The chrysanthemum DEAD-box RNA helicase, CmRH56, regulates rhizome outgrowth in response to drought stress

Authors: ZHANG, LILI - China Agriculture University; XU, YANJIE - China Agriculture University; LIU, XUENING - China Agriculture University; QIN, MEIZHU - China Agriculture University; LI, SHENGLAN - China Agriculture University; JIANG, TIANHUA - China Agriculture University; YANG, YINGJIE - China Agriculture University; Jiang, Cai-Zhong; GAO, JUNPING - China Agriculture University; HONG, BO - China Agriculture University; MA, CHAO - China Agriculture University

Submitted to: Journal of Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/20/2022
Publication Date: 5/20/2022
Citation: Zhang, L., Xu, Y., Liu, X., Qin, M., Li, S., Jiang, T., Yang, Y., Jiang, C., Gao, J., Hong, B., Ma, C. 2022. The chrysanthemum DEAD-box RNA helicase, CmRH56, regulates rhizome outgrowth in response to drought stress. Journal of Experimental Botany. 73(16):5671-5681. https://doi.org/10.1093/jxb/erac213.
DOI: https://doi.org/10.1093/jxb/erac213

Interpretive Summary: Many plants have evolved modified organs to perform special functions in response to certain environmental conditions. Rhizome is modified stem that consists of leaves, stems or internodes, and nodes, and grow horizontally under the surface of soil. Rhizome contains meristematic tissue capable of daughter plant, which is a unique feature distinct from other parts of plant, such as leaf, root, and lateral shoot. Rhizome as a plant propagation strategy and storage organ supports plant growth under stressful environments, and enables plant to perennate and survive from stress damage. It has been known that rhizome growth is an induced response to dramatic changes in surrounding environment. Rhizome growth can slow down significantly, and can even be inhibited completely until more favorable conditions are restored. However, mechanisms regulating rhizome growth under harsh environments are largely unknown. RNA helicases are ubiquitous enzymes in prokaryotes and eukaryotes, and function in RNA metabolism. Over the past decades, increasing evidences demonstrate that DEAD-box RNA helicases in plants are associated with a variety of cellular functions, developmental regulation and abiotic stress response. Moreover, it has been reported that several DEAD-box RNA helicases regulate plant development and respond to abiotic stresses through modulation of phytohormone pathways such as gibberellin (GA), auxin, abscisic acid (ABA). GA controls diverse aspects of plant growth and development, such as seed germination, stem elongation and leaf expansion. Previous studies suggest that GA may participate in rhizome development. For example, several genes related to GA pathway exhibited higher expression in rhizomes compared to regular stems in such as lotus (Nelumbo nucifera), bamboo (Phyllostachys praecox), and Oryza longistaminata. In Festuca arundinacea, several genes related to GA pathway were significantly reduced in rhizome under drought stress, suggesting drought-inhibited rhizome growth may also be regulated by GA pathway. However, the mechanisms that regulate GA pathway to modulate rhizome growth have not been fully characterized. Chrysanthemum (Chrysanthemum morifolium) is an herbaceous perennial plant and commercially important ornamental plant worldwide. Rhizome is the main organ for propagation and perennation in chrysanthemum. Abiotic stresses, such as low temperature and drought, can be major impediments to growth of rhizome in chrysanthemum. However, the regulatory mechanism governing rhizome growth in response to abiotic stresses such as severe drought stress remains to be elucidated. In this study, we identified a DEAD-box RNA helicase gene CmRH56 in chrysanthemum involved in rhizome outgrowth in response to drought stress. We found that CmRH56 in perennial herb chrysanthemum (Chrysanthemum morifolium) is specific expressed in rhizome shoot apex. Knockdown of CmRH56 expression reduces the number of rhizomes, and enhances the drought stress tolerance in chrysanthemum. CmRH56 modulates the expression of gibberellin (GA) catabolism gene CmGA2ox6 that regulates the deactivation of bioactive GAs. Exogenous GA treatment and silencing of CmGA2ox6 in chrysanthemum show more rhizome. These results demonstrate that the CmRH56 is a key player in modulating rhizome outgrowth under drought stress by influencing GA biosynthesis in chrysanthemum.

Technical Abstract: Plants have evolved complex mechanisms to reprogram growth in response to drought stress. Rhizome is a highly desirable organ for survival of drought stress, and regeneration ability of post-stress recovery in herbaceous perennial plant species. However, mechanisms regulating rhizome growth in perennial herbs during drought stress are unknown. Here, using reverse genetics, molecular and biochemical techniques, we identified a DEAD-box RNA helicase gene CmRH56 in chrysanthemum involved in rhizome outgrowth in response to drought stress. We found that CmRH56 in perennial herb chrysanthemum (Chrysanthemum morifolium) is specific expressed in rhizome shoot apex. Knockdown of CmRH56 expression reduces the number of rhizomes, and enhances the drought stress tolerance in chrysanthemum. CmRH56 modulates the expression of gibberellin (GA) catabolism gene CmGA2ox6 that regulates the deactivation of bioactive GAs. Exogenous GA treatment and silencing of CmGA2ox6 in chrysanthemum show more rhizome. These results demonstrate that the CmRH56 is a key player in modulating rhizome outgrowth under drought stress by influencing GA biosynthesis in chrysanthemum.