Chloroplast Engineering for Herbicide Resistance via Acetolactate Synthase

Introduction

Acetolactate synthase (ALS), also known as acetohydroxy acid synthase (AHAS), plays an important role in the biosynthesis of branched-chain amino acids in plants and many microorganisms. ALS is the first enzyme to catalyze the synthesis of the branched-chain amino acids valine, leucine and isoleucine in the chloroplast. In addition, ALS has been the target of several herbicides such as sulfonylureas, imidazolinones, triazolopyrimidines, and pyrimidinyloxybenzoates. Inhibiting ALS depletes branched-chain amino acids, leading to the death of susceptible species. These herbicides all inhibit ALS through their unique modes. They are generally considered to be faster-acting growth inhibitors than glyphosate. ALS-resistant herbicides are widely used in agriculture because of their high herbicidal efficacy, high crop selectivity, low application rates, and low levels of mammalian toxicity.

Fig. 1. Chloroplast transformation with aadA and mutated ALS (mALS). (Shimizu M, et al., 2008)

Solutions

ALS confers herbicide tolerance by mutating several amino acid residues and has been reported in herbicide-resistant plants such as rice, tobacco, and Arabidopsis. Since ALS is a major target of at least five structurally distinct herbicides, our engineers have been working to engineer herbicide resistance through plant ALS genes encoding catalytic subunits, including imidazolinones (IMIs), sulfonylureas (SU), triazolopyrimidines (TP), pyrimidinyl carboxylates (PC) and sulfonamido-carbonyl-triazolinones (SCT). We have successfully developed transplanted plants that are tolerant to PC, IMIs and SU/PC.

Here, Lifeasible used the male ALS gene as a sustainable marker to introduce the mALS gene into the chloroplast genome and examine the susceptibility of transformants to ALS-inhibiting herbicides. In addition, we mutated multiple amino acids in ALS to alter the structural or spatial conformation of the enzyme, thereby reducing the protein's affinity for herbicides and resulting in herbicide resistance. Our available solutions for herbicide resistant via ALS include:

• Effects of mALSs overexpression on plant growth.
• Feedback regulation of regulatory subunits in vivo.
• Dependence of herbicide resistance on each mutation.
• Availability of various combinations of different mutations and herbicides.

Features of Our Strategy

• The mALS gene can be used as a sustainable marker, as well as a selectable marker for nuclear transformation.
• The mALS gene showed selective tolerance to various herbicides.
• Multiple herbicides can interfere with different domains of the ALS molecule, reducing the occurrence of herbicide-resistant weeds in programs that rotate different herbicides.
• A single mALS locus exists in Arabidopsis and rice that can directly implement gene targeting strategies.
• Contributing to the implementation of a new strategy based on a combination of multiple herbicides and mALSs in crop rotation.
• Allowing the production of transgenic plants with only the ALS gene mutation without integrating any other external DNA sequences.

The mALS gene is a potent sustainable marker with selective tolerance to different types of herbicides. Rotation of different herbicides on transgenic plants carrying the ALS gene is very effective. 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. Shimizu M, Goto M, Hanai M, et al. (2008) Selectable tolerance to herbicides by mutated acetolactate synthase genes integrated into the chloroplast genome of tobacco[J]. Plant physiology. 147(4): 1976-1983.
2. Shimizu M, Kawai K, Kaku K, et al. (2011) Application of mutated acetolactate synthase genes to herbicide resistance and plant improvement[J]. Herbicides, Theory and Applications. 10: 193-212.