The Lunar Green Revolution: Introduction

Introduction:

Paul et al., (2022) investigated the ability of plants to grow in lunar regolith and utilize it as a resource for life support in lunar habitats. Using the terrestrial plant Arabidopsis thaliana and samples from Apollo 11, 12, and 17, they found that the plants were able to germinate and grow in diverse lunar regoliths, but growth was challenging and many showed severe stress morphologies. Furthermore, all plants grown in lunar regoliths showed differential gene expression indicating ionic stresses similar to plant reactions to salt, metal, and reactive oxygen species (ROS). Therefore, while lunar regoliths can be useful for plant production in lunar habitats, they are not benign substrates, and further research is needed to elucidate the interaction between plants and lunar regolith and mitigate any negative effects. This study provided important insights into the potential use of in-situ resources for life support on other worlds, particularly the Moon.

The Green Revolution of the 1960s saw significant increases in cereal crop yields, primarily due to the introduction of high-yielding varieties of wheat and rice. The incorporation of dwarfing genes into these plants was crucial to this revolution as tall plants were unable to support the weight of the heavy grain and tended to lodge, causing significant yield losses. Dwarfing genes resulted in shorter, stronger stalks that did not lodge and increased the amount of assimilate partitioned into the grain, leading to further yield increases. The genes responsible for this semi-dwarf growth habit have now been identified as the Reduced height (Rht) genes in wheat and the semi-dwarf1 (sd1) gene in rice. These genes interfere with the signal transduction pathway of the gibberellin (GA) growth hormone, which plays a central role in controlling plant stature. The dwarfing genes in wheat are semi-dominant alleles of homologous genes on chromosomes B and D, while the dwarfing gene in rice was identified as a defective enzyme in the GA biosynthetic pathway. These genes have been incorporated into many wheat and rice cultivars worldwide and have had a significant positive impact on global food production. However, these dwarf wheat crops are potentially more likely to have difficulty growing in lunar regolith.

The Green Revolution has led to a significant increase in grain yield, but this has come at the cost of nitrogen use efficiency (NUE). NUE is the amount of nitrogen that is absorbed by plants and used for growth and development, relative to the amount of nitrogen that is applied. High-yield crops typically have lower NUE than low-yield crops. Gibberellin (GA) signalling is a key factor in regulating plant growth and development. GAs are hormones that control a wide range of plant processes, including nitrogen uptake. GAs also play a role in the regulation of chromatin, which is the packaging of DNA in the nucleus. Chromatin modulation can affect gene expression, and GAs can alter chromatin in a way that promotes the expression of nitrogen-responsive genes.

The mechanisms underlying the cross-talk between GA- and nitrogen-responsive gene networks are starting to be unravelled. This information could be used to develop new strategies for increasing NUE in crops. One possibility is to manipulate the GRF4-DELLA-NGR5 module (Wu et al., 2021). This module is involved in the regulation of both GA signalling and chromatin modulation. By manipulating this module, it may be possible to increase NUE without sacrificing grain yield. The development of new strategies for increasing NUE is essential for the future of agriculture. As the world's population continues to grow, the demand for food will also increase. In order to meet this demand, we need to develop sustainable ways of producing food. Increasing NUE is one way to achieve this goal.

When Paul et al.,(2022) looked at the gene expression data based on the plants' growth success rather than the specific location they were grown in, they found that even the plants that appeared more successful (similar in size and shape to those grown in JSC-1A simulant) had transcriptomes indicative of strong stress response. The plants were categorized into three phenotypic groups of three plants each: "Severe" (small with distorted shape and reddish-black pigmentation throughout), "Small" (small but green and proportionate), and "Large" (larger than other regolith-grown plants, with normal pigmentation and shape, similar to JSC-1A phenotype, but still smaller than JSC-1A-grown plants). These phenotypes resemble those of GA dwarf mutants, which have similar slow growth, developmental delays and morphology defects due to a mutation in the gibberellin hormone pathway or downstream via mutation in GA receptors or the DELLA proteins they regulate via tissue-specific patterns of ubiquitin E3 ligase targeted degradation. Molecular and physiological studies have demonstrated that DELLA proteins, which were once considered as master negative regulators of GA signalling, actually integrate multiple hormone signalling pathways through physical interactions with transcription factors or regulatory proteins from different families.

Paul et al., (2022), also analyzed the transcriptomes of plants grown in lunar regolith from different Apollo sites to better understand the basis of their stress morphologies. They found that plants grown in Apollo 11 regolith showed the most differentially expressed genes (DEGs), followed by Apollo 12 and Apollo 17. All lunar samples evoked DEGs associated with ABA signalling, salt, metal, and reactive oxygen species stresses, with a strong representation of nutrient metabolism genes. The most highly induced and repressed DEGs were associated with phosphate and nitrogen starvation. Plants from each Apollo sample also differentially expressed genes unique to each site, indicating a discernable and distinguishing plant response based on lunar regolith sample. The results suggest that plant responses vary based on the lunar regolith source and that lunar regolith is more stressful than JSC-1A simulant. However, they observed a range of growth success states within each lunar regolith sample, indicating the potential for successful plant growth in the lunar regolith.

Ref-> https://www.sciencedirect.com/science/article/abs/pii/S1369526621000741?via%3Dihub

Figure XX: Stable diffusion used to help imagine an underground robotic farm that uses light to convert regolith into biomass. Engineering the environment “Amending the soil structure”. Engineering the genetics of future lunar permaculture programs.