Expression Profiles of <i>psbA, ALS, EPSPS</i>, and Other Chloroplastic Genes in Response to PSII-, ALS-, and EPSPS-Inhibitor Treatments in <i>Kochia scoparia</i>

Abstract

Kochia (Kochia scoparia L. Schrad.), also known as tumbleweed, is an economically important annual C4 broadleaf weed found throughout the US Great Plains. Several herbicides with different modes of action are used in the management of kochia. The effect of commonly used herbicides on the expression of their target site(s) and photosynthetic/chloroplastic genes is poorly understood in weed species, including kochia. The objective of this research was to characterize the expression profiles of herbicide target-site genes, KspsbA, KsALS, and KsEPSPS upon treatment with PSII- (e.g. atrazine), ALS- (e.g. chlorsulfuron), and EPSPS- (e.g. glyphosate)-inhibitors, respectively, in kochia. Furthermore, the expression of genes involved in photosynthesis (e.g. KsRubisco, KsCAB, and KsPPDK) was also determined in response to these herbicide treatments. KspsbA was strongly upregulated (>200-fold) 24 h after atrazine treatment. Transcript levels of the KsALS or KsEPSPS genes were 7 and 3-fold higher 24 h after chlorsulfuron or glyphosate treatment, respectively. KsRubisco, a Calvin cycle gene important for CO2 fixation, was upregulated 7 and 2.6-fold 8 and 24 h after glyphosate and chlorsulfuron treatments, whereas it downregulated 8 and 24 h after atrazine treatment. The transcript levels of KsPPDK remained unchanged after glyphosate treatment but increased 1.8-fold and decreased 2-fold at 24 h after chlorsulfuron and atrazine treatments, respectively. KsCAB remained unchanged after chlorsulfuron treatment, but was downregulated after glyphosate and atrazine treatments. The results show that herbicide treatments not only affect the respective target-site gene expression, but also influence the genes involved in the critical photosynthetic pathway.