Compared with other crops, pennycress (Thlaspi arvense L.) is a niche emerging oil crop. In recent years, research on pennycress has been increasingly reflected in various directions. Pennycress belongs to the Brassicaceae family and was introduced from Eurasia to North America. It has been found worldwide as a cultivated plant and weed. In this paper, we review the advantages of pennycress as a supplementary model plant of Arabidopsis thaliana, oil and protein extraction technology, seed composition analysis based on metabolomics, germplasm resource development, growth, and ecological impact research, abiotic stress, fatty acid extraction optimization strategy, and other aspects of studies over recent years. The main research directions proposed for the future are as follows: (1) assemble the genome of pennycress to complete its entire genome data, (2) optimize the extraction process of pennycress as biodiesel, (3) analyze the molecular mechanism of the fatty acid synthesis pathway in pennycress, and (4) the functions of key genes corresponding to various adversity conditions of pennycress.

Pennycress (Thlaspi arvense L.), an annual herb of the mustard family Brassicacae, is native to Eurasia and now widely distributed throughout temperate North America. This species is currently being developed as a medicinal herb used to treat nephritis in China and an oilseed crop for biofuel production (Roque et al.2012). In November 2020, stunt and wilt symptoms were observed on above ground parts and swollen club-shaped galls were observed on the roots of T. arvense in most of the Chinese cabbage growing area in Kangding (30°03\'\"N,102°02\'\"E), Sichuan Province of China. The average disease incidence of swollen roots on T. arvense was 91.2% ( n=80). To identify the causal agent of this disease, the swollen roots of T. arvense were collected, crushed and observed under microscope (Fei et al.2017). Abundant resting spores were found in the root galls, which were spherical and 2.0 to 3.1 μm in diameter with an average length of 2.7 nm (n=100). The healthy roots and the root galls of T. arvense plants were further evaluated by PCR with P. brassicae-specific primers TC2F/TC2R (Cao et al. 2007). The results showed that a DNA fragment with an estimated size of 520 bp, as expected for that of P. brassicae, was consistently amplified in diseased roots, No PCR amplification occurred in the healthy roots with the TC2F/TC2R primers. Blast analysis of the 520 bp segment (GenBankMZ040496) showed the highest identity with the sequence of small subunit ribosomal RNA gene of P. brassicae (GenBankMH762161, 97.7%, E value=0). These results confirmed that the pathogen in the galled roots of T. arvense was P. brassicae. The pathogenicity of isolated P. brassicae was tested on both T. arvense and Chinese cabbage (B. campestris ssp. pekinensis). Resting spores were isolated from the diseased roots (Castlkbury et al. 1994) of T. arvense and suspended in Hoagland\'s solution to the final concentration of 1 × 107 spores per milliliter. Fifteen plastic pots (10 cm bottom diameter, 16 cm upper diameter, 13 cm high) were filled with soil (1 kg per pot) that was sterilized twice with high-temperature (121℃), high pressure (19 PSI) for 1.5 hours with a time interval of 2 days between. Inoculated pots received 100 mL spore suspension each. Fifteen control pots with sterilized field soil were treated with 100 mL Hoagland\'s solution each. Seeds of T. arvense and B. campestris were pre-germinated at 20°C on moist filter paper for 7 days and transplanted into the pots, five seedlings each and five pots per treatment. The pots were maintained in a greenhouse with 16 hours photoperiod at 24°C/16°C day/night temperature. After 7 weeks, plants in each pot were uprooted and the roots cleaned in running water and inspected for clubroot symptoms. Plants of T. arvense and Chinese cabbage in pots inoculated with resting spores showed clubroot symptoms while no disease symptoms were observed on any control plants. The disease incidence rate was 95.4% on T. arvense and 81.2% on B. campestris. Therefore, it was confirmed that P. brassicae could cause clubroot disease on T. arvense. To our knowledge, this is the first published report of clubroot disease on T. arvense in China. This finding is helpful for the management of clubroot on herbs and plants of biological origin in the cruciferous family.

Pennycress (Thlaspi arvense L.), a plant naturalized to North America, accumulates high levels of erucic acid in its seeds, which makes it a promising biodiesel and industrial crop. The main carbon sinks in pennycress embryos were found to be proteins, fatty acids, and cell wall, which respectively represented 38.5, 33.2, and 27.0% of the biomass at 21 days after pollination. Erucic acid reached a maximum of 36% of the total fatty acids. Together these results indicate that total oil and erucic acid contents could be increased to boost the economic competitiveness of this crop. Understanding the biochemical basis of oil synthesis in pennycress embryos is therefore timely and relevant to guide future breeding and/or metabolic engineering efforts. For this purpose, a combination of metabolomics approaches was conducted to assess the active biochemical pathways during oil synthesis. First, gas chromatography-mass spectrometry (GC-MS) profiling of intracellular metabolites highlighted three main families of compounds: organic acids, amino acids, and sugars/sugar alcohols. Secondly, these intermediates were quantified in developing pennycress embryos by liquid chromatography-tandem mass spectrometry (LC-MS/MS) in multiple reaction monitoring mode. Finally, partitional clustering analysis grouped the intracellular metabolites that shared a similar pattern of accumulation over time into eight clusters. This study underlined that: (i) sucrose might be stored rather than cleaved into hexoses; (ii) glucose and glutamine would be the main sources of carbon and nitrogen, respectively; and (iii) glycolysis, the oxidative pentose phosphate pathway, the tricarboxylic acid cycle, and the Calvin cycle were active in developing pennycress embryos.