Distinct metabolome changes during seed germination of lettuce (Lactuca sativa L.) in response to thermal stress as revealed by untargeted metabolomics analysis

Authors: WEI, SHIWEI - Shanghai Agrobiological Gene Center; YANG, XIAO - Chinese Academy Of Agricultural Sciences; HUO, GUOTAO - Shanghai Agrobiological Gene Center; GE, GUOJUN - Shanghai Agrobiological Gene Center; LIU, HONGYAN - Shanghai Agrobiological Gene Center; LUO, LIJUN - Shanghai Agrobiological Gene Center; Hu, Jinguo; HUANG, DANFENG - Beijing Jiaotong University; LONG, PING - Shanghai Agrobiological Gene Center

Submitted to: International Journal of Molecular Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/18/2020
Publication Date: 2/21/2020
Publication URL: https://handle.nal.usda.gov/10113/6937449
Citation: Wei, S., Yang, X., Huo, G., Ge, G., Liu, H., Luo, L., Hu, J., Huang, D., Long, P. 2020. Distinct metabolome changes during seed germination of lettuce (Lactuca sativa L.) in response to thermal stress as revealed by untargeted metabolomics analysis. International Journal of Molecular Sciences. 21(4):1481. https://doi.org/10.3390/ijms21041481.
DOI: https://doi.org/10.3390/ijms21041481

Interpretive Summary: The optimal temperature for lettuce seed germination ranges from 18 to 21 °C. At higher temperature, the germination is hampered or even inhibited known as thermoinhibition that limits the season and area for lettuce production. This study tested the germination of 304 lettuce accessions (255 from the USDA lettuce collection) under 21 °C, 28 °C and 35 °C, respectively, for 40 h. All accessions germinated very well under 21 °C; 129 accessions had more than 50% germination under 28 °C and, under 35 °C, one accession, PI 667844, had the highest germination percentage of 39.6%, and 189 accession did not germinate al all, 97 accessions had germination percentage ranging 0.1 to 4.9% and 17 accessions had germination percentage between 5% to 39.6%. An untargeted metabolomics approach was used to investigate the molecular basis of thermoinhibition by comparing the metabolites extracted from dry and germinated seeds of two genotypes that showed differences in germination at different temperatures. It was found that seeds of thermal-sensitive and thermal-tolerant accessions employed different metabolic strategies in response to thermal stress during germination. The accessions had high germination under 35 °C are useful for lettuce breeding programs to develop new cultivars suitable for extended summer production in temperate or tropical climates when soil temperatures are higher than the optimal germination temperature.

Technical Abstract: Temperature strongly influences lettuce (Lactuca sativa L.) seed germination. Different lettuce genotypes respond differently to higher temperatures or thermal stress. In this study, we evaluated the germination performance of 304 lettuce accessions incubated at three temperature settings, 21 °C, 28 °C and 35 °C, respectively, for 40 h. At 21 °C, seeds of all 304 accessions germinated very well with an average germination percentage of 87.72%; at 28 °C, the average germination percentage dropped to 42.84% and at 35 °C, the germination decreased to 1.01%. Then, we investigated changes in metabolic profiles of lettuce seed response to thermal stress using an untargeted metabolomics approach. Results suggested that seeds of thermal-sensitive and thermal-tolerant cultivars employed different metabolic strategies in response to thermal stress during germination. Thermal-sensitive buds accumulated more significant amounts of organic acids, amino acids, sugars, sterols, phenolic compounds and terpenoids compared to thermal-tolerant buds at 21 °C. Thermal-tolerant lettuce cultivar accumulated higher concentrations of amino acids, organic acids, sugars, sesquiterpene lactones, sterols, and fatty acids derivatives during the germination at 35 °C compared to germinated at 21 °C. This investigation paves the way to link the metabolomics to other external and internal factors affecting lettuce seed germination under thermal stress.