Ministry of Agriculture Key Lab of Molecular Biology of Crop Pathogens and Insects, Institute of Insect Sciences, Zhejiang University, 310058 Hangzhou, China.
Ministry of Agriculture Key Lab of Molecular Biology of Crop Pathogens and Insects, Institute of Insect Sciences, Zhejiang University, 310058 Hangzhou, China
Proc Natl Acad Sci U S A. 2019 Jan 8;116(2):490-495. doi: 10.1073/pnas.1714990116. Epub 2018 Dec 24.
Phloem-feeding insects feed on plant phloem using their stylets. While ingesting phloem sap, these insects secrete saliva to circumvent plant defenses. Previous studies have shown that, to facilitate their feeding, many phloem-feeding insects can elicit the salicylic acid- (SA-) signaling pathway and thus suppress effective jasmonic acid defenses. However, the molecular basis for the regulation of the plant's defense by phloem-feeding insects remains largely unknown. Here, we show that Bt56, a whitefly-secreted low molecular weight salivary protein, is highly expressed in the whitefly primary salivary gland and is delivered into host plants during feeding. Overexpression of the gene promotes susceptibility of tobacco to the whitefly and elicits the SA-signaling pathway. In contrast, silencing the whitefly gene significantly decreases whitefly performance on host plants and interrupts whitefly phloem feeding with whiteflies losing the ability to activate the SA pathway. Protein-protein interaction assays show that the Bt56 protein directly interacts with a tobacco KNOTTED 1-like homeobox transcription factor that decreases whitefly performance and suppresses whitefly-induced SA accumulation. The orthologous genes are highly conserved but differentially expressed in different species of whiteflies. In conclusion, Bt56 is a key salivary effector that promotes whitefly performance by eliciting salicylic acid-signaling pathway.
取食韧皮部的昆虫使用口针取食植物韧皮部。在摄取韧皮部汁液的同时，这些昆虫会分泌唾液来规避植物防御。先前的研究表明，为了促进取食，许多取食韧皮部的昆虫可以引发水杨酸（SA）信号通路，从而抑制有效的茉莉酸防御。然而，取食韧皮部的昆虫对植物防御的调控分子基础在很大程度上仍然未知。在这里，我们表明，烟粉虱分泌的一种低分子量唾液蛋白 Bt56 在烟粉虱的初级唾液腺中高度表达，并在取食过程中被输送到宿主植物中。基因的过表达促进了烟草对白粉虱的易感性，并引发了 SA 信号通路。相比之下，沉默烟粉虱基因显著降低了烟粉虱在宿主植物上的性能，并中断了烟粉虱的韧皮部取食，使它们失去了激活 SA 途径的能力。蛋白-蛋白相互作用分析表明，Bt56 蛋白直接与烟草 KNOTTED 1 类同源盒转录因子相互作用，降低了烟粉虱的性能，并抑制了烟粉虱诱导的 SA 积累。该基因的同源基因在不同的粉虱物种中高度保守，但表达水平不同。总之，Bt56 是一种关键的唾液效应因子，通过引发水杨酸信号通路来促进粉虱的性能。
