Maize metacaspases modulate the defense response mediated by the NLR protein Rp1‐D21 likely by affecting its subcellular localization

Abstract

SUMMARYPlants usually employ resistance (R) genes to defend against the infection of pathogens, and most R genes encode intracellular nucleotide‐binding, leucine‐rich repeat (NLR) proteins. The recognition between R proteins and their cognate pathogens often triggers a rapid localized cell death at the pathogen infection sites, termed the hypersensitive response (HR). Metacaspases (MCs) belong to a cysteine protease family, structurally related to metazoan caspases. MCs play crucial roles in plant immunity. However, the underlying molecular mechanism and the link between MCs and NLR‐mediated HR are not clear. In this study, we systematically investigated the MC gene family in maize and identified 11 ZmMCs belonging to two types. Further functional analysis showed that the type I ZmMC1 and ZmMC2, but not the type II ZmMC9, suppress the HR‐inducing activity of the autoactive NLR protein Rp1‐D21 and of its N‐terminal coiled‐coil (CCD21) signaling domain when transiently expressed in Nicotiana benthamiana. ZmMC1 and ZmMC2 physically associate with CCD21 in vivo. We further showed that ZmMC1 and ZmMC2, but not ZmMC9, are predominantly localized in a punctate distribution in both N. benthamiana and maize (Zea mays) protoplasts. Furthermore, the co‐expression of ZmMC1 and ZmMC2 with Rp1‐D21 and CCD21 causes their re‐distribution from being uniformly distributed in the nucleocytoplasm to a punctate distribution co‐localizing with ZmMC1 and ZmMC2. We reveal a novel role of plant MCs in modulating the NLR‐mediated defense response and derive a model to explain it.

Multi-Omics Analyses Reveal the Regulatory Network and the Function of ZmUGTs in Maize Defense Response

“…Several studies have used the Rp1-D21 mt to identify genes or loci associated with modulation of the severity of HR (Chintamanani et al, 2010;Chaikam et al, 2011;Olukolu et al, 2014). We have verified that two homolog genes encoding enzymes of lignin biosynthesis pathway ZmHCT1806 and ZmCCoAOMT2 (Wang et al, 2015b;Wang and Balint-Kurti, 2016), two flavone synthase homologs of ZmFNSIs (Zhu et al, 2020), the nicotinate N-methyl transferase ZmNANMT (Liu et al, 2021), and the metacaspase homologs, ZmMC1 and ZmMC2 (Luan et al, 2021), can suppress Rp1-D21-mediated HR likely through physical interaction with the cellular component (CC) signaling domain of Rp1-D21 when transiently expressed in Nicotiana benthamiana. Interestingly, ZmCCoAOMT2 was also proved to confer quantitative resistance to both southern leaf blight and gray leaf spot in maize (Yang et al, 2017).…”

“…Several Rp1-D21 regulators we identified previously interact with CC D21 and suppress CC D21 -mediated HR (Wang et al, 2015b;Wang and Balint-Kurti, 2016;Zhu et al, 2020;Liu et al, 2021;Luan et al, 2021). To investigate whether ZmUGTs can interact with CC D21 , we performed yeast two-hybrid assays.…”

Maize nicotinate N‐methyltransferase interacts with the NLR protein Rp1‐D21 and modulates the hypersensitive response

“…To our knowledge, it has not been reported previously in any species that NA N MTs can play a role in the plant defence response. Although most data were derived from the ectopic system using Agrobacterium ‐mediated transient over‐expression in N. benthamiana , we believe it can largely reflect the situation in the endogenous maize system for the reasons mentioned previously (Luan et al., 2020; Wang, Ji, et al., 2015). We hope to verify these results when maize genetic materials are available in the future.…”

“…We previously reported that both Rp1‐D21 and CC D21 are located in the nucleus and cytoplasm, and that nucleocytoplasmic trafficking plays an important role in auto‐HR induction (Wang & Balint‐Kurti, 2015). We have recently shown that two type I maize metacaspases (ZmMCs), ZmMC1 and ZmMC2, interact with CC D21 and change its subcellular localization to suppress auto‐HR (Luan et al., 2020). When ZmNA N MT was coexpressed with CC D21 in N. benthamiana , it did not cause the redistribution of CC D21 in plant cells (Figure ).…”

“…We have recently shown that two type I maize metacaspases (ZmMCs), ZmMC1 and ZmMC2, interact with CC D21 and change its subcellular localization to suppress auto-HR (Luan et al, 2020).…”