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

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.