Plant hormones (Literature sources on phytohormones and plant signalling)

Authors: Tomoyuki Koyama, Honami Zaizen, Ikuo Takahashi, Hidemitsu Nakamura, Masatoshi Nakajima and Tadao Asami.

International Journal of Molecular Sciences (2023)

Abstract: "Ethylene is the only gaseous plant hormone that regulates several aspects of plant growth, from seedling morphogenesis to fruit ripening and organ senescence. Ethylene also stimulates the germination of Striga hermonthica, a root parasitic weed that severely damages crops in sub-Saharan Africa. Thus, ethylene response stimulants can be used as weed and crop control agents. Ethylene and ethephon, an ethylene-releasing compound, are currently used as ethylene response inducers. However, since ethylene is a gas, which limits its practical application, we targeted the development of a solid ethylene response inducer that could overcome this disadvantage. We performed chemical screening using Arabidopsis thaliana “triple response” as an indicator of ethylene response. After screening, we selected a compound with a thiourea skeleton and named it ZKT1. We then synthesized various derivatives of ZKT1 and evaluated their ethylene-like activities in Arabidopsis. Some derivatives showed considerably higher activity than ZKT1, and their activity was comparable to that of 1-aminocyclopropane-1-carboxylate. Mode of action analysis using chemical inhibitors and ethylene signaling mutants revealed that ZKT1 derivatives activate the ethylene signaling pathway through interactions with its upstream components. These thiourea derivatives can potentially be potent crop-controlling chemicals."

Authors: Xiaofang Li, Pingping Fang, Mingxuan Li and Pei Xu.

In Vitro Cellular & Developmental Biology - Plant (2023)

Abstract: "Structural analogs of enzyme substrates involved in plant hormone biosynthesis can either inhibit or enhance hormone-related responses depending on their specific chemical characteristics. Ethylene is an important gaseous phytohormone regulating a myriad of physiological and developmental processes. The substrate of the ethylene biosynthesis key enzyme ACC oxidase (ACO), 1-aminocyclopropane-1-carboxylate acid (ACC), is the direct precursor of ethylene. Previous studies have identified a series of ACC analogs as ethylene antagonists competitively binding with ACO. Here, this study identified methyl 1-aminocyclopropanecarboxylate (methyl-ACC), a structural analog of ACC, as an agonist of ethylene response in plants. Methyl-ACC triggered enhanced ethylene-related responses in plants similar to the effects of ACC, such as restrained root elongation, increased root hair number, promoted dark-induced leaf senescence, and accelerated ripening of postharvest tomato fruit. A higher amount of ethylene release was detected from the tomato leaves treated with methyl-ACC than from the mock control. These bioactivities of methyl-ACC render it a potential plant growth regulator (PGR) for the agricultural and postharvest industries. RT-qPCR revealed a generally upregulated expression of the ethylene biosynthesis genes in detached tomato leaves under methyl-ACC treatment. In vivo and in vitro enzymatic activity analyses showed that methyl-ACC had no obvious effect on the total ACO activity in detached tomato leaves nor on the activity of recombinant SlACO1, the predominantly expressed ACO family member in this tissue. This study offers a promising new PGR and adds to the current knowledge on the structure–function-regulation relationship of compounds associated with ethylene biosynthesis. The mechanism by which methyl-ACC exerts its function is discussed."

Authors: Marlon Enrique López, Iasminy Silva Santos, Robert Marquez Gutiérrez, Andrea Jaramillo Mesa, Carlos Henrique Cardon, Juliana Maria Espíndola Lima, André Almeida Lima and Antonio Chalfun-Junior-

Frontiers in Plant Science (2022)

Abstract: "Coffee (Coffea arabica L.) presents an asynchronous flowering regulated by an endogenous and environmental stimulus, and anthesis occurs once plants are rehydrated after a period of water deficit. We evaluated the evolution of Abscisic Acid (ABA), ethylene, 1-aminocyclopropane-1-carboxylate (ACC) content, ACC oxidase (ACO) activity, and expression analysis of the Lysine Histidine Transporter 1 (LHT1) transporter, in the roots, leaves, and flower buds from three coffee genotypes (C. arabica L. cv Oeiras, Acauã, and Semperflorens) cultivated under field conditions with two experiments. In a third field experiment, the effect of the exogenous supply of ACC in coffee anthesis was evaluated. We found an increased ACC level, low ACO activity, decreased level of ethylene, and a decreased level of ABA in all tissues from the three coffee genotypes in the re-watering period just before anthesis, and a high expression of the LHT1 in flower buds and leaves. The ethylene content and ACO activity decreased from rainy to dry period whereas the ABA content increased. A higher number of opened and G6 stage flower buds were observed in the treatment with exogenous ACC. The results showed that the interaction of ABA-ACO-ethylene and intercellular ACC transport among the leaves, buds, and roots in coffee favors an increased level of ACC that is most likely, involved as a modulator in coffee anthesis. This study provides evidence that ACC can play an important role independently of ethylene in the anthesis process in a perennial crop."

