Chloroplast Engineering for Herbicide Resistance via Photosynthesis Proteins

Introduction

Photosynthesis is an important site for plant metabolism. All light reactions in this process take place in the chloroplast, and the two main players are photosystem Ⅱ (PS Ⅱ) and photosystem I (PS I). Herbicides that can affect plant photosynthesis were discovered in the 1950s, some of which act on the electron flow of PS Ⅱ, and others by inducing the electron flow of PS I. Binding of PS Ⅱ-inhibiting herbicides to the D1 protein in the PS Ⅱ reaction center blocks the electron transport of PS II, thereby producing triplet chlorophyll and singlet oxygen, and inducing membrane lipid peroxidation. The PS I electron acceptor may accept electrons from the iron-sulfur protein F_a/F_b. Herbicides that inhibit PS I lead to the production of hydroxyl radicals in the form of free radicals, leading to lipid peroxidation. Photosynthesis-inhibiting herbicide-induced lipid peroxidation disrupts membrane integrity, leading to cellular disturbance and phytotoxicity.

Fig. 1. Stages I, II and III of plant metabolism degrade active ingredients to develop resistance to herbicides. (Gaines T A, et al., 2020)

Solutions

The two main sites of herbicide action in photosynthetic electron transport are inhibition of electron transport from PS Ⅱ and transfer of electron flow through PS I. Our engineers have been working to confer herbicide resistance in crops by encoding PS Ⅱ encoded by the psbA gene in the chloroplast genome. In addition, we constructed resistance to PS I-specific herbicides in a model tobacco system by expressing glutathione reductase from E. coli and copper/zinc chloroplast superoxide dismutase from pea.

The D1 protein has long been considered to be a herbicide demucinization protein. Based on the research on the functional and molecular docking of the binding of photosynthetic herbicides to the Q_B site of D1 protein in plant PS Ⅱ, Lifeasible introduced the insensitive psbA gene into the chloroplast genome to develope a highly tolerant photosynthetic herbicide resistance traits. We have successfully developed transgenic crops for a variety of herbicides that inhibit PS Ⅱ and PS I, including phenyl carbamates, pyrazines, triazines, triazolines, uracils, amides, ureas, benzene thiadiazines, nitriles, phenylpyrazines and bipyridines. Our available solutions for herbicide resistant via photosynthesis proteins include:

• Identification of structural conservation of the D1 protein and Q_B binding site in oxyphotosynthetic organisms.
• Estimation of the binding affinity of herbicides to the Q_B binding site of D1 protein by photochemical and photosystem II inhibition fluorescence methods.
• Molecular docking study of the interaction between the Q_B-binding site of herbicide D1 protein.

Features of Our Strategy

• By inhibiting the electron transport of PS Ⅱ and the transfer of electron transport of PS I.
• Mutations have differences in binding affinity for different classes of herbicides.
• The reaction center of a purple photosynthetic bacteria homologous to PS Ⅱ was used as a model.
• Amino acid residues associated with sensitivity and specificity to PS Ⅱ inhibitors were determined by random induction and site-directed mutagenesis.
• Modification of the Q_B-binding site of the D1 protein by site-directed mutagenesis to improve herbicide susceptibility.

Photosynthesis-inhibiting herbicides act as photosynthetic electron transport inhibitors and decouplers. Making crops tolerant to them by encoding photosynthetic proteins is an ideal strategy. Lifeasible has extensive knowledge and experience in the engineering of herbicide resistance via herbicide-insensitive enzymes. Our mission is to provide customers with comprehensive, reliable, professional solutions to accelerate your research. If you are interested in our solutions, please contact us at any time.

References

1. Gaines T A, Duke S O, Morran S, et al. (2020) Mechanisms of evolved herbicide resistance[J]. Journal of Biological Chemistry. 295(30): 10307-10330.
2. Fuerst E P, Norman M A. (1991) Interactions of herbicides with photosynthetic electron transport[J]. Weed Science. 39(3): 458-464.