ArabidopsisPumilio protein APUM5 suppressesCucumber mosaic virusinfection via direct binding of viral RNAs

Abstract

Posttranscriptional/translational regulation of gene expression is mediated by diverse RNA binding proteins and plays an important role in development and defense processes. Among the RNAbinding proteins, the mammalian Pumilio RNA-binding family (Puf) acts as posttranscriptional and translational repressors. An Arabidopsis Puf mutant, apum5-D, was isolated during a T-DNA insertional mutant screen for mutants with reduced susceptibility to Cucumber mosaic virus (CMV) infection. Interestingly, CMV RNA contained putative Pumilio-homology domain binding motifs in its 3′ untranslated region (UTR) and internal places in its genome. APUM5 directly bound to the 3′ UTR motifs and some internal binding motifs in CMV RNAs in vitro and in vivo. We showed that APUM5 acts as a translational repressor that regulates the 3′ UTR of CMV and affects CMV replication. This study uncovered a unique defense system that Arabidopsis APUM5 specifically regulates CMV infection by the direct binding of CMV RNAs. plant defense | Pumilio RNA binding protein | TuMV P lant viruses are the obligate pathogens, and host proteins facilitate the multiplication of viruses by affecting processes such as viral replication, cell-to-cell movement, and systemic movement of the virus (1). These processes occur upon the interaction between the virus and host proteins or after the suppression of the host basal defense mechanism and often lead to abnormal phenotypes of virus-infected host plants, such as small, highly branched bushes with deformed leaves, stunting, and reduced apical dominance (2-4). Thus, the reduced growth and developmental changes in the virus-infected plants are typical symptoms of virus infection and signify that the virus has undergone a successful life cycle. To understand the molecular mechanisms underlying viral multiplication and symptoms in plants, it is necessary to identify and characterize the host factors involved in these processes.To identify novel host factors involved in the multiplication of plant RNA viruses in susceptible plants, T-DNA insertion mutants of Arabidopsis thaliana Col-0 ecotype, in which CMVKor multiplication is abrogated (5), were screened. An Arabidopsis Puf mutant, apum5-D, in which Cucumber mosaic virus (CMV) multiplication was affected during viral spreading, was isolated. APUM5 contains the Pumilio-homology domain (PHD) and encodes a putative Puf, which was originally identified in Drosophila melanogaster and Caenorhabditis elegans (6). Pufs are highly conserved in various organisms and work as posttranscriptional and translational repressors (7,8). PHD has RNA binding activity; there are eight repeats with three alpha helices in each repeat. The inner surface of the PHD binds the RNA. The outer surface of the domain permits protein-protein interactions with diverse proteins, such as deadenylase and general translation factors (9, 10). Arabidopsis Pufs also exhibit RNA-binding activity and have conserved binding motifs (11,12). However, plant Puf functions have not yet been fully identified or charact...

Carotenogenesis Is Regulated by 5′UTR-Mediated Translation of Phytoene Synthase Splice Variants

“…not located in the cytoplasm or were not reproducibly enriched (Supplemental Data Set S1). The only RNAbinding protein detected was the Pumilio protein APUM5, a posttranscriptional repressor involved in virus defense binding at the 39UTR of target transcripts (Huh et al, 2013). However, overexpression of APUM5 as well as an APUM5 RNAi line showed unchanged AtPSY protein levels compared to the wild type (Supplemental Fig.…”

REDUCED DORMANCY5Encodes a Protein Phosphatase 2C That Is Required for Seed Dormancy inArabidopsis

“…APUM5 was isolated in a mutant screen for reduced susceptibility to Cucumber mosaic virus infection. APUM5 directly binds viral RNAs and works as a negative regulator for Cucumber mosaic virus replication (Huh et al, 2013).…”

Recessive Resistance to Plant Viruses: Potential Resistance Genes Beyond Translation Initiation Factors

“…With several exceptions (Fujisaki and Ishikawa, 2008; Cheng et al, 2009; Huh et al, 2013), many of the host factors characterized so far in plants positively control viral infection; herein, we refer to them as “positive regulators.” These positive regulators have been characterized predominantly through transient knockdown experiments. Knockdown of a gene encoding a positive regulator of viral infection results in a decrease of viral accumulation.…”