Abstract
The Sw-5 gene cluster encodes protein receptors that are potentially able to recognize microbial products and activate signaling pathways that lead to plant cell immunity. Although there are several Sw-5 homologs in the tomato genome, only one of them, named Sw-5b, has been extensively studied due to its functionality against a wide range of (thrips-transmitted) orthotospoviruses. The Sw-5b gene is a dominant resistance gene originally from a wild Peruvian tomato that has been used in tomato breeding programs aiming to develop cultivars with resistance to these viruses. Here, we provide an overview starting from the first reports of Sw-5 resistance, positional cloning and the sequencing of the Sw-5 gene cluster from resistant tomatoes and the validation of Sw-5b as the functional protein that triggers resistance against orthotospoviruses. Moreover, molecular details of this plant–virus interaction are also described, especially concerning the roles of Sw-5b domains in the sensing of orthotospoviruses and in the signaling cascade leading to resistance and hypersensitive response.
Highlights
Orthotospoviruses cause substantial losses in crop production worldwide (Pappu et al, 2009)
The absence of Solanaceae domain (SD)-CC does not interfere with NSm recognition and hypersensitive response (HR) triggering, but transgenic plants transformed with a truncated Sw-5b gene lacking these domains are not resistant to orthotospoviruses (Chen et al, 2016)
In contrast to the findings with Sw-5b, co-expression of Sw-5a and tomato spotted wilt virus (TSWV) NSm does not result in HR triggering (De Oliveira et al, 2016), which could explain why Sw-5a-transformed tobacco plants are susceptible to TSWV (Spassova et al, 2001)
Summary
Orthotospoviruses (family Tospoviridae) cause substantial losses in crop production worldwide (Pappu et al, 2009). Frontiers in Plant Science | www.frontiersin.org de Oliveira et al The Sw-5 Gene Cluster is solely responsible for a broad-spectrum resistance to orthotospoviruses (Spassova et al, 2001; Hallwass et al, 2014; Leastro et al, 2017).
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