XopQ induced stromule formation inNicotiana benthamianais causally linked to ETI signaling and depends on ADR1 and NRG1

Abstract

In Nicotiana benthamiana, expression of the Xanthomonas effector XopQ triggers ROQ1-dependent ETI responses and in parallel accumulation of plastids around the nucleus and the formation of stromules. Both processes were proposed to contribute to ETI-related hypersensitive cell death and thereby to plant immunity. Whether these reactions are directly connected to ETI signaling events has not been tested. Here we utilized transient expression experiments to determine whether XopQ-mediated plastid reactions are a result of XopQ perception by ROQ1 or a consequence of XopQ virulence activity. We find that N. benthamiana mutants lacking ROQ1, both RNLs (NRG1 and ADR1) or EDS1, fail to elicit XopQ-dependent host cell death and stromule formation. Mutants lacking only NRG1 lost XopQ-dependent cell death but retained some stromule induction that was abolished in the RNL double mutant. This analysis aligns XopQ-induced stromules with the ETI signaling cascade but not to host programmed cell death. Furthermore, data reveal that XopQ-triggered plastid clustering is not strictly linked to stromule formation during ETI. Our data suggest that stromule formation, in contrast to chloroplast peri-nuclear dynamics, is an integral part of the N. benthamiana ETI response and that both RNL sub-types play a role in this ETI response.

Ubiquitin E3 ligase activity of Ralstonia solanacearum effector RipAW is not essential for induction of plant defense in Nicotiana benthamiana

“…Several following studies also showed that ETI-induced cell death was sometimes segregated from plant immunity (Glocova et al, 2005;Menna et al, 2015;Pitsili et al, 2020;Yang et al, 2022). Recently, the Xanthomonas effector XopQ-triggered immune responses were found to be separated from ETI-induced cell death in N. benthamiana (Prautsch et al, 2023). In the present study, RipAW C177A and RipAW's derivatives triggered plant immunity to restrict bacterial infection without inducing ETI-triggered cell death, which is consistent with these previous studies.…”

EDS1 complexes are not required for PRR responses and execute TNL‐ETI from the nucleus in Nicotiana benthamiana

“…We next tested PTI responses initiated by LRR‐RLK Nb FLS2 in Nb mutant lines deficient in EDS1 complexes or RNLs, including an Nb nrg1 adr1 double mutant (Fig. 1d; Prautsch et al ., 2021). A reduced ROS burst in bak1 plants was not detected when using saturating flg22 concentrations (50 nM; Fig.…”

“…S1 and Table S1. The Nb adr1 nrg1 double mutant line is described in more detail elsewhere (Prautsch et al ., 2021). Nb plants were cultivated in a glasshouse with a 16 h : 8 h, light : dark photoperiod (sunlight and/or IP65 lamps (Philips) equipped with Agro 400 W bulbs (SON‐T); 130–150 μE m −2 s −1 ; switchpoint; 100 μE m −2 s −1 ), 60% relative humidity (RH) at 24°C : 20°C, day : night.…”

Connecting the dots between cell surface- and intracellular-triggered immune pathways in plants

“…Arabidopsis EDS1-PAD4-ADR1 have extensive "basal resistance" functions (weak ETI TNL , bolstering of PTI or yet further distinct function). By contrast, in N. benthamiana, immune functions of EDS1-PAD4 were not detected [47], and ADR1 appears to have a minor role [26,73]. Rather, EDS1-SAG101-NRG1 execute immune functions limited to ETI TNL [47].…”