The unfolded protein response in grapevine: abiotic and biotic stresses induce the expression of VvbZIP60, VvbZIP17, VvBIP3, and VvIRE1

A wide range of stresses can lead to the accumulation of unfolded or misfolded proteins in the lumen of the endoplasmic reticulum (ER), a condition known as ER stress. To restore proteostasis, eukaryotic cells activate a signaling network called the unfolded protein response (UPR). In Vitis vinifera, two arms of the UPR have been identified: the IRE1/bZIP60 arm and the bZIP17 arm. Notably, no putative ortholog of bZIP28 has been found in V. vinifera, whereas this is the case for Brassicaceae species. We demonstrated that VvbZIP60 undergoes unconventional splicing upon treatment with dithiothreitol (DTT) and tunicamycin (TM), both classical ER stress inducers. Moreover, after testing several abiotic factors, we observed a strong transcriptional activation of UPR-related genes in response to heat and osmotic stresses, as well as copper exposure. Grapevine is also subject to a broad range of microbial challenges, including pathogens such as Plasmopara viticola and Botrytis cinerea. Both pathogens triggered UPR genes activation in grapevine leaves and berries. Interestingly, VvbZIP17 was also upregulated in green berries, a developmental stage associated with strong basal resistance to B. cinerea. Collectively, these findings suggest that the IRE1/bZIP60 and bZIP17 arms of the UPR are not only structurally conserved in grapevine but are also transcriptionally responsive to a variety of abiotic and biotic stresses.