CRISPR'd Rapeseed gets Herbicide Resistance

Updated: Apr 2, 2020

Rapeseed, which is also known as Brassica napus, is a yellow flower that is mainly grown due to having seeds that are abundant in oil. Rapeseed is normally grown in winter or spring every year.

The main uses of rapeseed are:

  • It is a very common vegetable oil used around the world

  • Rapeseed is also used to make biodiesel

  • It can be used as a lubricant for artificial joints too

Industrial rapeseed contains very high levels of erucic acid which is toxic for the body and can cause damage to the heart, thus it is not for human consumption! Instead, canola oil was specifically bred from the original rapeseed to have less than 2% erucic acid which is known to be a safe level for human consumption.

The Food and Agriculture Organization reported that 39.5 million tons of rapeseed had been produced globally in 2000. The global production of rapeseed steadily increased over the years and the latest dataset is from 2018, whereby it was reported that 75 million tons of rapeseed had been produced worldwide. The data can be observed in the graph below.

It is clear that rapeseed is in high demand, but farmers face issues whilst trying to grow rapeseed cultivars due to the presence of weeds such as monocots and dicots that greatly affect the quality of the rapeseed crop. There are various methods farmers can use to remove the weeds, one of these methods is using herbicides. Herbicides are chemicals that are used to kill unwanted plants. There are herbicides called ALS inhibitors, these work by inhibiting acetolactate synthase (ALS), an enzyme found in plants which is required for the synthesis of branched amino acids. Therefore, the weed becomes deprived of amino acids and withers.

How do Herbicides Work?

Conservation of plant biodiversity is essential for the ecosystem, it is suggested that herbicides should only be used at a concentration that allows crop quality and growth, and in order to promote biodiversity, the herbicide should not remove all the weeds, this balance can be achieved by using the lowest possible concentration of the herbicide. However, using a low dose of herbicides has implications too, it can result in herbicide resistance in the weed itself which would cause a lot of problems for the farmers.

Herbicides are very efficient at removing weeds but can affect the rapeseed crop too, studies have shown that herbicides affect the rapeseed cultivar resulting in low crop quality. A study was conducted in China, whereby researchers used CRISPR-Cas9 base editing to introduce a single base mutation in the bnALS1 and bnALS3 genes which code for ALS in rapeseed cultivar. The unedited and CRISPR-edited rapeseed cultivars were then sprayed with the herbicide tribenuron-methyl (an ALS inhibitor). It was found that the unedited rapeseed was damaged by small concentrations of the herbicide, and the CRISPR-edited rapeseed was unaffected by the herbicide even at high concentrations. Thereby, showing that even a point mutation can provide herbicide resistance in rapeseed cultivars, and this has potential applications for rapeseed cultivars in the future.

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