TaDIR1-2, a Wheat Ortholog of Lipid Transfer Protein AtDIR1 Contributes to Negative Regulation of Wheat Resistance against Puccinia striiformis f. sp. tritici.

Soyed M Ahmed,Zhensheng Kang,Jia Guo,Jun Guo,Peng Liu,Changan Ji,Tuo Qi,Qinghe Xue

doi:10.3389/fpls.2017.00521

Soyed M Ahmed, Zhensheng Kang + Show 6 more

Open Access

https://doi.org/10.3389/fpls.2017.00521

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Abstract

Very few LTPs have been shown to act through plasma membrane receptors or to be involved in the hypersensitive response (HR). DIR1, a new type of plant LTP interacts with lipids in vitro, moves to distant tissues during systemic acquired resistance (SAR) and therefore is thought to be involved in long-distance signaling during SAR. However, the exact functions of DIR1 orthologs in cereal species under biotic and abiotic stresses have not been thoroughly defined. In this study, a novel wheat ortholog of the DIR1 gene, TaDIR1-2, was isolated from Suwon11, a Chinese cultivar of wheat and functionally characterized. Phylogenetic analysis indicated that TaDIR1-2 is clustered within the nsLTP-Type II group and shows a closer relationship with DIR1 orthologs from monocots than from eudicots. TaDIR1-2 was localized in the cytoplasm and the cell membrane of wheat mesophyll protoplast. Transcription of TaDIR1-2 was detected in wheat roots, stems and leaves. TaDIR1-2 transcript was significantly induced during the compatible interaction of wheat with the stripe rust pathogen, Puccinia striiformis f. sp. tritici (Pst). Treatments with salicylic acid (SA) and low temperature significantly up-regulated the expression of TaDIR1-2. Transient overexpression of TaDIR1-2 did not induce cell death or suppress Bax-induced cell death in tobacco leaves. Knocking down the expression of TaDIR1-2 through virus-induced gene silencing increased wheat resistance to Pst accompanied by HR, increased accumulation of H2O2 and SA, increased expression of TaPR1, TaPR2, TaPAL, and TaNOX, and decreased expression of two reactive oxygen species (ROS) scavenging genes TaCAT and TaSOD. Our results suggest that TaDIR1-2 acts as a negative regulator in wheat resistance to Pst by modulating ROS and/or SA-induced signaling.

Highlights

Plants encounter various unfavorable conditions, such as the lack of nutrients, water, and light or different types of pathogen attack by bacteria, fungi, and viruses (Jones and Dangl, 2006)
To systematically identify Defective in Induced Resistance 1 (DIR1) orthologs from T. aestivum, Aegilops tauschii (A. tauschii) and Triticum urartu (T. urartu), a genome-wide search using DIR1 protein sequences from Arabidopsis and rice as query revealed a total of 25 putative DIR1 loci in wheat (3, 7, and 15 were obtained from the Aegilops tauschii, Triticum urartu and Triticum aestivum genome databases, respectively)
We firstly characterized a AtDIR1 ortholog in wheat, designated TaDIR1-2, and further suggests that it performs a negative role in wheat immunity during the wheat-Puccinia striiformis f. sp. tritici (Pst) interaction

Summary

Introduction

Plants encounter various unfavorable conditions, such as the lack of nutrients, water, and light (abiotic stresses) or different types of pathogen attack by bacteria, fungi, and viruses (biotic stresses) (Jones and Dangl, 2006). Plants lack a vertebrate-like circulatory system and antibodies to protect themselves from pathogen attack; instead plants have developed different types of defense mechanisms, including pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI, formerly called basal resistance), effector-triggered immunity (ETI, formerly termed R gene-mediated resistance), and systemic acquired resistance (SAR) (Staskawicz et al, 1995; Jones and Dangl, 2006). PTI is induced when pattern recognition receptors (PRRs) in the plant recognize conserved microbial factors and confers low-level resistance to virulent pathogens. Effectors that trigger ETI are usually perceived by plant resistance proteins (R proteins), which are conserved intracellular receptors of the nucleotide-binding leucine-rich receptor (NB-LRR) class. ETI induces localized cell death in the infected tissues and can initiate SAR induced by both avirulent and virulent pathogens to immunize systemic tissues against secondary infections by related or unrelated pathogens (Durrant and Dong, 2004)

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