The plant hormone ethylene promotes abiotic stress tolerance in the liverwort Marchantia polymorpha

Ethylene Signaling Modulates Dehydrin Expression in Arabidopsis thaliana Under Prolonged Dehydration

Dehydrins are stress-inducible proteins with protective functions, characterized by high hydrophilicity, thermostability, and a low degree of secondary structure. They stabilize cellular membranes, preserve macromolecule conformation, and support enzymatic and structural protein functions. Their accumulation in plant tissues under drought is regulated by abscisic acid (ABA)-dependent and ABA-independent pathways. Ethylene plays a key role in stress adaptation, but its relationship with dehydrin accumulation remains unclear. This study investigates how ethylene influences dehydrin expression in Arabidopsis thaliana during prolonged dehydration using transcript profiling and immunodetection in wild-type (Col-0), ethylene-constitutive (ctr1-1), and ethylene-insensitive (ein3eil1) mutants. Comparative analyses showed increased survival of ctr1-1 plants under dehydration stress, likely due to reduced oxidative damage. Analysis of dehydrin-coding genes identified multiple Ethylene Response Factor (ERF) binding sites, flanking the transcription start sites, which suggests a fine-tuned ethylene-dependent regulation. The ability of ethylene signaling to either suppress or stabilize particular dehydrins was demonstrated by RT-qPCR and immunodetection experiments. Under drought stress, ethylene signaling appeared to suppress root-specific dehydrins. A Y-segment-containing protein with approximate molecular weight of 20 kDa showed decreased levels in ctr1-1 and higher accumulation in ein3eil1, indicating that ethylene signaling acts as a negative regulator. These results provide new information on the dual role of ethylene in dehydrin control, highlighting its function as a molecular switch in stress adaptive responses.

The NbCBP1-NbSAMS1 Module Promotes Ethylene Accumulation to Enhance Nicotiana benthamiana Resistance to Phytophthora parasitica Under High Potassium Status

Potassium (K) fertilization is crucial for plant resistance to pathogens, but the underlying mechanisms remain unclear. Here, we investigate the molecular mechanism by which the addition of K promotes resistance in Nicotiana benthamiana to Phytophthora parasitica. We found that N. benthamiana with high K content (HK, 52.3 g/kg) produced more ethylene in response to P. parasitica infection, compared to N. benthamiana with low-K content (LK, 22.4 g/kg). An exogenous ethylene application effectively increased resistance in LK N. benthamiana to the level under HK status, demonstrating the involvement of ethylene in the HK-associated resistance in N. benthamiana. Further, transcriptome analysis showed that NbSAMS1, encoding ethylene biosynthesis, was induced to upregulate P. parasitica about five times higher in HK than in LK N. benthamiana. NbSAMS1 overexpression enhanced resistance in LK plants, whereas NbSAMS1 silencing reduced resistance in HK plants, confirming its importance in conferring resistance. Furthermore, we identified a calcium-binding protein, NbCBP1, which interacted with NbSAMS1, promoting its expression in HK N. benthamiana. Silencing NbCBP1 compromised resistance in HK N. benthamiana, whereas its overexpression improved resistance in LK N. benthamiana. Notably, NbCBP1 protected NbSAMS1 from degradation by the 26S proteasome, thereby sustaining ethylene accumulation in HK N. benthamiana in response to P. parasitica infection. Thus, our research elucidated some mechanisms of the NbCBP1-NbSAMS1 module associated with disease resistance in HK N. benthamiana.

Identification and characterization of DICER-LIKE genes and their roles in Marchantia polymorpha development and salt stress response

DICER-LIKE (DCL) proteins play a central role in plant small RNA (sRNA) biogenesis. The genome of the early land plant Marchantia polymorpha encodes four DCL proteins: MpDCL1a, MpDCL1b, MpDCL3, and MpDCL4. While MpDCL1a, MpDCL3 and MpDCL4 show high similarities to their orthologs in Physcomitrium patens and Arabidopsis thaliana, MpDCL1b shares only a limited homology with PpDCL1b, but it is very similar, in terms of functional domains, to orthologs in other moss and fern species. We generated Mpdclge mutant lines for all MpDCL genes with the CRISPR/Cas9 system and conducted phenotypic analyses under control, salt stress, and phytohormone treatments to uncover specific MpDCL functions. The mutants displayed severe developmental aberrations, altered responses to salt and phytohormones, and disturbed sexual organ development. By combining mRNA and sRNA analyses, we demonstrate that MpDCLs and their associated sRNAs play pivotal roles in regulating development, abiotic stress tolerance and phytohormone response in M. polymorpha. We identified MpDCL1a in microRNA biogenesis, MpDCL4 in trans-acting small interfering RNA generation, and MpDCL3 in the regulation of pathogen-related genes. Notably, salt sensitivity in M. polymorpha is dependent on MpDCL1b and Mpdcl1bge mutants display enhanced tolerance and reduced miRNA expression in response to salt stress. We propose that M. polymorpha employs specific mechanisms for regulating MpDCL1b associated miRNAs under high salinity conditions, potentially shared with other species harboring MpDCL1b homologs.

