Ethylene-independent functions of the ethylene precursor ACC in Marchantia polymorpha


The plant hormone ethylene has many roles in growth and development1. In seed plants, the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) is converted into ethylene by ACC oxidase (ACO), and treatment with ACC induces ethylene responses2. However, non-seed plants lack ACO homologues3,4,5,6,7,8, which led us to examine the relationship between ACC and ethylene in the liverwort Marchantia polymorpha. Here, we demonstrate that ACC and ethylene can induce divergent growth responses in Marchantia. Ethylene increases plant and gemma size, induces more gemma cups and promotes gemmae dormancy. As predicted, Mpctr1-knockout mutants display constitutive ethylene responses, whereas Mpein3-knockout mutants exhibit ethylene insensitivity. Compared with the wild type, Mpctr1 gemmae have more and larger epidermal cells, whereas Mpein3 gemmae have fewer and smaller epidermal cells, suggesting that ethylene promotes cell division and growth in developing gemmae. By contrast, ACC treatment inhibits gemma growth and development by suppressing cell division, even in the Mpein3-knockout alleles. Knockout mutants of one or both ACC SYNTHASE (ACS) gene homologues produce negligible levels of ACC, have more and larger gemma cups, and have more-expanded thallus branches. Mpacs2 and Mpacs1 Mpacs2 gemmae also display a high frequency of abnormal apical notches (meristems) that are not observed in ethylene mutants. These findings reveal that ethylene and ACC have distinct functions, and suggest that ACC is a signalling molecule in Marchantia. ACC may be an evolutionarily conserved signal that predates its efficient conversion to ethylene in higher plants.

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Fig. 1: Ethylene treatment enhances thallus growth and gemma size, induces gemma cups and reduces gemma non-dormancy in WT Marchantia.
Fig. 2: Mpctr1- and Mpein3-knockout mutants display constitutive ethylene responses and ethylene insensitivity, respectively.
Fig. 3: ACC treatment inhibits plant growth and reduces gemma epidermal cell number.
Fig. 4: Single and double Mpacs1- and Mpacs2-knockout mutants have reduced ACC levels, abnormal thallus shape, increased gemma non-dormancy and apical notch defects.

Data availability

The data that support the findings of this study are available from the corresponding authors on reasonable request. Publicly available RNA-seq libraries analysed in this study are listed in Supplementary Data 2. The nucleotide and/or protein sequences analysed in this study are publicly available from NCBI SRA (, NCBI Landmark Database (, Phytozome (, GenBank (, MarpolBase (, Congenie ( and refs. 10,46,47,48,49,50,51,52.


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We thank Y.-T. Kao for help with maintaining plants; M. Tucker for 1-MCP; and H. Sze for use of her microscope. We acknowledge the Imaging Core Facility in the department of Cell Biology and Molecular Genetics at the University of Maryland, College Park, for the Leica SP5X Laser Scanning Confocal microscope. This work was supported by a NSF grant (no. MCB-1714993, to C.C.), the Australian Research Council (DP170100049, to J.L.B.) and a China Scholarship Council graduate student fellowship (to D.L.). U.A. was supported in part by a grant to the University of Maryland from the Howard Hughes Medical Institute through the Science Education Program. C.C. was supported in part by the Maryland Agricultural Experiment Station.

Author information




All of the authors were involved in aspects of the experimental design. C.C. and J.L.B. conceived and directed the project. D.L. performed almost all of the experiments and produced most of the figures. E.F.-S. generated most of the mutants and conducted in silico analysis of MpACS gene expression. A.C. and U.A. made initial discoveries and performed preliminary experiments. J.M.C. cloned MpACS1 and MpACS2 for yeast expression and generated the ACS tree. J.L.B. generated the CTR1 and EIN3 trees. C.C. wrote the paper with contributions from J.L.B., D.L. and E.F.-S. All of the authors reviewed and commented on the manuscript.

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Correspondence to John L. Bowman or Caren Chang.

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Supplementary Information

Supplementary Figs. 1–14, Data 1, Methods 1 and 2, Table 1 and References.

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Supplementary Data 2

MpACS1 and MpACS2 expression data from publicly available RNA-seq libraries (source data for Supplementary Fig. 10).

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Li, D., Flores-Sandoval, E., Ahtesham, U. et al. Ethylene-independent functions of the ethylene precursor ACC in Marchantia polymorpha. Nat. Plants 6, 1335–1344 (2020).

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