Project description:Polypogon fugax is a common winter weed in China and other Asia countries. We have previously found a P. fugax biotype (R) resistant to acetyl co-enzyme A carboxylase (ACCase) herbicides also cannot be effectively controlled by some acetolactate synthase (ALS) herbicides. This study evaluated the level of resistance to four ALS herbicides (metsulfuron-methyl, chlorsulfuron, monosulfuron, pyribambenz isopropyl) in the R biotype and the associated resistance mechanism. The R biotype exhibited moderate level of resistance to metsulfuron-methyl (6.0-fold) compared with the sensitive biotype (S). Sequence analysis of ALS gene revealed that two ALS genes existed in P. fugax. However, no substitution associated with ALS resistance mechanism were found in ALS genes between the S and R biotypes. The activity of ALS enzyme isolated from the R biotype was inherently higher and less sensitive to metsulfuron-methyl than the S biotype. Glutathione S-transferases (GST) activity was also less sensitive to metsulfuron-methyl in the R than as the S biotypes. Malathion, a cytochrome P450 (CYP) monooxygenase inhibitor, had much greater synergistic effect with metsulfuron-methyl on the R than as the S plants, reducing the ED50 value (herbicide dose to inhibit growth by 50%) of metsulfuron-methyl by 23- and 6-fold, respectively, suggesting that CYP mediated enhanced metabolism might contribute to the resistance to ALS herbicides. These results suggest that metsulfuron-methyl resistance in the R biotype was associated with the up-regulated ALS enzymatic activity and the GST and CYP-mediated enhanced herbicide metabolism.
Project description:The evolution of herbicide resistance in weedy plants leads to various adaptation traits including flowering time and seed germination. In our previous studies, we found an association of the early flowering phenotype with the ACCase inhibitor herbicide resistance genotype in a population of Polypogon fugax. MADS-box transcription factors are known to play pivotal roles in regulating plant flowering time. In this study, a SHORT VEGETATIVE PHASE (SVP)-like gene, belonging to the StMADS11 subfamily in the MADS-box family, was cloned from the early flowering P. fugax population (referred to as PfMADS16) and resistant to the herbicide clodinafop- propargyl. Overexpression of the SVP-like gene PfMADS16 in Arabidopsis thaliana resulted in early flowering and seed abortion. This is consistent with the phenotypic characters of resistant P. fugax plants, but contrary to the conventional role of SVP-like genes that usually suppress flowering. In addition, down regulation of the seed formation gene AtKTN1 in flowers of PfMADS16 transgenic Arabidopsis plants indicates that PfMADS16 may be indirectly associated with seed viability. Furthermore, one protein (PfMADS2) from the APETALA1 (AP1) subfamily interacting with PfMADS16 in P. fugax was identified with relevance to flowering time regulation. These results suggest that the PfMADS16 gene is an early flowering regulation gene associated with seed formation and viability in resistant P. fugax population. Our study provides potential application of PfMADS16 for integrated weed management (such as genetic-based weed control strategies) aiming to reduce the soil weed seedbank.
Project description:Quantification of germination characteristics between herbicide-resistant and -susceptible weeds might provide methods to control resistant weeds and permit better prediction of evolution and persistence of herbicide resistance. This study aimed to compare the germination characteristics of Asian minor bluegrass (Polypogon fugax) populations that are resistant or susceptible to quizalofop-p-ethyl under controlled conditions, which the resistance mechanism is involved in glutathione S-transferases (GSTs) metabolism-based resistance. No major differences in seed germination were found at diverse temperatures, pH ranges, and light conditions. However, a significant difference that seed response to a gradient of osmotic and salt stress between the resistant and susceptible P. fugax populations were found. Two stress response genes (P5CS-1 and CDPK-2) in P. fugax were likely involved in germination rate as well as germination speed in response to these stresses. Subsequently, population verification demonstrated that P5CS-1 and CDPK-2 genes may be linked to the resistance mechanism. Additionally, the two genes play an important role in response to salt stress and osmotic stress as shown by transcript abundance after stress treatments. Our findings suggest that the variation of the germination characteristics in P. fugax associates with the presence of GST-endowed resistance mechanism.