HSP70 plays an ambiguous role during viral infections in plants

Abstract

Heat shock proteins (HSPs) are a family of mainly stressinduced proteins whose primary function is to refold denatured proteins. HSPs are divided into six groups according to their relative molecular mass and primary structure homology (Wang et al. 2004, Park and Seo 2015). The genes that encode HSPs are found in different cell compartments, and HSP expression is controlled by transcriptional factors known as heat shock factors (HSFs) (Haq et al. 2019). In particular, HSP70 is arguably the most conserved protein family among all the organisms, from bacteria to plants and animals. The number of members in different HSP70 families ranges from 18 in Arabidopsis thaliana and 20 in Solanum tuberosum, through 30 in Oryza sativa to 61 in Nicotiana tabacum (Liu et al. 2018, Song et al. 2019). HSP70 are crucial for cells as constitutive and ubiquitously expressed proteins, but HSP70 expression is also induced, not only by heat shock (HS), but by almost all types of plant stresses as well (Park and Seo 2015, Usman et al. 2017). In the classical model for stress activation of HSPs, the presence of stress-induced unfolded proteins in the cell causes the release of HSPs from their constitutive inhibitory association with HSF monomers, although this model could involve more pathways, especially at temperatures that do not unfold proteins. The unfolded