Pm21 CC domain activity modulated by intramolecular interactions is implicated in cell death and disease resistance

Abstract

Molecular Plant Pathology. 2020;21:975-984. | 975 wileyonlinelibrary.com/journal/mpp | INTRODUC TI ONPlants prevent pathogen invasion via a two-layered immune system (Dodds and Rathjen, 2010;Dangl et al., 2013). The first layer is pattern-triggered immunity (PTI) governed by membrane-localized pattern recognition receptors (PRRs). PTI is the basal immune response of plants against infections by pathogens (Couto and Zipfel, 2016;Tang et al., 2017). Once pathogens suppress PTI and enter host cells, plants employ the second layer of the immune system to combat pathogens.In this branch of the immune system, intracellular nucleotide-binding Abstract Nucleotide-binding (NB) leucine-rich repeat (LRR) receptors (NLRs) provide resistance against several plant pathogens. We previously cloned the wheat powdery mildew resistance gene Pm21, which encodes a coiled-coil (CC) NLR that confers broad-spectrum resistance against Blumeria graminis f. sp. tritici. Here, we report comprehensive biochemical and functional analyses of Pm21 CC domain in Nicotiana benthamiana. Transient overexpression assay suggested that only the extended CC (eCC, amino acid residues 1-159) domain has cell-death-inducing activity, whereas the CC-containing truncations, including CC-NB and CC-NB-LRR, do not induce celldeath responses. Coimmunoprecipitation (Co-IP) assay showed that the eCC domain self-associates and interacts with the NB and LRR domains in planta. These results imply that the activity of the eCC domain is inhibited by the intramolecular interactions of different domains in the absence of pathogens. We found that the LRR domain plays a crucial role in D491V-mediated full-length (FL) Pm21 autoactivation. Some mutations in the CC domain leading to the loss of Pm21 resistance to powdery mildew impaired the CC activity of cell-death induction. Two mutations (R73Q and E80K) interfered with D491V-mediated Pm21 autoactivation without affecting the cell-death-inducing activity of the eCC domain. Notably, some susceptible mutants harbouring mutations in the CC domain still exhibited cell-death-inducing activity. Taken together, these results implicate the CC domain of Pm21 in cell-death signalling and disease-resistance signalling, which are potentially independent of each other. K E Y W O R D S CC domain, cell death, disease resistance, intramolecular interaction, Pm21 S U PP O RTI N G I N FO R M ATI O N Additional supporting information may be found online in the Supporting Information section. How to cite this article: Gao A, Hu M, Gong Y, et al. Pm21 CC domain activity modulated by intramolecular interactions is implicated in cell death and disease resistance. Molecular Plant Pathology. 2020;21:975-984.

Genetic Mapping of Powdery Mildew Resistance Genes in Wheat Landrace ‘Guizi 1’ Using Genotyping-By-Sequencing

“…However, Pm21 originated from the 6AL•6VS translocation of H. villosa. Additionally, wheat varieties carrying Pm21 are reportedly immune and/or highly resistant to the Bgt isolates [21,50]. The many years of eld observations have indicated that GZ1 has a moderate and stable resistance to powdery mildew.…”

“…Serine and threonine protein kinase genes (including Stpk-V, DvMPK1, DvMLPK, DvUPK, and DvPSYR1) have been located to the Pm21 locus and appear to be required for Pm21-mediated resistance to wheat powdery mildew [17,18]. Recently, the Pm21 gene was cloned and con rmed to encode a single coiled-coil, nucleotide-binding site, leucine-rich repeat protein, in which the coiled-coil domain's activity was closely related to Pm21 resistance to powdery mildew [19][20][21]. Pm56, which resulted from the 6AL•6RS translocation of Secale cereale L. was mapped to the subtelomere region of the arm [14].…”

Diversity, structure and function of the coiled‐coil domains of plant NLR immune receptors

“…In addition, longer fragment containing further extended sequences outside CC domains may block CC function. In the case of Pm21 (Gao et al, 2020) and Tm‐2 2 (Wang et al, 2020), the CC domain can induce cell death, although the longer CC‐NB‐ARC does not. Interestingly, the converse is true for RPS5, as the CC‐NB‐ARC activates cell death instead of the CC domain (Ade et al, 2007).…”

“…Isolated CC domains (Collier et al, 2011; Maekawa et al, 2011; Wang et al, 2015c; Casey et al, 2016; Cesari et al, 2016; Baudin et al, 2017; Kim et al, 2018; Wroblewski et al, 2018; Maekawa et al, 2019; Gao et al, 2020; Wang et al, 2020) and TIR domains (Frost et al, 2004; Swiderski et al, 2009; Krasileva et al, 2010; Bernoux et al, 2011; Williams et al, 2014; Schreiber et al, 2016) from some NLRs can initiate cell death signaling on their own, suggesting that some CC and TIR domains mediate the initiation of immune signaling following NLR activation.…”

Diversity and similarity of wheat powdery mildew resistance among three allelic functional genes at the Pm60 locus

“…Pm38 and Pm46 are ABC and hexose transporters, respectively. Pm1a , Pm2 , Pm3 / Pm8 / Pm17 , Pm5e , Pm21 , Pm41 , and Pm60 encode immune receptor CNL proteins with nucleotide‐binding sites (NBS) and leucine‐rich repeat (LRR) domains associated with coiled‐coils at the N ‐termini (Gao et al., 2020; Hewitt et al., 2021; Hurni et al., 2013; Li et al., 2020; Sanchez‐Martin et al., 2016; Sánchez‐Martín & Keller, 2021; Singh et al., 2018; Xie et al., 2020; Yahiaoui et al., 2004, 2009; Zou et al., 2018).…”