Authors: Elisa Gamalero, Guido Lingua and Bernard R. Glick.  

Biology (2023)

Abstract: "Here, a brief summary of the biosynthesis of 1-aminocyclopropane-1-carboxylate (ACC) and ethylene in plants, as well as overviews of how ACC and ethylene act as signaling molecules in plants, is presented. Next, how the bacterial enzyme ACC deaminase cleaves plant-produced ACC and thereby decreases or prevents the ethylene or ACC modulation of plant gene expression is considered. A detailed model of ACC deaminase functioning, including the role of indoleacetic acid (IAA), is presented. Given that ACC is a signaling molecule under some circumstances, this suggests that ACC, which appears to have evolved prior to ethylene, may have been a major signaling molecule in primitive plants prior to the evolution of ethylene and ethylene signaling. Due to their involvement in stimulating ethylene production, the role of D-amino acids in plants is then considered. The enzyme D-cysteine desulfhydrase, which is structurally very similar to ACC deaminase, is briefly discussed and the possibility that ACC deaminase arose as a variant of D-cysteine desulfhydrase is suggested."

Authors: Toshiki Uji and Hiroyuki Mizuta.

Frontiers in Plant Science (2022)

Abstract: "Seaweeds or macroalgae are important primary producers that serve as a habitat for functioning ecosystems. A sustainable production of macroalgae has been maintained by a diverse range of life cycles. Reproduction is the most dynamic change to occur during its life cycle, and it is a key developmental event to ensure the species’ survival. There is gradually accumulating evidence that plant hormones, such as abscisic acid and auxin, have a role on the sporogenesis of brown alga (Saccharina japonica). Recent studies reported that 1-aminocylopropane-1-carboxylic acid, an ethylene precursor, regulates sexual reproduction in red alga (Neopyropia yezoensis) independently from ethylene. In addition, these macroalgae have an enhanced tolerance against abiotic and biotic stresses during reproduction to protect their gametes and spores. Herein, we reviewed the current understanding on the regulatory mechanisms of red and brown algae on their transition from vegetative to reproductive phase."

Authors: L. Vanderstraeten, R. Sanchez-Muñoz, T. Depaepe, F. Auwelaert and D. Van Der Straeten.

Plant Methods (2022)

Abstract: "Background - Grafting is a technique widely used in horticulture that also has been applied in agriculture. In plant physiology, grafting facilitates the elucidation of mechanisms underlying growth and developmental processes, through the construction of chimeric plants with organs of different genotypes. Despite its small size, the model species Arabidopsis thaliana is very amenable for grafting, which can be useful to investigate transport of nutrients, amino acids or secondary metabolites between different tissues, or to investigate developmental processes depending on root-to-shoot communication, such as shoot branching, root and shoot plasticity upon shade avoidance, or disease resistance. Nevertheless, grafting protocols are usually technically challenging and training is required to achieve a reasonable success rate. Additionally, specialized tools and equipment are often needed, such as chips to accommodate the grafted plantlets or collars to maintain the contact between root and shoot. Results - In this methodology paper, we provide a fast, easy, accessible, and specialized equipment-free protocol that enables high success ratios. Critical steps and notes are detailed, easing the implementation of the procedure for non-trained researchers. An example of the protocol application by three independent non-trained researchers shows that this method allows to achieve a 90–100% of grafting efficiency after 6 days post-grafting recovery. In addition, the grafting of Col-0 with the acs8x mutant, depleted in 1-aminocyclopropane-1-carboxylic acid (ACC), the biosynthetic precursor of the phytohormone ethylene, provides an example of the application of this optimized protocol, showing the suitability of the process to study long-distance transport processes. Conclusions - We present an optimized protocol for hypocotyl grafting of 4-day-old Arabidopsis thaliana seedlings. The combination of conditions yields a grafting success of 90–100% and provides an easy and accessible methodology, reducing the time frame, and without the necessity of acquiring specialized equipment. The presented protocol is simple, fast and highly efficient, easing the inclusion of hypocotyl grafting assays in any research project. In addition, the description of the protocol is detailed to a level ensuring that even non-trained researchers, are sufficiently prepared to adopt the grafting methodology."