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.

Background We have previously demonstrated that an aldo‐keto reductase (AKR) from Echinochloa colona (EcAKR4‐1) can metabolize glyphosate and confers glyphosate resistance. This study aims to investigate if the EcAKR4‐1 orthologs from Lolium rigidum also play a role in glyphosate resistance in non‐target‐site based, glyphosate‐resistant (R) L. rigidum populations from Western Australia. Results The full‐length L. rigidum AKR gene (LrAKR4C10) orthologous to EcAKR4‐1, together with a distinct LrAKR1, were cloned from plants of a glyphosate‐susceptible (S) (VLR1) and three glyphosate R L. rigidum populations (WALR50, WALR60 and WALR70). Reverse transcription quantitative polymerase chain reaction (RT‐qPCR) results showed that basal expression levels of the two LrAKR genes did not differ between the R and S populations, but their expression was significantly induced by glyphosate (up to 4.3‐fold) or 2,4‐D treatment (up to 3.4‐fold) in R populations. Escherichia coli cells transformed respectively with LrAKR4C10 and LrAKR1 were more tolerant to glyphosate. Rice (Oryza sativa) seedlings overexpressing each of the two LrAKR gene survived glyphosate rates that were lethal to the green fluorescence protein (GFP) control plants. Structural modeling predicts a similar way of glyphosate binding and detoxification by LrAKR4C10 and EcAKR4‐1, but an alternative way of glyphosate binding by LrAKR1. Relatively lower capacity of the two LrAKRs in conferring glyphosate resistance than the known EcAKR4‐1 was discussed in relation to structural interaction. Conclusion Glyphosate‐induced higher expression of the two LrAKR genes in L. rigidum populations contributes to a moderate level of glyphosate resistance likely through enhanced glyphosate metabolism. The herbicide 2,4‐D can also induce the LrAKR expression, indicating the potential antagonistic effect of 2,4‐D to glyphosate. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Background: Herbicides are the major tool for controlling large populations of yield depleting weeds. However, overreliance on herbicides has resulted in weed adaptation and herbicide resistance. In recent years, early flowering weed species related to herbicide resistance is emerging, which may cause seed loss before crop harvest, creating a new problem for non-chemical weed management. However, mechanisms regulating early flowering in weedy species is rarely investigated. Results: The MADS-box gene family plays an important role in flowering time regulation and floral organogenesis. In this study, a homolog gene of AGAMOUS sub-family (referred to as PfAG5) of the MADS-box family was cloned from plants of an early flowering Polypogon fugax population resistant to the ACCase inhibitor herbicide (clodinafop-propargyl). The PfAG5 gene was functionally characterized in Arabidopsis thaliana. Over-expression of the PfAG5 gene in Arabidopsis resulted in early flowering with abnormal flowers (e.g. small petals, short plants and reduced seed set) compared to the wild type. The expression of the PfAG5 gene was high in leaves and flowers, but low in pods in transgenic Arabidopsis. The PfAG5 gene was earlier and higher expressed in the resistant (R) than the susceptible (S) P. fugax plants. Furthermore, one protein (FRIGIDA-like protein) interacting with PfAG5 in R P. fugax was identified by the yeast two-hybrid system with relevance to flowering time regulation. Conclusions: These results suggest that the PfAG5 gene is prominently involved in modulating early flowering in P. fugax. This study provides the first evidence for the regulation mechanism of early flowering in an herbicide resistant weed species.