Enrico Gozio

Herbicide resistance is an emerging phytosanitary threat, causing serious yield and economic losses. Although this phenomenon has been widely studied, only recently has the role of epigenetic factors in its occurrence been considered. In the present study, we analyzed the microRNA-mediated regulation in Echinochloa oryzicola (Vasinger) Vasinger (late-watergrass) of the expression of cytochromes P450, glutathione S-transferase (GST), and eIF4B, all of which are enzymes involved in profoxydim (AURA^®) detoxification. Before and after profoxydim application, the expression profiles of microRNAs (miRNAs) were selected for their ability to target the genes considered, and their targets were assessed by means of RT-qPCR. Susceptible and resistant biotypes showed different responses to this herbicide. After profoxydim application, in resistant biotypes, osa-miR2099-5p, ath-miR396b, osa-miR395f, osa-miR396a-5p, osa-miR166a-5p, osa-miR166d-5p, gra-miR8759, and gma-miR396f were not triggered, allowing the expression of CYP81A, GSTF1, and eIF4B genes and the herbicide’s detoxification. Meanwhile, the transcription of ata-miR166c-5p, ath-miR847, osa-miR5538, and gra-miR7487c was triggered, down-regulating CYP71AK2, CYP72A254, CYP72A122, and EcGST expression. In susceptible biotypes, the herbicide stimulated ata-miR166c-5p, ath-miR847, osa-miR5538, gra-miR7487c, osa-miR166a-5p, and gra-miR8759, down-regulating their respective target genes (CYP72A122, CYP71AK2, EcGST, CYP72A254, CYP81A12, and eIF4B). A better understanding of the role of miRNA-mediated epigenetic regulation in herbicide resistance will be useful in planning more targeted and sustainable methods for controlling this phytosanitary threat.

Several mechanisms involved in weed herbicide resistance are unknown, particularly those acting at the epigenetic level, such as the capacity of small-non-coding RNAs (sncRNAs) to target messenger RNAs of genes involved in herbicide detoxification. The transcription of these sncRNAs is stimulated by epigenetic factors, thereby affecting gene expression. This study was carried out in order to evaluate, for the first time in Echinochloa crus-galli (L.) P. Beauv. (barnyardgrass), the capacity of miRNAs to regulate the expression of genes associated with bispyribac-sodium detoxification. The expression profiles of eight miRNAs with a high degree of complementarity (≥80%) with mRNAs of genes involved in herbicide detoxification (CYP450, GST and eIF4B) were determined by qRT-PCR before and after herbicide spraying. Five of the miRNAs studied (gra-miR7487c, gma-miR396f, gra-miR8759, osa-miR395f, ath-miR847) showed an increased expression after herbicide application in both susceptible and resistant biotypes. All the miRNAs, except gra-miR8759, were more highly expressed in the herbicide-resistant biotypes. In specimens with increased expression of miRNAs, we observed reduced expression of the target genes. The remaining three miRNAs (ata-miR166c-5p, ath-miR396b-5p and osa-miR5538) showed no over-expression after herbicide treatment, and no difference in expression was recorded between susceptible and resistant biotypes. Our results represent a first overview of the capacity of miRNAs to regulate the expression of genes involved in bispyribac-sodium detoxification in the genus Echinochloa. Further research is required to identify novel miRNAs and target genes to develop more focused and sustainable strategies of weed control.