HSP90s are required for NLR immune receptor accumulation in Arabidopsis

Abstract

SUMMARYHeat shock proteins (HSPs) serve as molecular chaperones for diverse client proteins in many biological processes. In plant immunity, cytosolic HSP90s participate in the assembly, stability control and/or activation of immune receptor complexes. In this paper we report that in addition to the well-established positive roles that HSP90 isoforms play in plant immunity, they are also involved in the negative regulation of immune receptor accumulation. Point mutations in two HSP90 genes, HSP90.2 and HSP90.3, were identified from a forward genetic screen designed to isolate mutants with enhanced disease resistance. We found that specific mutations in HSP90.2 and HSP90.3 lead to heightened accumulation of immune receptors, including SNC1, RPS2 and RPS4. HSP90s may assist SGT1 in the formation of SCF E3 ubiquitin ligase complexes that target immune receptors for degradation. Such regulation is critical for maintaining appropriate levels of immune receptor proteins to avoid autoimmunity.

Mighty Dwarfs: Arabidopsis Autoimmune Mutants and Their Usages in Genetic Dissection of Plant Immunity

“…For example, a genetic screen looking for enhancers of snc1 identified many muse ( mutants, snc1-enhancing ) mutants (Huang et al, 2013). Analysis of the muse mutants lead to the identification of several components involved in proteasome-mediated degradation of SNC1 (Huang S. et al, 2014; Huang Y. et al, 2014; Huang et al, 2016). It also revealed a crucial role of N-terminal acetylation on the turnover of SNC1 (Xu et al, 2015).…”

The HSP90-RAR1-SGT1 based protein interactome in barley and stripe rust

“…In plants, HSP90 and two co-chaperones, RAR1 (required for Mla12 resistance) and SGT1 (suppressor of G-two allele of Skp1), form the 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 HSP90-RAR1-SGT1 (HRS) complex [18,19]. The HRS complex acts as a crucial machinery for stabilizing the nucleotide-binding domain and leucine-rich repeat (NLR) containing proteins [17,20,21], which are a group receptors mediating innate immune responses to microbial pathogens [22,23]. The HSP90 family is a group of highly conserved proteins present in almost all biological species.…”

“…The eventual defense output relies on a variety of crucial elements, such as major resistance genes [10], mitogen-activated protein kinase (MAPK) cascades [11], plant hormones [12,13], and molecular chaperones [14,15]. The heat shock protein 90 (HSP90) is a molecular chaperone required for many cellular processes [16,17]. In plants, HSP90 and two co-chaperones, RAR1 (required for Mla12 resistance) and SGT1 (suppressor of G-two allele of Skp1), form the 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 HSP90-RAR1-SGT1 (HRS) complex [18,19].…”

NLRs in plants

“…Loss of function of SGT1b, a protein associated with SCF complexes, suppresses the reduced accumulation of RPS5 in the rar1 mutant and also causes increased accumulation of SNC1 [53,54]. In addition, loss of function of the SGT1-interacting proteins HSP90 and SRFR1 also results in heightened accumulation of SNC1 and RPS2 [54,55 ]. Although control of NLR turnover by the UPS has only been reported for a small number of plant NLRs, it is likely that many more E3s are involved in NLR degradation considering that plants have highly expanded E3 families.…”