23 material. Importantly, the xylem sap-specific exoproteome pinpointed Nlp2 and Nlp3 49 as single effectors required for successful V. dahliae colonization. 50 51 Author Summary 52 Verticillium spp. infect hundreds of different plants world-wide leading to enormous 53 economic losses. Verticillium wilt is a disease of the vasculature. The fungus colonizes 54 the xylem of its host plant where it exploits the vascular system to colonize the whole 55 plant. Therefore, the fungus spends part of its lifetime in this nutrient-low and 56 imbalanced environment where it is inaccessible for disease control treatments. This 57 lifestyle as well requires the fungus to react to plant defense responses by secreting 58 specific effector molecules to establish a successful infection. We addressed the 59 differences in media-dependent secretion responses of Verticillium longisporum. We 60 identified a broad response pattern induced by several media, and a similar response 61 (but with some distinct differences) for the plant-related environments: the pectin-rich 62 medium SXM and xylem sap from the host rapeseed. Importantly, we show that the 63 necrosis and ethylene inducing-like proteins Nlp2 and Nlp3 are xylem sap-specific 64 proteins that are required for full V. dahliae pathogenicity on tomato. These factors 65 play a role during the colonization phase and represent potential targets for new control 66 strategies for Verticillium wilt. 67 68 associated molecular patterns (PAMPs); examples include the fungal cell-wall polymer 95 chitin [16]. PAMP perception elicits a basal defense response which halts colonization 96 by non-adapted pathogens and results in PAMP-triggered immunity (PTI). Host-97 adapted pathogens circumvent PTI by secretion of specific effector proteins as 98 virulence factors for different phases of the infection cycle [17]. These secreted 99 effectors may act passively or actively to combat plant defense responses [18]. 100 Well known examples of fungal effectors include the Avr4 and Ecp6 effectors from the 101 leaf mold fungus Cladosporum fulvum that bind to chitin oligosaccharides via a 102 carbohydrate-binding module (CBM) or LysM domain, respectively [18-21]. Similarly, 103 a chitin scavenging function has also been assigned to Cp1 in V. dahliae strain XH-8. 104 CP1 knockout mutants were affected in cotton virulence [22]. This chitin protection 105 leads to the suppression of the PTI of the plant and shields the fungal cell wall from 106 plant chitinases that hydrolyze chitin [18-21]. Other fungal effectors such as 107 metalloproteases possess enzymatic activity and are able to truncate plant chitinases 108 that attack the fungal cell wall [23, 24]. Toxins provide another means for pathogens 109 to attack plant hosts. For example, necrosis and ethylene inducing-like proteins (NLP) 110 induce immune responses and cell death in host tissues and are conserved among 111 fungi including Verticillium spp. [25, 26]. V. dahliae isolates encode up to eight NLP 112 homologs [26, 27] whereas most other fungi gene...