Effect of Spaceflight and Simulated Microgravity on Plant Defense Responses (Plant Habitat-06)

Plants on Earth and in space must defend themselves from diseases. Effect of Spaceflight and Simulated Microgravity on Plant Defense Responses (Plant Habitat-06) investigates the physiological and genetic responses to defense activation and immune system function in tomatoes during spaceflight. Genetic sequencing and analyses indicate the adaptive response of plants rather than the initial defensive response. A better understanding of how microgravity affects plant immune function is needed to support plant growth and food production on future space missions.

Delivery of investigation to the International Space Station (ISS) via the SpaceX-29 Commercial Resupply Service mission in November, 2023.

The Effect of Spaceflight and Simulated Microgravity on Plant Defense Responses (Plant Habitat-06) investigation studies the physiological and whole genome transcriptional responses to defense activation in wild-type and immune-deficient tomatoes during spaceflight. The tomatoes are grown in the Advanced Plant Habitat (APH) facility. Defense responses are activated with a chemical elicitor and plant hormone, salicylic acid. At 24 and 48 hours after defense activation, plant tissues are harvested and preserved in cold stowage aboard the International Space Station. Images of all plants are taken daily to provide a record for researchers to study the impact of spaceflight on growth rates of immune-activated and immune-deficient tomatoes. All investigations are also performed in parallel on the ground.

Upon sample return to Earth, next-generation sequencing is performed to identify genome-wide transcriptional defense responses. In addition, next-generation sequencing is used to examine the transcriptional response to spaceflight in immune-deficient tomatoes. Total RNA is extracted from each sample using TRIZOL. At approximately three-weeks post germination, RNA yields of more than 1 μg from one tomato leaf are harvested. RNA quality is assessed by a Bioanalyzer at the Purdue Genomics Facility, and only RNA with a RNA Integrity Number (RIN) score above 7 is used for downstream analyses. Up to 1 μg total RNA from each of 56 samples is sent to Purdue’s Genomics Facility for paired end 150 bp sequencing on the Illumina HiSeq 2500. Data is mapped to the tomato genome using TopHat. Differentially expressed genes are identified using the DESeq2 package in R. Genes with a log fold change greater than 1.5 and a false-positive rate of q < 0.01 are considered differentially expressed. Ten differentially expressed genes with known relationships to plant defenses are validated using RT-qPCR. To promote accessibility, RNA-sequencing data are deposited in NASA’s GeneLab upon publication.

Results add to fundamental knowledge of how the plant immune system adapts to spaceflight and how spaceflight affects plant production. Results also provide insight for future experiments aimed at understanding crop immune system function in spaceflight.

Plant pathogens are responsible for 20 to 40% of global crop loss on Earth. This study could uncover new interactions between gravity and plant responses to pathogens and support development of new resistance strategies to protect plants and enhance crop growth and productivity on Earth.

Space Station Research Explorer