Comparative metabolomics of temperature sensitive resistance to wheat streak mosaic virus (WSMV) in resistant and susceptible wheat cultivars.

In order to evaluate wheat resistance to wheat streak mosaic virus (WSMV) at low temperature and resistance breakdown at high temperature, metabolic profile of WSMV-resistant (R) and susceptible (S) wheat cultivars were analyzed. Metabolites were detected by UPLC-QTOF/MS in leaves of R and S plants challenged with WSMV at 20 °C and 32 °C, 24, 48 and 72 h post inoculation (hpi). WSMV and mock inoculated plants were used for discriminating the most significant metabolites and metabolic pathways affected at those temperatures. At 24 hpi/20 °C and 48 hpi/20 °C, the most important metabolites in R plants were coumarins, a limited number of lipids, and unknown compounds, while at 72 hpi/20 °C, in addition to coumarins, alkaloids and several amino acids were increased. Compared to 24 and 48 hpi, at 72hpi, in R plants most metabolic pathways were up-regulated at 20 °C. These resistance-related specific pathways included amino acid metabolism, lipid metabolism and alkaloids pathways. Also, several pathways were up-regulated at 32 °C.These combined heat stress and pathogen related pathways, included lipid metabolism and amino acid metabolism. Some carbohydrate metabolism pathways were considered as heat stress related pathways and could be associated with resistance breakdown. On the other hand, the increased expression of lipid compounds, especially 24 hpi at 32 °C in R plant, can be attributed to plant adaptation to combined stressors such as pathogen and high temperature. Increased susceptibility of R plants at 32 °C coincided with a down-regulated expression of components of signal transduction pathways or in a decreased level of metabolites related to this pathway, especially at a later time after infection, leading to decreased metabolite signaling. Decrease of signaling compounds under combined stress is a possible outcome of deactivating WSMV specific signaling networks leading to compatible response in R plants. The significance of these findings considering the recent increase of global temperature and the challenge of breakdown of temperature sensitive resistance to some plant viruses is discussed.