Insect pests are one of the major causes of crop loss worldwide. Currently, synthetic pesticides are widely used to control pests in agricultural fields, but their overuse often causes serious environmental problems and threatens human health. Different from pesticides, some environmental-friendly chemical elicitors (also known as plant strengtheners), such as benzothiadiazole and jasmonates, although unable to directly kill insects, can induce or enhance plant resistance to pests, emerging as promising substitutes for pesticides. However, most of the reported chemical elicitors can reduce plant growth through hormonal crosstalk, which is undesirable for achieving high yield in crops, thereby limiting their use in agricultural practices. In a recent study, Yonggen Lou's group at Zhejiang University in China reported the identification of a new plant strengthener, 4-fluorophenoxyacetic acid (4-FPA), which can not only enhance plant resistance to piercing-sucking insects but also increase crop yields in the field (Wang et al., 2020).
4-FPA, a synthesized phenoxyalkanoic acid derivative, was first identified as a candidate chemical elicitor that induces resistance in rice to the white-backed planthopper (WBPH; He et al., 2015). 4-FPA is absorbed by roots and leaves and then transported to leaf sheaths, where it is immediately converted into 4-fluorophenol (4-FP). Either alone or in combination, 4-FPA and 4-FP increase amino acid and peroxidase levels but decrease H2O2 and flavonoid levels in rice plants, with no observed effects on the transcript levels of genes involved in the hormonal pathways. Using H2O2 as an electron acceptor, flavonoids and 4-FP are subsequently catalyzed by peroxidases to form phenolic polymers in plant parenchyma cells. As many phenolic polymer particles (diameter, 1–5 μm) are larger than those of WBPH stylets (diameter, ∼2 μm), it was proposed that they may prevent WBPH stylets from reaching the phloem through physical blocking, thereby decreasing food intake (Figure 1 ). Interestingly, the spraying of 4-FPA not only decreased WBPH populations but also increased rice grain yield in the field. Furthermore, 4-FPA was found to confer broad-spectrum resistance to other piercing-sucking insects tested, with no harmful effects on spiders, which are the main predatory natural enemies of insect pests on rice plants.
Figure 1.
Schematic Diagram Illustrating how 4-FPA Protects Cereal Crops from Piercing-Sucking Insects.
4-FPA, 4-fluorophenoxyacetic acid; 4-FP, 4-fluorophenol; WBPH, white-backed planthoppers.
In conclusion, 4-FPA is a promising plant strengthener that can control devastating cereal insect pests and boost crop yield, without negative effects on plant growth due to hormonal reprogramming. This study on 4-FPA provides a potential strategy for agricultural pest control and introduces new ideas for designing and exploiting additional plant strengtheners in the near future.
References
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