BackgroundParaquat is one of the most effective herbicides used to control weeds in agricultural management, while the pernicious weed goosegrass (Eleusine indica) has evolved resistance to herbicides, including paraquat. Polyamines provide high-level paraquat resistance in many plants. In the present study, we selected three polyamines, namely, putrescine, spermidine, and spermine, as putative genes to investigate their correlation with paraquat resistance by using paraquat-resistant (R) and paraquat-susceptible (S) goosegrass populations.ResultsThere was no significant difference in the putrescine nor spermine content between the R and S biotypes. However, 30 and 90 min after paraquat treatment, the spermidine concentration was 346.14-fold and 421.04-fold (P < 0.001) higher in the R biotype than in the S biotype, but the spermidine concentration was drastically reduced to a marginal level after 90 min. Since the transcript level of PqE was low while the spermidine concentration showed a transient increase, the PqE gene was likely involved in the synthesis of the paraquat resistance mechanism, regulation of polyamine content, and synthesis of spermidine and spermine. PqTS1, PqTS2, and PqTS3 encode transporter proteins involved in the regulation of paraquat concentration but showed different transcription patterns with synchronous changes in polyamine content.ConclusionEndogenous polyamines (especially spermidine) play a vital role in paraquat resistance in goosegrass. PqE, PqTS1, PqTS2, and PqTS3 were speculated on the relationship between polyamine metabolism and paraquat resistance. To validate the roles of PqE, PqTS1, PqTS2, and PqTS3 in polyamine transport systems, further research is needed.

20Background : Paraquat is one of the most effective herbicides used to control weeds 21 in agricultural management, while the pernicious weed goosegrass (Eleusine indica) 22 has evolved resistance to herbicides, including paraquat. Polyamines provide high-23 level paraquat resistance in many plants. In the present study, we selected three 24 polyamines, namely, putrescine, spermidine, and spermine, as putative genes to 25 investigate their correlation with paraquat resistance by using paraquat-resistant (R) 26 and paraquat-susceptible (S) goosegrass populations. 27Results: There was no significant difference in the putrescine nor spermine content 28 between the R and S biotypes. However, 30 and 90 min after paraquat treatment, the 29 spermidine concentration was 346.14-fold and 421.04-fold (P < 0.001) higher in the R 30 biotype than in the S biotype, but the spermidine concentration was drastically reduced 31 to a marginal level after 90 min. Since the transcript level of PqE was low while the 32 spermidine concentration showed a transient increase, the PqE gene was likely 33 involved in the synthesis of the paraquat resistance mechanism, regulation of 34 polyamine content, and synthesis of spermidine and spermine. PqTS1, PqTS2, and 35 PqTS3 encode transporter proteins involved in the regulation of paraquat concentration 36 but showed different transcription patterns with synchronous changes in polyamine 37 content. 38 Conclusion: Endogenous polyamines (especially spermidine) play a vital role in 39 paraquat resistance in goosegrass. PqE, PqTS1, PqTS2, and PqTS3 were speculated on 40 the relationship between polyamine metabolism and paraquat resistance. To validate 41 the roles of PqE, PqTS1, PqTS2, and PqTS3 in polyamine transport systems, further 42 research is needed. 43 3 44 45

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Eleusine indica (goosegrass) is a problematic weed worldwide known for its multi-herbicide tolerance/resistance biotype. However, a genetic transformation method in goosegrass has not been successfully established, making a bottleneck for functional genomics studies in this species. Here, we report a successful Agrobacterium-mediated transformation method for goosegrass. Firstly, we optimized conditions for breaking seed dormancy and increasing seed germination rate. A higher callus induction rate from germinated seeds was obtained in N6 than in MS or B5 medium. Then the optimal transformation efficiency of the gus reporter gene was obtained by infection with Agrobacterium tumefaciens culture of OD600 = 0.5 for 30 min, followed by 3 days of co-cultivation with 300 μmol/L acetosyringone. Concentrations of 20 mg L−1 kanamycin and 100 mg L−1 timentin were used to select the transformed calli. The optimal rate of regeneration of the calli was generated by using 0.50 mg L−1 6-BA and 0.50 mg L−1 KT in the culture medium. Then, using this transformation method, we overexpressed the paraquat-resistant EiKCS gene into a paraquat-susceptible goosegrass biotype MZ04 and confirmed the stable inheritance of paraquat-resistance in the transgenic goosegrass lines. This approach may provide a potential mechanism for the evolution of paraquat-resistant goosegrass and a promising gene for the manipulation of paraquat-resistance plants. This study is novel and valuable in future research using similar methods for herbicide resistance.