Rice allelochemical momilactone B inhibits Arabidopsis by disturbing ABA and auxin signaling pathways

Authors: WU, JIANXIN - Fujian Agricultural & Forestry University; LONG, JUN - Fujian Agricultural & Forestry University; LIN, XIANHUI - Fujian Agricultural & Forestry University; CHANG, ZHENYI - Fujian Agricultural & Forestry University; Baerson, Scott; DING, GHAOHUI - Fujian Agricultural & Forestry University; WU, XIAOYAN - Fujian Agricultural & Forestry University; Pan, Zhiqiang - Peter; SONG, YUANYUAN - Fujian Agricultural & Forestry University; ZENG, RENSEN - Fujian Agricultural & Forestry University

Submitted to: bioRxiv
Publication Type: Other
Publication Acceptance Date: 10/1/2020
Publication Date: 10/1/2020
Citation: Wu, J., Long, J., Lin, X., Chang, Z., Baerson, S.R., Ding, G., Wu, X., Pan, Z., Song, Y., Zeng, R. 2020. Rice allelochemical momilactone B inhibits Arabidopsis by disturbing ABA and auxin signaling pathways. bioRxiv. https://doi.org/10.1101/2020.09.30.320655.
DOI: https://doi.org/10.1101/2020.09.30.320655

Interpretive Summary: Many rice varieties possess allelopathy activity, a chemical interaction between plants mediated by the release of bioactive metabolites known as allelochemicals. This allelopathic potential can play an important role in weed control. Momilactones, a subgroup of bioactive metabolites in rice plants, were identified and isolated from root exudates of allelopathic rice varieties in 2000’s. These compounds are thought to contribute to allelopathic interactions between plants. In this report, the model plant Arabidopsis was used to study the allelopathic mechanism of momilactones, specifically momilactone B (MB). Our results showed that MB exhibits pleiotropic allelopathic effects on seed germination, seedlings establishment and root growth of Arabidopsis. It represses seed germination by activating abscisic acid biosynthesis and signaling. Furthermore, MB inhibits root growth mainly by altering auxin biosynthesis and regulating polar auxin transport in the root tips. The application of exogenous auxin partially recovered the MB-induced root growth arrest. Our findings highlight the critical roles of abscisic acid and auxin in MB-mediated allelopathic inhibition.

Technical Abstract: Momilactone B (MB) is a key allelochemical released from rice (Oryza sativa). However, the mode of action of MB remains elusive. In this study, we used a model plant Arabidopsis (Arabidopsis thaliana) to investigate the inhibitory mechanisms of MB on seed germination, seedling establishment and root growth using real-time Polymerase Chain Reaction (PCR) and confocal microscope. Our results showed that the transcription levels of the key abscisic acid (ABA) biosynthetic and signaling genes, particularly the transcription factor ABA-Insensitive (ABI) 4, were dramatically increased in response to MB; however, ABI4-deficient mutant of Arabidopsis showed less susceptible to MB and rice root exudates. Although the expression of DELLA genes (encoding proteins containing a motif with five amino acids: aspartate-glutamate-leucine-leucine-alanine or D-E-L-L-A in the single letter amino acid code), the key negative regulators in gibberellin (GA) signaling, was significantly induced in the presence of momilactone B, exogenous GA did not release MB-inhibited seed germination and seedling development. Moreover, MB exposure led to the reduction of the maintenance of root meristem associated with the reduction of auxin concentration, downregulation of auxin biosynthesis genes, and efflux transporters in MB-treated root tips. Exogenous auxin, however, recovered the MB-induced root growth arrest. These results suggest that MB may suppress seed germination and root growth mainly by disturbing the ABA and auxin signaling. These findings highlight the crucial roles of plant phytohormones in responses to allelochemicals.