Nanoscale Iron trioxide catalyzes the synthesis of auxins analogs in artificial humic acids to enhance rice growth

Humic acids (HAs), kinds of valuable active carbon, are critical for improving soil fertility. However, the majority of soils are poor in HAs, arousing the development of artificial HAs. In this study, two iron-based catalysts (nanoscale iron trioxide (nFe₂O₃) and FeCl₃) were used to catalyze the hydrothermal humification of waste corn straw. With the help of ultra-performance liquid chromatography-mass spectrometry, we proposed the specific humification process with the action of catalysis for the first time, which is of great significance for the design, synthesis and application of artificial HAs in the future. Moreover, the growth-promoting effect and mechanisms of the artificial HAs were determined by rice planting in a greenhouse. Results showed that compared to no catalyst treatment, the FeCl₃ and nFe₂O₃ catalysts increased the decomposition rate of macromolecular biomass by 39 and 14 %, respectively, increasing the yield of artificial HAs. During the humification process, nFe₂O₃ catalysts benefit the formation of many aromatic structure monomers including furfural and hydroxycaproic acids. These monomers were condensed into growth hormone analogs such as vanillin and methionine sulfoxide and were further built in the artificial HAs. Therefore, the artificial HAs from nFe₂O₃ catalytic treatment promoted the rice growth the best, showing that the resultant germination rate, root activity, and photosynthetic rate of rice increased by 50, 167, and 72 %, respectively; moreover, the uptake and accumulation of water and nutrient by roots as well as the contents of soluble protein and sugar of rice are also significantly increased. This could be ascribed to the upregulated expression of functional genes including OsRHL1, OsZPT5-07, OsSHR2 and OsDCL. Considering both the economic and environmental benefits, we suggested that the artificial HAs, especially that produced with the action of nFe₂O₃ catalysis, are promising in alleviating environmental stress from waste biomass and sustainably improving agricultural production.

Tailored biosynthesis of gibberellin plant hormones in yeast

The application of small amounts of natural plant growth hormones, such as gibberellins (GAs), can increase the productivity and quality of many vegetable and fruit crops. However, gibberellin growth hormones usage is limited by the high cost of their production, which is currently based on fermentation of a natural fungal producer Fusarium fujikuroi that produces a mix of several GAs. We explored the potential of the oleaginous yeast Yarrowia lipolytica to produce specific profiles of GAs. Firstly, the production of the GA-precursor ent-kaurenoic acid (KA) at 3.75 mg/L was achieved by expression of biosynthetic enzymes from the plant Arabidopsis thaliana and upregulation of the mevalonate (MVA) pathway.

We then built a GA₄-producing strain by extending the GA-biosynthetic pathway and upregulating the MVA-pathway further, resulting in 17.29 mg/L GA₄. Additional expression of the F. fujikoroi GA-biosynthetic enzymes resulted in the production of GA₇ (trace amounts) and GA₃ (2.93 mg/L). Lastly, through protein engineering and the expression of additional KA-biosynthetic genes, we increased the GA₃-production 4.4-fold resulting in 12.81 mg/L. The developed system presents a promising resource for the recombinant production of specific gibberellins, identifying bottlenecks in GA biosynthesis, and discovering new GA biosynthetic genes.

Classification

Biological Sciences, Applied Biological Sciences.

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A complete biosynthetic pathway towards gibberellins was reconstructed in a microbial host

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The pathway towards ent-kaurenoic acid consisted of Arabidopsis thaliana enzymes

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The pathway from ent-kaurenoic acid to gibberellins GA₃, GA₄ and GA₇ consisted of Fusarium fujikuroi enzymes

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Y. lipolytica expressed 14 heterologous genes for gibberellins biosynthesis and had 5 genome edits for improved mevalonate flux

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The strains produced up to 12 mg/L of GA₃ and up to 17 mg/L GA₄ in small-scale cultivations

How mechanisms explain interfield cooperation: biological-chemical study of plant growth hormones in Utrecht and Pasadena, 1930-1938

This article examines to what extent a particular case of cross-disciplinary research in the 1930s was structured by mechanistic reasoning. For this purpose, it identifies the interfield theories that allowed biologists and chemists to use each other's techniques and findings, and that provided the basis for the experiments performed to identify plant growth hormones and to learn more about their role in the mechanism of plant growth. In 1930, chemists and biologists in Utrecht and Pasadena began to cooperatively study plant growth. I will argue that these researchers decided to join forces because they believed to rely on each other's findings and methods to solve their research problems adequately. In the course of the cooperation, organic chemists arrived at isolating plant growth hormones by using a test method developed in plant physiology. This achievement, in turn, facilitated biologists' investigation of the mechanism of plant growth. Researchers eventually believed to have the means to study the relation between a substance's molecular structure and its physiological activity. The way they conceptualized the problem of identifying hormones and unraveling the mechanism of plant growth, as well as their actual research actions are compatible with the new mechanists' account of mechanism research. The study illustrates that focusing on researchers' mechanistic reasoning can contribute considerably to explaining the structure of cross-disciplinary research projects.

Pre-drought priming sustains grain development under post-anthesis drought stress by regulating the growth hormones in winter wheat (Triticum aestivum L.)

Drought stress during grain filling is the most yield-damaging to wheat. Pre-drought priming facilitated the wheat plants to sustain grain development against the post-anthesis drought stress by modulating the levels of growth hormones. Post-anthesis drought stress substantially reduces grain yield in wheat (Triticum aestivum L.) due to impaired grain development associated with imbalanced levels of growth hormones. To investigate whether pre-drought priming could sustain grain development in wheat by regulating favorable levels of growth hormones under post-anthesis drought conditions, the plants of a drought-sensitive (Yangmai-16) and drought-tolerant (Luhan-7) wheat cultivar were exposed to a moderate drought stress during tillering (Feekes 2 stage) for priming, and then, a subsequent severe drought stress was applied from 7 to 14 days after anthesis. The results showed that drought-stressed plants of both cultivars showed a decline in flag leaf water potential, chlorophyll contents, photosynthetic rate, grain size initiation, and grain filling as compared to well-watered plants; however, decline in these traits was less in pre-drought primed (PD) plants than in nonprimed (ND) plants. Under drought stress, the PD plants regulated higher concentrations of zeatin and zeatin riboside, indole-3-acetic acid, gibberellins, and lower abscisic acid content in grains, resulting in higher endosperm cell division and expansion, grain size initiation, grain-filling rate and duration, and finally higher grain dry weights as compared to ND plants. The PD plants of both cultivars showed higher potential to tolerate the post-anthesis drought stress, but more effect was displayed by drought-tolerant cultivar. From the achieved results, it was concluded that pre-drought priming facilitated the wheat plants to sustain higher grain development and yield against the most yield-damaging post-anthesis drought stress by modulating the levels of growth hormones.

Influence of microbial diversity and plant growth hormones in compost and vermicompost from fermented tannery waste

This study focuses on the effect of the epigeic earthworm Eudrilus eugeniae (with and without addition) to transform solid state fermented (SSF) and submerged (SmF) state fermented TFL mixed with cow dung and leaf litter into value added products in compost and vermicompost bioreactors respectively. The significant role of microbes was identified during compost and vermicompost process. In addition, three important phytohormones (Indole 3-acetic acid, Gibberellic acid, Kinetin) were also detected in the compost and vermicompost products. The results revealed that the maximum amount of plant hormones were available in the vermicompost products which may be due to the joint action of earthworm and microorganisms. The overall results confirmed that the vermicomposting process produced a greater value added product.