Environmental Pollutant Anthracene Induces ABA-Dependent Transgenerational Effects on Gemmae Dormancy in Marchantia polymorpha

Anthracene, a polycyclic aromatic hydrocarbon (PAH) from fossil fuel combustion, poses significant environmental threats. This study investigates the role of abscisic acid (ABA) in the anthracene tolerance of the liverwort Marchantia polymorpha using mutants deficient in ABA perception (Mppyl1) or biosynthesis (Mpaba1). In this study, we monitored the role of ABA in the anthracene tolerance response by tracking two ABA-controlled traits: plant growth inhibition and gemmae dormancy. We found that the anthracene-induced inhibition of plant growth is dose-dependent, similar to the growth-inhibiting effect of ABA, but independent of ABA pathways. However, gemmae dormancy was differentially affected by anthracene in ABA-deficient mutants. We found that gemmae from anthracene-exposed WT plants exhibited reduced germination compared to those from mock-treated plants. This suggests that the anthracene exposure of mother plants induces a transgenerational effect, resulting in prolonged dormancy in their asexual propagules. While Mppyl1 gemmae retained a dormancy delay when derived from anthracene-exposed thalli, the ABA biosynthesis mutant Mpaba1 did not display any significant dormancy delay as a consequence of anthracene exposure. These results, together with the strong induction of ABA marker genes upon anthracene treatment, imply that anthracene-induced germination inhibition relies on ABA synthesis in the mother plant, highlighting the critical role of MpABA1 in the tolerance response. These findings reveal a complex interplay between anthracene stress and ABA signaling, where anthracene triggers ABA-mediated responses, influencing reproductive success and highlighting the potential for leveraging genetic and hormonal pathways to enhance plant resilience in contaminated habitats.

Evolution of ethylene as an abiotic stress hormone in streptophytes

All land plants modulate their growth and physiology through intricate signaling cascades. The majority of these are at least modulated-and often triggered-by phytohormones. Over the past decade, it has become apparent that some phytohormones have an evolutionary origin that runs deeper than plant terrestrialization-many emerged in the streptophyte algal progenitors of land plants. Ethylene is such a case. Here we synthesize the current knowledge on the evolution of the phytohormone ethylene and speculate about its deeply conserved role in adjusting stress responses of streptophytes for more than half a billion years of evolution.

Loss of ACO4 in petunia improves abiotic stress tolerance by reducing the deleterious effects of stress-induced ethylene

To investigate the role of ethylene (ET) in abiotic stress tolerance in petunia cv. 'Mirage Rose', petunia plants in which the ET biosynthesis gene 1-aminocyclopropane-1-carboxylic acid oxidase 4 (ACO4) was knocked out (phaco4 mutants) and wild-type (WT) plants were exposed to heat and drought conditions. Loss of function of ACO4 significantly delayed leaf senescence and chlorosis under heat and drought stress by maintaining the SPAD values and the relative water content, indicating a greater stress tolerance of phaco4 mutants than that of WT plants. This tolerance was related to the lower ET and reactive oxygen species levels in the mutants than in WT plants. Furthermore, the stress-induced expression of genes related to ET signal transduction, antioxidant and proline activities, heat response, and biosynthesis of abscisic acid was higher in the mutants than in WT plants, indicating a greater stress tolerance in the former than in the latter. These results demonstrate the deleterious effects of stress-induced ET on plant growth and provide a better physiological and molecular understanding of the role of stress ET in the abiotic stress response of petunia. Because the loss of function of ACO4 in petunia improved stress tolerance, we suggest that ACO4 plays a vital role in stress-induced leaf senescence and acts as a negative regulator of abiotic stress tolerance.

AtSAMS regulates floral organ development by DNA methylation and ethylene signaling pathway

S-adenosylmethionine synthase is the key enzyme involved in the biosynthesis of S-adenosylmethionine, which serves as the universal methyl group donor and a common precursor for the biosynthesis of ethylene and polyamines. However, little is known about how SAMS controls plant development. Here, we report that the abnormal floral organ development in the AtSAMS-overexpressing plants is caused by DNA demethylation and ethylene signaling. The whole-genome DNA methylation level decreased, and ethylene content increased in SAMOE. Wild-type plants treated with DNA methylation inhibitor mimicked the phenotypes and the ethylene levels in SAMOE, suggesting that DNA demethylation enhanced ethylene biosynthesis, which led to abnormal floral organ development. DNA demethylation and elevated ethylene resulted in changes in the expression of ABCE genes, which is essential for floral organ development. Furthermore, the transcript levels of ACE genes were highly correlated to their methylation levels, except for the down-regulation of the B gene, which might have resulted from demethylation-independent ethylene signaling. SAMS-mediated methylation and ethylene signaling might create crosstalk in the process of floral organ development. Together, we provide evidence that AtSAMS regulates floral organ development by DNA methylation and ethylene signaling pathway.