Plasmodesmata targeting and intercellular trafficking of Tomato spotted wilt tospovirus movement protein NSm is independent of its function in HR induction

A Plant Immune Receptor Adopts a Two-Step Recognition Mechanism to Enhance Viral Effector Perception

“…Based on the results obtained in this study and our earlier findings (Zhao et al, 2016;Zhu et al, 2017), we propose a two-step recognition model explaining how the Sw-5b NLR is activated upon perception of the viral effector NSm ( Figure 6D). In this model, when the NSm protein level is high, both the Sw-5b SD and NB-ARC-LRR perceive NSm and Sw-5b is rapidly activated to initiate a defense response (Figure 6Di).…”

“…The tomato Sw-5b NLR (Brommonschenkel et al, 2000;Spassova et al, 2001) recognizes the viral movement protein NSm from tospoviruses to activate immune responses (Hallwass et al, 2014;Peiro et al, 2014;Zhao et al, 2016). Our recent study demonstrated that Sw-5b recognizes a conserved 21amino-acid region in NSm (NSm 21 ) to provide a broad-spectrum resistance to the American type of tospoviruses (Zhu et al, 2017).…”

Non-Structural Protein NSm of Tomato Spotted Wilt Virus Is an Avirulence Factor Recognized by Resistance Genes of Tobacco and Tomato via Different Elicitor Active Sites

“…Our previously constructed five mutant forms of TSWV NSm carrying alanine substitutions at aa residues 54–56 (A54–56), 93 and 94 (A93–94), 122–125 (A122–125), 154 (A154), and 269–274 (A269–274), which were defective in both plasmodesmata (PD) targeting and tubule formation [ 25 , 35 ], fused with YFP (NSmA54–56-YFP, NSmA93–94-YFP, NSmA122–125-YFP, NSmA154-YFP, and NSmA269–274-YFP, respectively) were mobilized into A. tumefaciens and agroinfiltrated into N. benthamiana leaves ( Figure 4 A). Results of confocal laser scanning microscopy showed that none of these alanine substitution mutants localized at the PD, consistent with prior studies of these mutants [ 25 , 35 ]. Next, the ability of these NSm mutants defective in tubule formation to trigger HR was evaluated.…”

“…However, the activity of NSs as an RNA silencing suppressor is distinct from its activity as an Avr factor [ 42 ]. Recently, it has been suggested that the intercellular trafficking of NSm is uncoupled from its function in HR induction; this has become evident from the analysis of NSm mutants defective in targeting PD and cell-to-cell movement but capable of inducing Sw-5b-mediated HR [ 25 , 43 ]. Our results obtained in this study and previous studies support the hypothesis that rather than recognizing the domains involved in virus replication, movement, or gene-silencing suppression, R protein may have first evolved to recognize the most conserved domains of viral effector proteins [ 25 ].…”

“…Wild type and mutant versions of the NSm gene were fused with the yellow fluorescent protein (YFP) gene to generate C-terminal fusions of YFP (NSm-YFP, NSmC118Y-YFP, NSmT120N-YFP, NSm115-135aa-YFP, NSmA54–56-YFP, NSmA93–94-YFP, NSmA122–125-YFP, NSmA154-YFP, and NSmA269–274-YFP) as described previously [ 16 , 25 ].…”