The Chloroplastic Protein THF1 Interacts with the Coiled-Coil Domain of the Disease Resistance Protein N′ and Regulates Light-Dependent Cell Death

Abstract

One branch of plant immunity is mediated through nucleotide-binding/Leu-rich repeat (NB-LRR) family proteins that recognize specific effectors encoded by pathogens. Members of the I2-like family constitute a well-conserved subgroup of NB-LRRs from Solanaceae possessing a coiled-coil (CC) domain at their N termini. We show here that the CC domains of several I2-like proteins are able to induce a hypersensitive response (HR), a form of programmed cell death associated with disease resistance. Using yeast two-hybrid screens, we identified the chloroplastic protein Thylakoid Formation1 (THF1) as an interacting partner for several I2-like CC domains. Co-immunoprecipitations and bimolecular fluorescence complementation assays confirmed that THF1 and I2-like CC domains interact in planta and that these interactions take place in the cytosol. Several HR-inducing I2-like CC domains have a negative effect on the accumulation of THF1, suggesting that the latter is destabilized by active CC domains. To confirm this model, we investigated N9, which recognizes the coat protein of most Tobamoviruses, as a prototypical member of the I2-like family. Transient expression and gene silencing data indicated that THF1 functions as a negative regulator of cell death and that activation of full-length N9 results in the destabilization of THF1. Consistent with the known function of THF1 in maintaining chloroplast homeostasis, we show that the HR induced by N9 is light-dependent. Together, our results define, to our knowledge, novel molecular mechanisms linking light and chloroplasts to the induction of cell death by a subgroup of NB-LRR proteins.

The partial duplication of an E3-ligase gene inTriticeaespecies mediates resistance to powdery mildew fungi

“…According to the model, Thf1 inhibition will lead to disturbed sugar sensing and/or plastid functionality, which have to be postulated as requirements to support obligate biotrophic pathogens such as powdery mildew fungi. The possibility of Thf1 as inhibitor of resistance components such as R-proteins (Hamel et al , 2016) is also included in the model and would be compatible with the observed, rapid HvARM1 TIGS effect on haustorium formation. The role of Thf1 in necrotrophic interactions may be opposite, i.e.…”

“…Toxin A-treatment also triggered an oxidative burst in leaves of wheat and barley (Manning et al , 2010, Manning et al , 2007, Pandelova et al , 2012) thereby providing a link of Thf1 function with ROS control, at least in chloroplasts, and propose a mode of action of Toxin A. Additional support for a relevant role of Thf1 in plant susceptibilty is provided by results showing interaction of the Thf1 protein with the I2-like coiled-coil (CC) domains of several NB LRR-type resistance proteins (Hamel et al , 2016). One of the well-examined members of this group is the N protein mediating resistance in Nicotiana tabaccum against most Tobamoviruses.…”

Impaired expression of chloroplast HSP90C chaperone activates plant defense responses leading to a disease symptom-like phenotype

“…S4). Studies have reported that light-dependent ROS production in chloroplast leads to the HR-like cell death and antiviral resistance (Chandra-Shekara et al ., 2006; Liu et al ., 2007; Chen et al ., 2015; Hamel et al ., 2016). However, the significance of SA in cell death in the present model system needs to be studied further.…”

Genome-wide functional analysis of hot pepper immune receptors reveals an autonomous NLR cluster in seed plants

“…Sensor NLRs in pairs have an additional integrated domain 29 that is unusual and functions in recognizing effector proteins; this domain then relieves the 30 regulation of the executor NLR, resulting in activation of immune responses. The typical 31 NLR pairs are RESISTANCE TO RALSTONIA SOLANACEARUM 1 (RRS1)/RESISTANCE 32 TO PSEUDOMONAS SYRINGAE 4 (RPS4) in Arabidopsis thaliana and RESISTANCE 33 GENE ANALOG 5 (RGA5)/RGA4 in rice (Oryza sativa). These genes are genetically linked 34 and oriented head-to-head so that they may share a promoter for simultaneous regulation of 35 transcription.…”

“…However, G10-381 NLRs are not the only group that contains autoactive CC domains. It was reported that 382 transient overexpression with the tomato or tobacco CC domain of the I2-like NLR induces 383 cell death in N. benthamiana, but this does not occur with the CC domain of pepper I2-like 384 NLRs(31). Interestingly, C-terminal tagging of the CC domain of pepper I2-like NLR with…”