Fig. 1

Summary of the key processes of stress response regulation by HSP90 in tomato plants, and down-regulation by TYLCV infection. Functional loss of the cellular chaperone HSP90 causes the dissociation of the 26S proteasome and a significant decrease of its peptidase activity, consequently, to an increase in the level of ubiquitinated proteins and cell death signs. The inhibition of the 26S proteasome stimulated the expression of heat-inducible genes, including transcription factor HSFA2, in the plant and mammals cells. The involvement of HSP90 in the regulation of signal transduction via HSFA2 activation was demonstrated in several plant species, including tomatoes (Hahn et al. 2011). We have shown that in tomatoes, the levels of HSFA2 were rather low in leaves of uninfected tomato plants. The amounts of HSFA2 greatly increased upon heat stress in uninfected tissues, and much less in TYLCV-infected leaves. The inhibition of HSP90 activity caused an additional increase in HSFA2 expression. Subsequent TYLCV infection reduced HSFA2 levels as well as the expression levels of HsfB1, Hsp17, Apx1, and Apx2 (Moshe et al. 2016). TYLCV infection (represented as virions and viral DNA) suppresses HSP90-dependent 26S proteasome inactivation, cell death and HSFA2 signal transduction pathways, resulted in wealthy growth and yielding of tomatoes