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

Abstract

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.

microRNAs: Key Regulators in Plant Responses to Abiotic and Biotic Stresses via Endogenous and Cross-Kingdom Mechanisms

“…Practical validation is required for amiRNA applications. Indeed, the transfer of amiRNA targeting potato spindle tuber viroids (PSTVd) into tomato plants causes developmental retardation and reproductive defects in the plants [147]. Furthermore, amiRNAs inadvertently silenced sterol glycosyltransferase 1 (SISGT1) in tomatoes, leading to impairment of the growth hormone signaling pathway and impeding the growth of amiR-PSTVd plants [148].…”