Abstract
Herbicide resistance can be either target-site or non-target-site based. The molecular mechanisms underlying non-target-site resistance (NTSR) are poorly understood, especially at the level of gene expression regulation. MicroRNAs (miRNAs) represent key post-transcriptional regulators of eukaryotic gene expression and play important roles in stress responses. In this study, the miR397 gene from Beckmannia syzigachne (referred to as bsy-miR397) was functionally characterized to determine its role in regulating fenoxaprop-P-ethyl resistance. We showed that (1) bsy-miR397 transcript level is constitutively higher in resistant than in sensitive B. syzigachne plants, whereas bsy-Laccase expression and activity show the opposite trend, and (2) bsy-miR397 suppresses the expression of bsy-Laccase in tobacco, indicating that it negatively regulates bsy-Laccase at the transcriptional level. We found evidences that miR397/laccase regulation might be involved in fenoxaprop-P-ethyl NTSR. First, the rice transgenic line overexpressing OXmiR397 showed improved fenoxaprop-P-ethyl tolerance. Second, following activation of bsy-Laccase gene expression by CuSO4 treatment, fenoxaprop resistance in B. syzigachne tended to decrease. Therefore, we suggest that bsy-miR397 might play a role in fenoxaprop-P-ethyl NTSR in B. syzigachne by down-regulating laccase expression, potentially leading to the enhanced expression of three oxidases/peroxidases genes to introduce an active moiety into herbicide molecules in Phase-2 metabolism. Bsy-miR397, bsy-Laccase, and other regulatory components might form a regulatory network to detoxify fenoxaprop-P-ethyl in B. syzigachne, supported by the differential expression of transcription factors and oxidases/peroxidases in the rice transgenic line overexpressing OXmiR397. This implies how down-regulation of a gene (laccase) can enhance NTSR. Our findings shed light on the daunting task of understanding and managing complex NTSR in weedy plant species.
Highlights
Herbicide resistance can be achieved by target-site and nontarget-site based mechanisms (Powles and Yu, 2010)
Expression of bsymiR397 was significantly higher in the 30 plants each of the R1, R2, and R3 populations than in the S population, whereas the expression of bsy-Laccase was significantly higher in the S plants than in the R1, R2, and R3 plants (Figure 1)
As expected, OXmiR397overexpressing plants had lower levels of OsLAC expression and laccase activity than the wild type (WT) plants (Figure 5). These results indicated that miR397/laccase regulation can provide protection from fenoxaprop-P-ethyl damage in OXmiR397overexpressing transgenic rice, suggesting that miR397/laccase might be involved in fenoxaprop-P-ethyl non-target-site resistance (NTSR)
Summary
Herbicide resistance can be achieved by target-site and nontarget-site based mechanisms (Powles and Yu, 2010). Non-target-site resistance (NTSR) refers to any mechanisms not belonging to TSR (Délye, 2013). NTSR can be mediated via several mechanisms (Délye, 2013; Yu and Powles, 2014), and often under polygenic control (Busi et al, 2013; Gaines et al, 2014; Duhoux et al, 2015; Gardin et al, 2015). Most recent studies have focused on metabolic resistance (Gaines et al, 2014; Duhoux et al, 2015; Gardin et al, 2015; Pan et al, 2016), and very few of them have investigated the molecular mechanisms underlying NTSR
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