VvSWEET7 Is a Mono- and Disaccharide Transporter Up-Regulated in Response to Botrytis cinerea Infection in Grape Berries

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 Botrytissusceptible 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.

Modelling the physiological relevance of sucrose export repression by an Flowering Time homolog in the long‐distance phloem of potato

“…Experimental characterizations of SWEET transport are performed in heterologous expression systems, with expression levels and presence of co‐factors likely different from the in planta conditions, suggesting that particularly measured v max values should be treated with caution when extrapolating them to in planta transport. Indeed, reported values ranged from 0.0012 (Chen et al, 2012) to 0.148 mol m −3 s −1 (Breia et al, 2020). Therefore, we first explored a broad range of v max values (such that over the entire stem length it equals 0 to 100% of the total loading rate with a K m of 10 mM) and quantified the effect and physiological significance on sucrose delivery.…”

“…(c) Delivery yield along a range of efflux rates (v max ). The orange dots represent experimentally measured v max values (Breia et al, 2020; Chen et al, 2012). (d) Effect of the affinity constant (K m ) on efflux.…”

“…Importantly, Abelenda and co‐workers reported significant effects of StSWEET11 RNAi knockdown and overexpression on stem apoplast sucrose levels, supporting the physiological relevance of unblocked StSWEET11‐mediated sucrose export in the stem (Abelenda et al, 2019). Importantly, SWEET transport rates were characterized in heterologous expression systems, resulting in highly variable reported maximum transport rates (Breia et al, 2020; Chen et al, 2012), with no data available for in planta transport rates. Using our model, we find that for SWEET mediated export to significantly affect sucrose transport characteristics, transport rates should lie in the upper range of the experimentally reported values.…”

The Molecular Regulation of Carbon Sink Strength in Grapevine (Vitis vinifera L.)

“…Overexpression of the VvSWEET4 in grapevine hairy roots increases sugar transportation and content and enhances resistance to soilborne pathogens ( Meteier et al, 2019 ). Similarly, VvSWEET7 is a mono- and disaccharide transporter and its expression is up-regulated in response to Botrytis cinerea infection in grapes ( Breia et al, 2019 ). VvSWEET10 has a broad spectrum of sugar transport functions.…”

Data_Sheet_1.doc

“…Broad spectrum of sugar transport; Enhance biotic stress Chong et al, 2014;Breia et al, 2019;Meteier et al, 2019;Zhang et al, 2019 of VvTMT1 have been detected by heterologous expression in the hxt-null mutant yeast (Zeng et al, 2011). Recent function analysis indicated PbTMT4 regulates the accumulation of sugars in the vacuole and it is a strong contributor to fructose, glucose, and sucrose accumulation in frutescence of pears (Pyrus bretschneideri) (Cheng et al, 2018).…”