The Role Of Plant Protein NTH202 In The Regulation Of Salicylic Acid Pathways By Whitefly Salivary Protein Bt56

The whitefly Bemisia tabaci(Hemiptera:Aleyrodidae)is an important agricultural pest.In recent years,the invasion and wide distribution of Mediterranean(MED)and Middle East Asia Minor(MEAM1)whitefly,has caused serious losses to the production of many crops in China.While ingesting phloem sap,phloem-feeding insects such as whitefly secrete saliva into plant to regulate plant defenses.So far,only a few salivary proteins have been identified in phloem-feeding insects,the mechanism underlying the regulation of plant defenses by salivary effectors remains largely unknown.In this study,we investigated the role of Bt56,a saliva effector of whitefly,in plant-whitefly interaction and the molecular mechanisms underlying the regulation of plant defense responses.Previous studies have shown that the salivary effector Bt56 is a low molecular weight protein,which is specifically expressed in the whitefly primary salivary gland.Overexpression of Bt56 gene in planta increases the susceptibility of tobacco to whitefly and elicit plant SA signaling pathway.Protein-protein interaction assays show that Bt56 protein directly interacts with a tobacco transcription factor NTH202 and further study showed that NTH202 was able to interact with Bt56 from different species of the whitefly complex.The expression levels of NTH202 gene in Bt56-overexpressed and whitefly-infested tobacco were significantly lower than that in control plants.The transcript knockdown of NTH202 did not change plant phenotype,but significantly increased the survival and fecundity of whiteflies on tobacco.The levels of SA did not change significantly in NTH202-silenced tobacco plants.However,when tobacco plants were infested by whiteflies,the levels of SA in both NTH202-silenced and control tobacco increased significantly and the level of SA in NTH202-silenced tobacco was significantly higher than that in control tobacco.These data indicate that host plant protein NTH202 does not directly affect SA in non-infested plant but it represses whitefly-induced SA accumulation.Therefore,we infer that besides acting as a transcription factor in nucleus,NTH202 may have other functions in cytosol that are conservatively influenced by whitefly Bt56.In conclusion,we identified a host target protein NTH202 in tobacco that is involved in the regulation of plant defenses by a whitefly saliva effector.These findings reveal an important molecular mechanism of how phloem feeders regulate plant defenses for their own benefit,which provide important clues to understand the invasion mechanism of whitefly,selection of insect-resistant crop varieties and development of novel control strategies.