An RXLR effector PlAvh142 from Peronophythora litchii triggers plant cell death and contributes to virulence.

Junjian Situ,Yizhen Deng,Wen Li,Zide Jiang,Wensheng Yang,Pinggen Xi,Liqun Jiang,Guanghui Kong,Xiaoning Fan

doi:10.1111/mpp.12905

Abstract

Litchi downy blight, caused by the phytopathogenic oomycete Peronophythora litchii, results in tremendous economic loss in litchi production every year. To successfully colonize the host cell, Phytophthora species secret hundreds of RXLR effectors that interfere with plant immunity and facilitate the infection process. Previous work has already predicted 245 candidate RXLR effector‐encoding genes in P. litchii, 212 of which have been cloned and tested for plant cell death‐inducing activity in this study. We found three such RXLR effectors could trigger plant cell death through transient expression in Nicotiana benthamiana. Further experiments demonstrated that PlAvh142 could induce cell death and immune responses in several plants. We also found that PlAvh142 localized in both the cytoplasm and nucleus of plant cells. The cytoplasmic localization was critical for its cell death‐inducing activity. Moreover, deletion either of the two internal repeats in PlAvh142 abolished the cell death‐inducing activity. Virus‐induced gene silencing assays showed that cell death triggered by PlAvh142 was dependent on the plant transduction components RAR1 (require for Mla12 resistance), SGT1 (suppressor of the G2 allele of skp1) and HSP90 (heat shock protein 90). Finally, knockout of PlAvh142 resulted in significantly attenuated P. litchii virulence on litchi plants, whereas the PlAvh142‐overexpressed mutants were more aggressive. These data indicated that PlAvh142 could be recognized in plant cytoplasm and is an important virulence RXLR effector of P. litchii.

Highlights

In the arms race between plants and microbial plant pathogens, plants develop complex and multilayered immune systems for self-defence: pathogen- or microbe-associated molecular patterns (PAMPs/MAMPs)-triggered immunity (PTI), mediated by pattern recognition receptors (PRRs) and effector-triggered immunity (ETI), mediated by the specific disease resistance (R) proteins that recognize avirulence (AVR) effectors (Chisholm et al, 2006; Jones and Dangl, 2006; Dodds and Rathjen, 2010; Boutrot and Zipfel, 2017; Cesari, 2018; Han, 2018)
Through virus-induced gene silencing (VIGS) assays, we found that cell death triggered by PlAvh142 is dependent on RAR1, SGT1, and HSP90, which suggests that PlAvh142 might be perceived by the innate immune system in plant
Our results show that M2 that lacked the RXLR region was still capable of inducing cell death, while either the IR1 (M3) or IR2 (M4) deletion resulted in loss of the ability to induce cell death in N. benthamiana (Figure 3a)

Summary

| INTRODUCTION

In the arms race between plants and microbial plant pathogens, plants develop complex and multilayered immune systems for self-defence: pathogen- or microbe-associated molecular patterns (PAMPs/MAMPs)-triggered immunity (PTI), mediated by pattern recognition receptors (PRRs) and effector-triggered immunity (ETI), mediated by the specific disease resistance (R) proteins that recognize avirulence (AVR) effectors (Chisholm et al, 2006; Jones and Dangl, 2006; Dodds and Rathjen, 2010; Boutrot and Zipfel, 2017; Cesari, 2018; Han, 2018). Through virus-induced gene silencing (VIGS) assays, we found that cell death triggered by PlAvh142 is dependent on RAR1, SGT1, and HSP90, which suggests that PlAvh142 might be perceived by the innate immune system in plant. To analyse the role of RXLR and IR motifs in cell death-inducing activity, four truncated PlAvh142 variants were constructed and transiently expressed in N. benthamiana (Figure 3a,b). There was no obvious difference in cell death proportion in these silenced plants compared with the control (Figure S2) Taken together, these results show that RAR1, SGT1, and HSP90 are required for the cell death induced by PlAvh142 in N. benthamiana. The overexpressed mutants caused more severe disease symptoms (Figure 7c,d) These results indicate that PlAvh142 contribute to the P. litchii virulence during infection in its native host litchi

| DISCUSSION

Findings

| EXPERIMENTAL PROCEDURES