Down-regulation of tomato STEROL GLYCOSYLTRANSFERASE 1 perturbs plant development and facilitates viroid infection

Potato spindle tuber viroid (PSTVd) is a plant pathogen naturally infecting economically important crops such as tomato (Solanum lycopersicum). Here, we aimed to engineer tomato plants highly resistant to PSTVd and developed several S. lycopersicum lines expressing an artificial microRNA (amiRNA) against PSTVd (amiR-PSTVd). Infectivity assays revealed that amiR-PSTVd-expressing lines were not resistant but instead hypersusceptible to the viroid. A combination of phenotypic, molecular, and metabolic analyses of amiRNA-expressing lines non-inoculated with the viroid revealed that amiR-PSTVd was accidentally silencing the tomato STEROL GLYCOSYLTRANSFERASE 1 (SlSGT1) gene, which caused late developmental and reproductive defects such as leaf epinasty, dwarfism, or reduced fruit size. Importantly, two independent transgenic tomato lines each expressing a different amiRNA specifically designed to target SlSGT1 were also hypersusceptible to PSTVd, thus demonstrating that down-regulation of SlSGT1 was responsible for the viroid-hypersusceptibility phenotype. Our results highlight the role of sterol glycosyltransferases in proper plant development and indicate that the imbalance of sterol glycosylation levels favors viroid infection, most likely by facilitating viroid movement.

This work was supported by grants from Ministerio de Ciencia e Innovación (MCIN, Spain), Agencia Estatal de Investigación (AEI, Spain), and Fondo Europeo de Desarrollo Regional (FEDER, European Union) (RTI2018-095118-A-100 and RYC-2017-21648 to A.C, PRE2019-088439 to AEC, PIE2020-116765RB-I00 to P.L. and PID2020-114691RB-I00 to J.-A.D, AGL2017-88842-R to AF and TA, and Severo Ochoa Programme for Centres of Excellence in R&D CEX2019-000902-S), Generalitat Valenciana (PROMETEU/2021/056 to P.L.), Generalitat de Catalunya (2017SGR710 and CERCA Programme).

With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation CEX2019-000902-S.

Peer reviewed