop of the Brassicaceae family
and is considered a dedicated biofuel crop (Chhikara et al .
2018). Camelina has various agronomic advantages for production,
including early maturity, low requirement for water and nutrients,
adaptability to adverse environmental conditions, and resistance to
common cruciferous pests (Abdullah et al . 2018; Kagale et
al . 2014; Stamenković et al . 2021). Camelina seeds contain more
than 30% oil which can be utilized to produce biodiesel. Based on its
shorter life cycle (85-100 days), it can be included in double and relay
cropping systems. Life cycle assessment studies of Camelina have shown
its economic viability and sustainability for use as a biofuel (Bertiet al . 2017; Keske et al . 2013). However, Camelina is
still an underutilized resource, and its potential as a biofuel crop
could be increased by translating and applying beneficial research
findings from other model plants (Sainger et al . 2017;
Stamenković et al . 2021).
In congruence with this aim to improve Camelina, as a translational
approach, we overexpressed the CsGGCT2;1 gene in Camelina and
analyzed its effect on the plant’s ability to grow on
arsenite-contaminated media. Our results showed that overexpression ofCsGGCT2;1 enabled Camelina plants to grow better than wild-type
(WT) plants on media supplemented with AsIII. The CsGGCT2;1transgenic lines also had significantly higher shoot and root biomass,
improved chlorophyll content, lower lipid peroxidation, and lower
arsenic accumulation than WT plants.