1   Uptake Rate

As shown in the figure below, zucchini has shown an impressive absorbance ability of dioxins from contaminated soil1¹. The main advantage zucchini and pumpkin plants have over other plants (that have been studied) are their ability to transfer the dioxins to their shoots, flowers, and fruits, while others cannot², so theoretically we have more dioxin to mass ratio, letting them absorb more dioxins. As such, zucchini and pumpkin are our main candidates for dioxin phytoremediation in case of a suitable climate.

Fig. 1: "Mean decreases in total and TEQ PCDD/PCDF concentrations in soil amended with different doses of sewage sludge (A1, A2) and urban sediments (B1–B2) before and after Cucurbita pepo L. cv ‘Atena Polka’ cultivation".³

2   Growth Conditions

Zucchini and pumpkin are very sensitive to cold weather, requires warm temperatures of above 16 degrees Celsius to grow, but to warm of a climate (above 38 degrees) will harm the plant. Zucchini takes about 60 days to mature. By then it produces fruit as long as someone picks them before they rot. Pumpkin requires between 90 to 160 days to mature. They both grow relatively quickly and, as such, have high root-uptake of nutrition from the ground. Both require moderate quantities of water to grow, which may make it more difficult to grow in drier climates; however, pumpkins have been successfully grown in Iraq, for example. Zucchini roots generally extend deeply downward in a taproot formation, while pumpkin roots tend to spread horizontally as well as vertically - most of its nutrients are absorbed from the upper 1/2 meter of the soil. ^3,4,5

3   Plant Transformation:

We know of a few agrobacterium strains able to transform pumpkin plants and zucchini^6,7. Agrobacterium is one of the most popular methods of plants transformation, widely studied in plant research. 

4   Plant Sterility

Triploid plants^* have larger organs, greater biomass, and strong stress resistance by preserving relatively larger amounts of photosynthetic energy⁸. The undesirable spread of non-native invasive crop and horticultural plants into natural areas can also be reduced or eliminated by the use of triploids because they tend to be sterile and seedless There are few different ways to create triploid plants:

• - Natural selection - triploid plants occur in nature, meaning it is possible to look for the desired plant in nature.
• - Artificial hybridization - by sexual hybridization of different ploidy, one can create a triploid offspring.
• - Endosperm culture in vitro - endosperm is a triploid tissue. Successful regeneration of a plant from an endosperm tissue would result in a triploid plant.

• Triploid plants contain 3 sets of chromosomes, meaning they have 3n chromosomes. Triploid organisms, in general, tend to be sterile, as in most plants.

Optimized genes for Cucurbita pepo:

View sequences

* In order to optimize the genes, we used our MOOLTi codon optimizer. We originally designed MOOLTi to perform optimizations for multiple organisms simultaneously, but it is also capable of optimizing for a single organism with ease.

References:

1. "Potential for Phytoremediation of PCDD/PCDF-Contaminated Sludge and Sediments Using Cucurbitaceae Plants: A Pilot Study" Magdalena Urbaniak et al. (2016).
2. "Uptake by roots and translocation to shoots of polychlorinated dibenzo-p-dioxins and dibenzofurans in typical crop plants" Haijun Zhang et al. (2009).
3. "Planting, growing, and harvesting pumpking" The Old Farmer'S Almanac website (2010).
4. "How to Grow Zucchini: A Squash Vocabulary Lesson" Charity Shumway (2012).
5. "What Is the Life Expectancy of Zucchini Plants?" Karen Carter.
6. "Cucurbita pepo L. can be transformed by Agrobacterium rhizogenes" Luigi Sanità di Toppi et al. (1997).
7. "A simple method for transient transformation of pumpkin (Cucurbita maxima) seedlings" Francisco Arturo Ramírez-Ortega et al. (2015).
8. "Breeding Triploid Plants: A Review" Xiling Wang et al. (2016).

1   Uptake Rate

Much like the Chinese cabbage, tomato plants have high dioxin uptake in their roots but very poor transfer to shoots through the xylem². The main difference between the two [plants] is higher root uptake in Chinese cabbage, while tomatoes have an easier transformation and longer life expectancy.

2   Growth Conditions

Tomato plants come in different sizes and varieties. Tomato plants are perennials, mostly requiring direct sunlight to grow and love warm temperatures, able to grow in most areas of the world. It`s roots form a taproot formation, reaching half a meter to a meter and a half deep and 1 meter in diameter.

3   Plant Transformation:

Plant transformation using agrobacterium is considered robust, with transformation frequencies of 40%+³. On top of that, a whole genome sequence, being continuously studied for several decades now, gives us superb knowledge of tomato transformation possibilities.

4   Plant Sterility

A technique for promoting fruit formation without seed creation using CRISPR/Cas9 exists⁴ as well as known male and female sterile strains⁵. On the downside, the plant is known for its ability to form roots everywhere on its stem, meaning it can easily spread by vegetative means.⁶

Optimized genes for Solanum lycopersicum:

View sequences

* In order to optimize the genes, we used our MOOLTi codon optimizer. We originally designed MOOLTi to perform optimizations for multiple organisms simultaneously, but it is also capable of optimizing for a single organism with ease.

References:

1. "Tomato gene sequence" Fernandez-Pozo et al (2014).
2. "Uptake by roots and translocation to shoots of polychlorinated dibenzo-p-dioxins and dibenzofurans in typical crop plants" Haijun Zhang et al. Chemosphere; Volume 76, Issue 6, Pages 740-746 (2009).
3. "A simple and efficient Agrobacterium-mediated procedure for transformation of tomato" Sharma MK and Sharma AK (2009).
4. "Rapid breeding of parthenocarpic tomato plants using CRISPR/Cas9" Risa Ueta et al. Scientific Reports; volume 7, Article number: 507 (2017).
5. " SEXUAL STERILITY is Essential for Both Male and Female Gametogenesis in Tomato." Hao S et al. Plant Cell Physiol 58(1):22–34 (2017).
6. "Planting, growing, and harvesting tomatoes" The Old Farmer's Almanac website (2018).