Differential expression of genes associated with non-target site resistance in Poa annua with target site resistance to acetolactate synthase inhibitors

Abstract

Background: Poa annua is a pervasive grassy, self-pollinating, weed that has evolved resistance to 10 different herbicide modes-of-action, third most of all weed species. We investigated constitutive overexpression of genes associated with non-target site resistance (NTSR) in POAAN-R3 and the response of those genes when treated with trifloxysulfuron despite the biotype having a known target site mutation in acetolactate synthase (ALS).

Results: Despite having an ALS target site mutation, POAAN-R3 still had a transcriptomic response to herbicide application that differed from a susceptible biotype. We observed differential expression of genes associated with transmembrane transport and oxidation-reduction activities, with differences being most pronounced prior to herbicide treatment.

Conclusions: In the P. annua biotype we studied with confirmed target site resistance to ALS inhibitors, we also observed constitutive expression of genes regulating transmembrane transport, as well as differential expression of genes associated with oxidative stress after treatment with trifloxysulfuron. This accumulation of mechanisms, in addition to the manifestation of target site resistance, could potentially increase the chance of survival when plants are challenged by different modes of action.

Keywords: RNA-Seq; non-target site resistance; transcriptomics; turfgrass.

Figure 1

The number of differentially expressed genes in herbicide‐resistant (POAAN‐R3) and susceptible biotypes of Poa annua. Expression analysis was performed on a total of 28 006 genes.

Figure 2

Biological processes, cellular component and molecular function gene ontology enrichment of genes differentially expressed between herbicide‐resistant and ‐susceptible Poa annua biotypes before treatment calculated with topGO sorted by the number of significant terms for each category. Positive and values indicate values indicate GO categories overexpressed and suppressed in the resistant (POAAN‐R3) biotype, respectively, compared to the susceptible biotype.

Figure 3

Number of significant GO terms enriched in genes overexpressed in the resistant biotype POAAN‐R3 compared to the susceptible biotype at 2, 6, 12, 24 and 48 h after treatment, as calculated with topGO.

Figure 4

Relative expression between herbicide‐resistant (POAAN‐R3) and ‐susceptible Poa annua biotypes for three selected genes. Gene expression level was measured by qRT‐PCR (closed dots, solid line), normalized against elongation factor 1α and ratios calculated using the ΔΔCt method; relative expression changes was also calculated from RNASeq data (open dots, dash line). Panel A: ABC‐2 type transporter (Genbank accession GCZY01000308), Panel B: catalase isozyme 2 (Genbank accession GCZY01006429) and Panel C: Cytochrome P450 (Genbank accession GCZY01008731).