The Arabidopsis Tandem Zinc Finger 9 Protein Binds RNA and Mediates Pathogen-Associated Molecular Pattern-Triggered Immune Responses

Abstract

Recognition of pathogen-associated molecular patterns (PAMPs) induces multiple defense mechanisms to limit pathogen growth. Here, we show that the Arabidopsis thaliana tandem zinc finger protein 9 (TZF9) is phosphorylated by PAMP-responsive mitogen-activated protein kinases (MAPKs) and is required to trigger a full PAMP-triggered immune response. Analysis of a tzf9 mutant revealed attenuation in specific PAMP-triggered reactions such as reactive oxygen species accumulation, MAPK activation and, partially, the expression of several PAMP-responsive genes. In accordance with these weaker PAMP-triggered responses, tzf9 mutant plants exhibit enhanced susceptibility to virulent Pseudomonas syringae pv. tomato DC3000. Visualization of TZF9 localization by fusion to green fluorescent protein revealed cytoplasmic foci that co-localize with marker proteins of processing bodies (P-bodies). This localization pattern is affected by inhibitor treatments that limit mRNA availability (such as cycloheximide or actinomycin D) or block nuclear export (leptomycin B). Coupled with its ability to bind the ribohomopolymers poly(rU) and poly(rG), these results suggest involvement of TZF9 in post-transcriptional regulation, such as mRNA processing or storage pathways, to regulate plant innate immunity.

Transcriptomics Analysis of Apple Leaves in Response to Alternaria alternata Apple Pathotype Infection

“…In plants, WRKY (Pandey and Somssich, 2009), Hsf (Pajerowska-Mukhtar et al, 2012), zinc finger protein (Maldonado-Bonilla et al, 2013), ZIP (Dezar et al, 2011), and NAC (Sun et al, 2013) are all important regulators of plant defense responses. The results of our experiment show that almost all WRKYs, ZIPs, Hsfs , and NACs , as well as most MYBs and a portion of the genes encoding for zinc finger proteins were significantly up-regulated.…”

From Chaos to Harmony: Responses and Signaling upon Microbial Pattern Recognition

“…For instance, MPK3 and MPK6 phosphorylate and activate 1-aminocyclopropane-1-carboxylic acid synthase 2 (ACS2) and ACS6, the rate-limiting enzymes in ET biosynthesis, to regulate flg22-triggered ET production (97). In addition, flg22-activated MPK3 and MPK6 phosphorylate tandem zinc finger protein 9 (TZF9), residing in cytoplasmic processing (P) bodies, the sites for mRNA storage and decay, for full PTI responses (107). Flg22-activated MPK4 phosphorylates PAT1, a key component in mRNA decay, leading to its accumulation in P-bodies and contributing to posttranscriptional regulation of gene expression (132).…”

Composition and function of P bodies in Arabidopsis thaliana

“…Transient expression in protoplasts revealed all of them localize to cytoplasmic foci, and the co-localization with PB and SG markers has been demonstrated for specific members (Pomeranz et al, 2010a,b; Bogamuwa and Jang, 2013; Maldonado-Bonilla et al, 2014). …”

“…Once in cytoplasm, TZF1 has potential to be incorporated in PB or SG, though the signals, factors or functional domains of TZF1 that promote assembly in PB are still unknown. The localization of TZF9 is also affected by LMB in Arabidopsis protoplasts, however, further experiments has to be performed in order to confirm the nucleocytoplasmic shuttling (Maldonado-Bonilla et al, 2014). The nucleocytoplasmic shuttling of TZF proteins might indicate they have different functions both in nucleus and cytoplasm, or perhaps, that the proteins recognize the potential mRNA target during or after transcription.…”

“…In vitro evidences indicate that TZF proteins bind to RNA, DNA, or even possess ribonuclease activity (Pomeranz et al, 2010a; Blanvillain et al, 2011; Lee et al, 2012; Maldonado-Bonilla et al, 2014). Directs mRNA targets of Arabidopsis TZF proteins have not been reported so far, and critical amino acid substitutions in the zinc finger motifs might entail their inability to recognize the class II ARE sequence.…”