Analysis of LEA protein family members in Lepidium apetalum seeds and the expression of LaLEA1 in seedlings in response to abiotic stresses

To study the biological function of late embryogenesis abundant (LEA) proteins in Lepidium apetalum Willd. , genes encoding LEA family proteins were identified from the seed transcriptome. The sequence most closely related to germination at a low temperature was selected and gene expressions in response to low temperature stress further studied. The results show that 27 LEA genes were expressed in seeds germinating at the low temperature: 3 genes were upregulated, 20 were downregulated, and 4 were not significantly different from controls. The most prominent of the upregulated genes, LaLEA1, contained an open reading frame of 624 bp and encoded 208 amino acids. The protein was rich in hydrophilic amino acids including threonine, alanine, glutamine, and lysine. It is predicted that the secondary structure contains α-helices and irregular curls. Real-time quantitative PCR results show that under low temperature stress, the expression of LaLEA1 was first downregulated and then upregulated rapidly, reaching its highest expression at 12 h, then the expression of LaLEA1 was reduced slightly but maintained higher than that of the non-stress group. As the expression of LaLEA1 was significantly altered in response to low temperature stress, we investigated the expression of LaLEA1 also in response to other abiotic stresses, i.e., salinity and drought. L. apetalum seedlings wilted in the early stage following NaCl or osmotic (polyethylene glycol) stresses, but recovered quickly, showing a strong tolerance. Real-time quantitative PCR results show that LaLEA1 was rapidly upregulated following salt and osmotic stresses, and its expression profile was closely related to NaCl or PEG concentrations. Expression was up to 7.9-fold higher than that of the control after 6 h of salt stress. These results suggest that L. apetalum seedlings responded quickly to salt stress. The response to osmotic stress was slightly slower; expression of LaLEA1 was 6.0-fold higher than that of the control after 12 h. Thus, LaLEA1 played an important role in abiotic stress tolerance. These results provide a basis for further analysis of the role of the LEA genes in the stress resistance of L. apetalum. Additional key words: gene expression, low temperature, osmotic stress, salinity. Submitted 27 September 2019, last revision 15 December 2019, accepted 19 December 2019. Abbreviations: LEA late embryogenesis abundant; PEG polyethylene glycol. Acknowledgments: This work was supported by grants from the “13th Five-Year” Plan for Key Discipline Biology, Xinjiang Normal University (17SDKD0201), the National Natural Science Foundation of China (31660079 and 31460041), and the Open projects of the Beijing Key Laboratory of Resistance Genes Resource and Molecular Development (2017GD03), Research and Innovation Project for Graduate Students in Xinjiang Uygur Autonomous Region. The first two authors contributed equally to this work. * Corresponding author; e-mail: 954843437@qq.com Introduction Lepidium apetalum Willd. (family Brassicaceae), which has medicinal and nutritional value, is distributed worldwide from 400 to 2 000 m above sea level. This plant has the ability to adapt to a widely differing environments producing different ecotypes. For example, the ecotype in northern Xinjiang (China) has been reported to grow at 0 to 5 °C in some cases (Mao and Zhang, 1994). The climate in the mountainous areas of northern Xinjiang is very dry with some snow in winter. In early spring, ephemeral plants germinate and grow rapidly in the cold soil, which is soaked with melted snow, completing their life cycles before the soil dries up. This harsh environment makes L. apetalum living in northern Xinjiang, China unique in its ability to tolerate cold early spring weather, and to germinate and grow under such conditions (Yang et al. 2015). In a study of seed germination characteristics, it was found that the low-temperature germination of L. apetalum proceeds as follows: at temperatures of 0 to