The Involvement of HSP70 and HSP90 inTomato Yellow Leaf Curl Virus Infection in Tomato Plants and Insect Vectors

Cellular chaperones HSP70 and HSP90 are involved in Tomato yellow leaf curl virus (TYLCV) infection. TYLCV is a begomovirus transmitted by the whitefly Bemisia tabaci to tomato and other crops. In infected tomato and B. tabaci vector, chaperones are redistributed, from soluble to aggregated state. Together with chaperones and viral proteins, ubiquitin, 26S proteasome subunits and autophagy protein ATG8, all were found in large protein aggregates. The appearance of these aggregates containing protein quality control elements and infectious virions can be considered as markers of a successful virus invasion. Capturing of HSP70/HSP90 in aggregates results in a decrease of the free chaperones pool, which triggers the transcription of HSP encoding genes under the control of heat stress transcription factors. Indeed, TYLCV infection downregulates the heat stress response of plants grown at high temperatures, and alleviates cell death caused by the other stresses. Stress response mitigation is used by TYLCV for successful multiplication. Even though HSP70 and HSP90 are similarly recruited in TYLCV aggregates, their roles in viral multiplication are different. HSP70, but not HSP90, is important for the viral coat protein shuttling from cytoplasm into nuclei. HSP70 impairment leads to decreased viral amounts, while HSP90 inhibition causes an inactivation of cellular protein degradation and consequently promotes the accumulation of viral proteins.