Abstract
Conyza bonariensis (hairy fleabane) is one of the most problematic and widespread glyphosate-resistant weeds in the world. This highly competitive weed species significantly interferes with crop growth and substantially decreases crop yield. Despite its agricultural importance, the molecular mechanisms of glyphosate resistance are still unknown. The present RNA-Seq study was performed with the goal of identifying differentially expressed candidate transcripts (genes) related to metabolism-based non-target site glyphosate resistance in C. bonariensis. The whole-transcriptome was de novo assembled from glyphosate-resistant and -sensitive biotypes of C. bonariensis from Southern Brazil. The RNA was extracted from untreated and glyphosate-treated plants at several timepoints up to 288 h after treatment in both biotypes. The transcriptome assembly produced 90,124 contigs with an average length of 777 bp and N50 of 1118 bp. In response to glyphosate treatment, differential gene expression analysis was performed on glyphosate-resistant and -sensitive biotypes. A total of 9622 genes were differentially expressed as a response to glyphosate treatment in both biotypes, 4297 (44.6%) being up- and 5325 (55.4%) down-regulated. The resistant biotype presented 1770 up- and 2333 down-regulated genes while the sensitive biotype had 2335 and 2800 up- and down-regulated genes, respectively. Among them, 974 up- and 1290 down-regulated genes were co-expressed in both biotypes. In the present work, we identified 41 new candidate target genes from five families related to herbicide transport and metabolism: 19 ABC transporters, 10 CYP450s, one glutathione S-transferase (GST), five glycosyltransferases (GT), and six genes related to antioxidant enzyme catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD). The candidate genes may participate in metabolic-based glyphosate resistance via oxidation, conjugation, transport, and degradation, plus antioxidation. One or more of these genes might ‘rescue’ resistant plants from irreversible damage after glyphosate treatment. The 41 target genes we report in the present study may inform further functional genomics studies, including gene editing approaches to elucidate glyphosate-resistance mechanisms in C. bonariensis.
Highlights
Weed interference is among the most significant biotic constraints to crop yield and global food security, causing up to $100 billion in damage annually [1,2,3]
The present study aimed to study the molecular changes of C. bonariensis in response to glyphosate treatment in the long term after herbicide treatment
We identified a total of 41 candidates differentially expressed genes associated to the herbicide metabolism phases of oxidation (CYP450), conjugation (GST and GT), transport (ABC transporters), and protection/compensation [20,30]
Summary
Weed interference is among the most significant biotic constraints to crop yield and global food security, causing up to $100 billion in damage annually [1,2,3]. Weed species with widespread occurrence and highly competitive capacity with crops that are difficult to manage are damaging to agricultural security. Conyza bonariensis (L.) Cronq., commonly called hairy fleabane, is one of the most threatening and difficult weed species to manage around the world [4,5]. This Asteraceae species is native to the Americas and has a cosmopolitan distribution [4]. The evolved glyphosate resistance (GR) is a critical factor that complicates controlling weeds in the field [7]
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