a display of phenotypic plasticity. On the Moon On January 2, 2019, China's Chang'e-4 lander brought A. thaliana to the moon. A small microcosm 'tin' in the lander contained A. thaliana, seeds of potatoes, and silkworm eggs. As plants would support the silkworms with oxygen, and the silkworms would in turn provide the plants with necessary carbon dioxide and nutrients through their waste, researchers will evaluate whether plants successfully perform photosynthesis, and grow and bloom in the lunar environment. Secondary metabolites is an Arabidopsis root triterpene. Potter et al., 2018 finds synthesis is induced by a combination of at least 2 facts, cell-specific transcription factors (TFs) and the accessibility of the chromatin. Plant–pathogen interactions Understanding how plants achieve resistance is important to protect the world's food production, and the agriculture industry. Many model systems have been developed to better understand interactions between plants and bacterial, fungal, oomycete, viral, and nematode pathogens. A. thaliana has been a powerful tool for the study of the subdiscipline of plant pathology, that is, the interaction between plants and disease-causing pathogens. [[File:ArabidopsisPlantPathology.jpg|thumb|upright=2|Components of pathogen recognition in A. thaliana 'A schematic of PAMP-triggered immunity, to be specific recognition of flagellin by FLS2 (top left), effector-triggered immunity depicted through the recognition of avrRpt2 by RPS2 through RIN4 (top-right), microscopic view of callose deposition in an A. thaliana leaf (bottom left), an example of no hypersensitive response (HR), top, and HR in A. thaliana leaves (bottom right)]] The use of A. thaliana has led to many breakthroughs in the advancement of knowledge of how plants manifest plant disease resistance. The reason most plants are resistant to most pathogens is through nonhost resistance - not all pathogens will infect all plants. An example where A. thaliana was used to determine the genes responsible for nonhost resistance is Blumeria graminis, the causal agent of powdery mildew of grasses. A. thaliana mutants were developed using the mutagen ethyl methanesulfonate and screened to identify mutants with increased infection by B. graminis. The mutants with higher infection rates are referred to as PEN mutants due to the ability of B. graminis to penetrate A. thaliana to begin the disease process. The PEN genes were later mapped to identify the genes responsible for nonhost resistance to B. graminis. In general, when a plant is exposed to a pathogen, or nonpathogenic microbe, an initial response, known as PAMP-triggered immunity (PTI), occurs because the plant detects