Multiple downy mildew effectors target the stress-related NAC transcription factor LsNAC069 in lettuce.

Claudia‐Nicole Meisrimler,Guido Van Den Ackerveken,Bart Oud,Suzan Out,Alexandra J E Pelgrom

doi:10.1111/tpj.14383

Abstract

SummaryTo cause disease in lettuce, the biotrophic oomycete Bremia lactucae secretes potential RxLR effector proteins. Here we report the discovery of an effector‐target hub consisting of four B. lactucae effectors and one lettuce protein target by a yeast‐two‐hybrid (Y2H) screening. Interaction of the lettuce tail‐anchored NAC transcription factor, LsNAC069, with B. lactucae effectors does not require the N‐terminal NAC domain but depends on the C‐terminal region including the transmembrane domain. Furthermore, in Y2H experiments, B. lactucae effectors interact with Arabidopsis and potato tail‐anchored NACs, suggesting that they are conserved effector targets. Transient expression of RxLR effector proteins BLR05 and BLR09 and their target LsNAC069 in planta revealed a predominant localization to the endoplasmic reticulum. Phytophthora capsici culture filtrate and polyethylene glycol treatment induced relocalization to the nucleus of a stabilized LsNAC069 protein, lacking the NAC‐domain (LsNAC069Δ NAC ). Relocalization was significantly reduced in the presence of the Ser/Cys‐protease inhibitor TPCK indicating proteolytic cleavage of LsNAC069 allows for relocalization. Co‐expression of effectors with LsNAC069Δ NAC reduced its nuclear accumulation. Surprisingly, LsNAC069 silenced lettuce lines had decreased LsNAC069 transcript levels but did not show significantly altered susceptibility to B. lactucae. In contrast, LsNAC069 silencing increased resistance to Pseudomonas cichorii bacteria and reduced wilting effects under moderate drought stress, indicating a broad role of LsNAC069 in abiotic and biotic stress responses.

Highlights

Plant pathogenic downy mildews and Phytophthora spp. form a major threat to numerous economically important crops in agriculture
A lettuce NAC transcription factor interacts with four Bremia lactucae effectors Yeast-two-hybrid (Y2H) screens were performed using a lettuce cDNA prey library with the B. lactucae effectors BLN0322-169, BLN0424-147, BLR0522-97, BLR0830-135 and BLR0923-112, that each contain a single C-terminal transmembrane domain (TMD) (Figure 1a) as bait
BLN04, BLR05, BLR08 and BLR09, interacted with the same lettuce target, a NAC transcription factors (TFs) (Lsat_1_v5_gn_6_99960.1, gene identifier used in http:// lgr.genomecenter.ucdavis.edu/; hereafter LsNAC069)

Summary

Introduction

Plant pathogenic downy mildews and Phytophthora spp. form a major threat to numerous economically important crops in agriculture. These filamentous oomycetes penetrate a variety of plant tissues and spread intercellularly through hyphal growth. In the co-evolutionary arms race between plants and pathogens, effector proteins are deployed to suppress plant immune responses. These can be triggered by detection of pathogen-associated molecular patterns (PAMPs) resulting in pattern-triggered immunity (PTI), or effectors leading to effector-triggered immunity. Host-adapted pathogens have evolved effectors to counter both layers of the plant immune system and induce a state of susceptibility (Jones and Dangl, 2006)

Results

Discussion

Conclusion