Differences in Virulence among PVY Isolates of Different Geographical Origins When Infecting an Experimental Host under Two Growing Environments Are Not Determined by HCPro

• Main Authors: Mongia Makki, Francisco Javier del Toro, Khouloud Necira, Francisco Tenllado, Fattouma Djilani-Khouadja, Tomás Canto
• Format: Article
• Language: English
• Published: MDPI AG 2021-05-01
• Series: Plants
• Subjects: HCPro and virus adaptation; <i>Potyvirus</i> virulence and HCPro; HCPro suppression of silencing; <i>Potyvirus</i> evolution
• Online Access: https://www.mdpi.com/2223-7747/10/6/1086

The contribution of the HCPro factors expressed by several PVY isolates of different geographical origins (one from Scotland, one from Spain, and several from Tunisia) to differences in their virulence in <i>Nicotiana benthamiana</i> plants was investigated under two growing conditions: standard (st; 26 °C and current ambient levels of CO₂), and climate change-associated (cc; 31 °C and elevated levels of CO₂). In all cases, relative infection symptoms and viral titers were determined. The viral <i>HCPro</i> cistrons were also sequenced and amino-acid features of the encoded proteins were established, as well as phylogenetic distances. Additionally, the abilities of the HCPros of several isolates to suppress silencing were assessed under either growing condition. Overall, viral titers and infection symptoms decreased under cc vs. st conditions. However, within each growing condition, relative titers and symptoms were found to be isolate-specific, with titers and symptom severities not always correlating. Crucially, isolates expressing identical HCPros displayed different symptoms. In addition, all HCPro variants tested displayed comparable silencing suppression strengths. Therefore, HCPro alone could not be the main determinant of the relative differences in pathogenicity observed among the PVY isolates tested in this host, under the environments considered.