Nitrate enhances the secondary growth of storage roots in Panax ginseng

Kyoung Rok Geem; Jaewook Kim; Wonsil Bae; Moo-Geun Jee; Jin Yu; Inbae Jang; Dong-Yun Lee; Chang Pyo Hong; Donghwan Shim; Hojin Ryu

doi:10.1016/j.jgr.2022.05.009

Nitrate enhances the secondary growth of storage roots in Panax ginseng

J Ginseng Res. 2023 May;47(3):469-478. doi: 10.1016/j.jgr.2022.05.009. Epub 2022 Jun 2.

Authors

Kyoung Rok Geem¹, Jaewook Kim², Wonsil Bae¹, Moo-Geun Jee³, Jin Yu⁴, Inbae Jang⁴, Dong-Yun Lee⁵, Chang Pyo Hong⁶, Donghwan Shim², Hojin Ryu^{1

7}

Affiliations

¹ Department of Biology, Chungbuk National University, Cheongju, Republic of Korea.
² Department of Biological Sciences, Chungnam National University, Daejeon, Republic of Korea.
³ Ginseng & Medicinal Plant Research Institute, Chungnam Agricultural Research & Extention Service, Keumsan, Republic of Korea.
⁴ Department of Herbal Crop Research, National Institute of Horticultural and Herbal Science, Rural Development Administration, Eumseong, Republic of Korea.
⁵ Korea Ginseng Corporation, R&D Headquarters, Daejeon, Republic of Korea.
⁶ Theragen Bio Co., Ltd, Suwon, Republic of Korea.
⁷ Department of Biological Sciences and Biotechnology, Chungbuk National University, Cheongju, Republic of Korea.

Abstract

Background: Nitrogen (N) is an essential macronutrient for plant growth and development. To support agricultural production and enhance crop yield, two major N sources, nitrate and ammonium, are applied as fertilizers to the soil. Although many studies have been conducted on N uptake and signal transduction, the molecular genetic mechanisms of N-mediated physiological roles, such as the secondary growth of storage roots, remain largely unknown.

Methods: One-year-old P. ginseng seedlings treated with KNO₃ were analyzed for the secondary growth of storage roots. The histological paraffin sections were subjected to bright and polarized light microscopic analysis. Genome-wide RNA-seq and network analysis were carried out to dissect the molecular mechanism of nitrate-mediated promotion of ginseng storage root thickening.

Results: Here, we report the positive effects of nitrate on storage root secondary growth in Panax ginseng. Exogenous nitrate supply to ginseng seedlings significantly increased the root secondary growth. Histological analysis indicated that the enhancement of root secondary growth could be attributed to the increase in cambium stem cell activity and the subsequent differentiation of cambium-derived storage parenchymal cells. RNA-seq and gene set enrichment analysis (GSEA) revealed that the formation of a transcriptional network comprising auxin, brassinosteroid (BR)-, ethylene-, and jasmonic acid (JA)-related genes mainly contributed to the secondary growth of ginseng storage roots. In addition, increased proliferation of cambium stem cells by a N-rich source inhibited the accumulation of starch granules in storage parenchymal cells.

Conclusion: Thus, through the integration of bioinformatic and histological tissue analyses, we demonstrate that nitrate assimilation and signaling pathways are integrated into key biological processes that promote the secondary growth of P. ginseng storage roots.

Keywords: Hormone; Nitrate; Panax ginseng; Root secondary growth.