When we first started the project, it was unclear if the SPACE phenotype was a result of transformation or can be reproduced anytime. During the project we demonstrated that SPACE tomatoes can be cultivated reproducibly both in vitro and in soil. The SPACE phenotype can manifest from seed germination or from tissue culture regeneration. Mutant plants were genotyped and two mutant genotypes were identified that lead to the SPACE phenotype. We also isolated homozygous lines from the T1 and T2 plants. A qPCR protocol was established to facilitate rapid genotyping of plants. Mutant plants were grown and their phenotypes determined. Harvest index, a plant productivity metric used to describe the relative distribution of biomass between the edible and inedible components of a crop (Hay, 1995), was determined for both wildtype and SPACE tomato plants. The SPACE tomato plants have an almost 30% increase in harvest index. We measured other physiological metrics such as time to fruit, flowering history, flower bud history, fruiting history, height, leaf number, and senescent leaves history. From all of this data we performed two rounds of selection of the inbred lines to select those with the most desirable traits. Currently we are at the T4 generation. From these selected lines, plant growth was scaled up to allow us to grow a large number of plants to generate seed stock and evaluate the fruit. We performed tests to evaluate the SPACE tomato fruit for nutrient levels and palatability. No difference was found between SPACE tomato fruit and wildtype tomato fruit, suggesting that decreases in plant size do not alter fruit taste or nutrient levels. To increase CO2 fixation in the SPACE plants we have prepared plasmids with genes from algae that are key for the algal carbon concentrating mechanism. These algal genes have been transformed into plants but could not be evaluated before the end of the grant due to delays resulting from COVID-19. Overall these findings have helped to move SPACE tomatoes towards being a viable plant for cultivation during space flight.

The future for the SPACE tomato project is promising. In the last year, our proposal to grow the SPACE tomatoes on the ISS in in the Advanced Plant Habitat was selected by NASA Space Biology. This grant, starting March 1, 2021, aims to demonstrate a seed-to-seed growth experiment on the ISS, an important step towards crop systems in space. Here on Earth the SPACE tomatoes will be evaluated for use in vertical controlled environment agriculture. We received a three-year grant from the Foundation for Food and Agriculture Research (FFAR) to evaluate SPACE tomatoes in vertical farms. Additionally, several vertical agriculture companies have expressed interest in licensing the SPACE tomatoes and in forming collaborations with us to conduct growth trials of the plants in their vertical farms.

Reference:

Hay RKM. Harvest index: a review of its use in plant breeding and crop physiology. Annals of Applied Biology. 1995 Feb;126:197-216.

Plants on space expeditions can provide a fresh source of food and nutrients, carbon dioxide uptake capacity, and behavioral health benefits to crew members. Most fruit and vegetable bearing plants are too large and produce too much inedible biomass for space flight applications. This has limited plants grown in space to leafy green vegetables, such as lettuce. Increasing the diversity of plants suitable for space flight would increase nutritional opportunities and increase the diversity of fresh food options available for crew members. We have developed a genetically engineered tomato plant that is altered in its developmental cycle that is ideal for growth in space flight applications. These plants grow minimal amounts of leaves, flower, and develop fruit in rapid progression. These tomato plants have several traits that make them ideal for cultivation on a spacecraft: (1) small size, (2) very small amount of non-edible biomass produced, and (3) the ability to produce fruit faster.

This project aims to (1) develop this trait, which we are calling Small Plants for Agriculture in Confined Environments (SPACE), in tomatoes and determine the feasibility of these plants to be grown on the International Space Station (ISS) in NASA's Vegetable Production System (Veggie), (2) engineer key components of an algal carbon concentrating mechanism into SPACE tomato plants to increase carbon capture and growth rates, and (3) evaluate nutrient levels, palatability, and microbial loading levels of SPACE tomato fruit grown in simulated ISS conditions.

When we first started the project, it was unclear if the SPACE phenotype was a result of transformation or can be reproduced anytime. We have been able to show that SPACE tomatoes can be cultivated reproducibly both in vitro and in soil. The SPACE phenotype can manifest from seed germination or from tissue culture regeneration. Growing the plants in soil has allowed us to grow up large numbers of plants to generate seed stock. Mutant plants were genotyped and two mutant genotypes were identified that lead to the SPACE phenotype. We also isolated homozygous lines from the T1 and T2 plants. A qPCR protocol was established to facilitate rapid genotyping of plants. Mutant plants were grown and their phenotypes determined. Harvest index, a plant productivity metric used to describe the relative distribution of biomass between the edible and inedible components of a crop (Hay, 1995), was determined for both wildtype and SPACE tomato plants. The SPACE tomato plants have an almost 30% increase in harvest index. We measured other physiological metrics such as time to fruit, flowering history, flower bud history, fruiting history, height, leaf number, and senescent leaves history. To increase CO2 fixation in the SPACE plants we have prepared plasmids with genes from algae that are key for the algal carbon concentrating mechanism. These findings will help move SPACE tomatoes towards being a viable plant for cultivation during space flight.

In the next year we plan on continue phenotyping SPACE tomatoes to better understand how these plants produce fruit in simulated ISS conditions. We will transform algal carbon concentration genes into SPACE tomatoes and then assess if they increase rates of photosynthesis and carbon fixation. And we will grow SPACE tomatoes under simulated ISS conditions and then evaluate fruit for nutrient levels, palatability, and microbial loading levels. Our ultimate goal with this project is to evaluate SPACE tomatoes on the ISS.

Reference: Hay RKM. Harvest index: a review of its use in plant breeding and crop physiology. Annals of Applied Biology. 1995 Feb;126:197-216.