Environmental stresses affect agricultural production worldwide, leading to yield reductions of many crops. Drought and heat are the most serious abiotic stresses, especially in countries with hot climates. Drought, together with heat, usually stimulates plant pathogens such as viruses, bacteria, fungi, and insects. Interactions between the plant environment and pathogens modulate the plant defence responses (Prasch & Sonnewald, 2013), either weakening or enhancing them (Atkinson & Urwin, 2012).An increasing research body indicates that plant viruses modulate host responses to changes in their environment such as wounding, elevated salinity, high temperature, and atmospheric CO 2 . These changes are accompanied by alterations in the virus biology such as titre, virulence, and transmission efficiency (Bergès et al., 2020;van Munster et al., 2017).Abiotic stresses may affect the life cycle of viruses as well as the interactions between host susceptibility factors and viruses.Conversely, viruses can influence the plant response to abiotic stresses. For example, turnip mosaic virus (TuMV)-infected plants display an enhanced expression of defence genes, which is abolished in those plants exposed to abiotic stresses. Deactivation of defence responses leads to a higher susceptibility of plants to virus (Prasch & Sonnewald, 2013). Abiotic stress sensing through the Ca 2+

A growing body of research points to a positive interplay between viruses and plants. Tomato yellow curl virus (TYLCV) is able to protect tomato host plants against extreme drought. To envisage the use of virus protective capacity in agriculture, TYLCV-resistant tomato lines have to be infected first with the virus before planting. Such virus-resistant tomato plants contain virus amounts that do not cause disease symptoms, growth inhibition, or yield loss, but are sufficient to modify the metabolism of the plant, resulting in improved tolerance to drought. This phenomenon is based on the TYLCV-dependent stabilization of amounts of key osmoprotectants induced by drought (soluble sugars, amino acids, and proteins). Although in infected TYLCV-susceptible tomatoes, stress markers also show an enhanced stability, in infected TYLCV-resistant plants, water balance and osmolyte homeostasis reach particularly high levels. These tomato plants survive long periods of time during water withholding. However, after recovery to normal irrigation, they produce fruits which are not exposed to drought, similarly to the control plants. Using these features, it might be possible to cultivate TYLCV-resistant plants during seasons characterized by water scarcity.

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