Plants and insects have both benefited and harmed one another through the ages. Plants provide sweet nectar as food to insects, in exchange for, insects carry pollen caught on their bodies to other plants. This aids their benefactor plants in the reproduction process. Contrastingly, harm may come to the plant as insects prey on the plant for food and plants can be defoliated in short order by these feeding insects. In order to protect themselves from harmful insects plants produce a variety of noxious phytochemicals. Phenolic glucosides are one of the defensive secondary metabolites produced by plants for this purpose. The whitefly named Bemisia tabaci, one of the most devastating crop pests is a cosmopolitan, highly polyphagous and can seriously reduce crop yields by feeding on phloem, transmitting plant viruses, and excreting honeydew.
Phenolic glucosides are toxic phytochemicals strongly affect growth, development, and behavior of whitefly (Bemisia tabaci). Recent research studies have found that, whitefly has acquired the plant-derived phenolic glucoside malonyltransferase gene BtPMaT1 to neutralize phenolic glucosides. In plants, an important modification of phenolic glycosides involves their malonylation, which is regulated by an enzyme known as phenolic glycosides malonyltransferases. These enzymes can catalyze the transfer of a malonyl group from malonyl coenzymes A (CoA) to the phenolic glycosides and play an important role in various processes, including xenobiotic detoxification. Bemisia tabaci feeds on plants of the Salicaceae, can also readily cope with phenolic glycosides and may even use them as feeding and oviposition stimulants.
Whitefly neutralizes the defensive phenolic glycosides either by using specific detoxifying enzymes, decreasing the enzyme activity of β-glucosidases, directly sequestering phenolic glycosides, or converting them to salicylaldehyde. Results of a study showed that genome of whitefly harbors a plant-specific and horizontally transferred gene, BtPMaT1, encoding a phenolic glucoside malonyltransferase. This is an unexpected route by which Bemisia tabaci has evolved its extraordinary ability to overcome the defenses of its host plants. This ability of whiteflies to detoxify plant defense compounds is pivotal for their adaptive evolution. It is shown that, the horizontal transfer of BtPMaT1 gene empower whiteflies with the ability to attach a malonyl group to phenolic glucosides, rendering these common plant-produced secondary metabolites almost completely innocuous. The metabolic detoxification process in B. tabaci most likely relies on a conjugation reaction similar to herbicide metabolism in certain plants, whereby malonyltransferase can catalyze detoxification by conjugating the herbicide or an intermediate metabolite with malonyl-CoA. Moreover, BtPMaT1 malonylation might promote the solubility and export of the ingested phenolic glycosides.
According to scientists, understanding of the molecular basis of B. tabaci’s polyvalent ability to overcome plant defenses is recognized as a key for the development of durable pest control strategies. For instance, whiteflies were found to suppress plant defenses by leveraging the crosstalk between plant defense hormones, and they may even do so in neighboring plants through the induction of specific volatile signals. Several whitefly salivary proteins have been identified as effectors that are involved in this apparent manipulation of plant defenses by eliciting the salicylic acid-signaling pathway. Whiteflies also have attained the ability to detoxify defense compounds by acquiring a gene from plants. It showed that B. tabaci is prone to accept horizontal transfer genes and this may help to circumvent resistance traits of host plants. This insight into a co-evolutionary process that facilitates host plant adaptation in insects also reveals that interfering with laterally transferred genes can be a highly effective way to combat pests.
Source
Jixing Xia, Zhaojiang Guo, Zezhong Yang, Haolin Han, Shaoli Wang, Haifeng Xu, Xin Yang, Fengshan Yang, Qingjun Wu, Wen Xie, Xuguo Zhou, Wannes Dermauw, Ted C.J. Turlings, Youjun Zhang, Whitefly hijacks a plant detoxification gene that neutralizes plant toxins, Cell, Volume 184, Issue 7, 2021, Pages 1693-1705.e17,ISSN 0092-8674, https://doi.org/10.1016/j.cell.2021.02.014.