Safener activity and metabolic resistance to herbicides in dicots

In agriculture, safeners are synthetic compounds used to protect cereals from herbicide injury during herbicide application to targeted weed species. Safeners protect crops by increasing the detoxification rate of the herbicide. They enhance the expression of proteins that are part of the xenome, such as gluthatione S-transferase (GST) or cytochrome P450 monooxygenases (P450s) (Skipsey et al., 2011).

It has been demonstrated that safeners do not protect dicot plants against herbicide injury. Nevertheless, it has been shown that these compounds produce transcriptional changes in some dicot species. For example, in the model plant Arabidopsis thaliana there is an increase in the expression of genes involved in three phases of the detoxification pathway, such as GTSs and glucosyltransferases (UGTs) (Behringer et al., 2011). Thus, A.thaliana is an ideal species to study the genetic components that regulate the expression of the detoxifying enzymes and observe the effect on dicot plants (Brazier-Hicks et al., 2008).

The regular application of herbicides has led to the evolution of organisms resistant to herbicides. These organisms have characteristic genes and mechanisms that allow the survival and reproduction in the presence of the herbicide (Powles and Yu, 2010). Interestingly, numerous populations of the dicot weed Amaranthus are resistant to multiple families of herbicides. For example, the population of A.tuberculatus MCR (designated for McLean County mesotrine- and atrazine-resistant) is resistant to 4-hydroxyphenylpyruvate dioxygenase (HPPD) herbicides such as mesotrione, as well as to atrazine. (Ma et al., 2013; Ma et al., 2015). A.palmeri has evolved resistance to multiple herbicides with a variety of modes of action such as microtubule-, photosystem II (PS II)-, acetolactate synthase (ALS)-, 5-enol-pyruvylshikimate-3-phosphate synthase (EPSPS)-,protoporphyrinogen oxidase (PPO) and 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibitors (Kupper et al., 2017). There is increasing evidence that Amaranthus species have developed herbicide resistance through enhanced herbicide metabolism. From this, it is clear that while safeners cannot invoke metabolism based herbicide resistance in dicots, such endogenous signalling systems are present in these plants.

In this project, the study of safener and resistance mechanisms in dicot plants will identify genes/proteins involved in herbicide detoxification in the model dicot plant A.thaliana and in agronomically important dicot weeds. Furthermore, the metabolic pathway for the detoxification of herbicides will be determined in dicot plants. This will lead to a more detailed understanding of the molecular and metabolic effect of resitance/safeners in dicot plants.
Behringer, C., Bartsch, K. and Schaller, A. (2011) 'Safeners recruit multiple signalling pathways for the orchestrated induction of the cellular xenobiotic detoxification machinery in Arabidopsis', Plant Cell Environ, 34(11), 1970-85.