Abstract
The newly-identified SWEETs are high-capacity, low-affinity sugar transporters with important roles in numerous physiological mechanisms where sugar efflux is critical. SWEETs are desirable targets for manipulation by pathogens and their expression may be transcriptionally reprogrammed during infection. So far, few plant SWEET transporters have been functionally characterized, especially in grapevine. In this study, in the Botrytis-susceptible variety “Trincadeira,” we thoroughly analyzed modifications in the gene expression profile of key SWEET genes in Botrytis cinerea-infected grape berries. VvSWEET7 and VvSWEET15 are likely to play an important role during fruit development and Botrytis infection as they are strongly expressed at the green and mature stage, respectively, and were clearly up-regulated in response to infection. Also, B. cinerea infection down-regulated VvSWEET17a expression at the green stage, VvSWEET10 and VvSWEET17d expression at the veraison stage, and VvSWEET11 expression at the mature stage. VvSWEET7 was functionally characterized by heterologous expression in Saccharomyces cerevisiae as a low-affinity, high-capacity glucose and sucrose transporter with a K m of 15.42 mM for glucose and a K m of 40.08 mM for sucrose. VvSWEET7-GFP and VvSWEET15-GFP fusion proteins were transiently expressed in Nicotiana benthamiana epidermal cells and confocal microscopy allowed to observe that both proteins clearly localize to the plasma membrane. In sum, VvSWEETs transporters are important players in sugar mobilization during grape berry development and their expression is transcriptionally reprogrammed in response to Botrytis infection.
Highlights
Grapevine (Vitis vinifera L.) is prone to a wide range of pathogens that cause production and quality losses
The transcript levels of VvSWEET10 peaked at veraison, and VvSWEET2a gene expression was similar during grape berry development
The expression of most VvSWEET genes, including VvSWEET7, in Botrytis-elicited grape berry cell suspensions originating from the pulp of berries from Cabernet Sauvignon berries, was modified in a similar way to the changes observed in infected grape berries from the field experiment when they occurred, with the exception of only VvSWEET1 and VvSWEET17a, whose expression was repressed or unaltered, respectively (Supplementary Figure 2)
Summary
Grapevine (Vitis vinifera L.) is prone to a wide range of pathogens that cause production and quality losses. Necrotrophs obtain nutrients from dead cells, which are killed during the infection process They cause necrosis secreting hydrolytic enzymes that degrade the cell wall (van Kan, 2006), secrete toxins (Govrin et al, 2006; Dalmais et al, 2011), and hijack the plant enzymatic machinery, promoting programmed cell death (Cantu et al, 2009). The causal agent of the grey mold disease in more than 200 plants (Elad et al, 2004), is one of the most important grapevine pathogens (Haile et al, 2017) It is a necrotrophic fungus with a short biotrophic phase (Veloso and van Kan, 2018). Up-regulation of sugar transporters was observed during pathogen infection in Arabidopsis thaliana and Pinus pinaster cultured cells (Truernit et al, 1996; Azevedo et al, 2006)
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