Abstract
Kiwifruit bacterial canker, caused by the bacterial pathogen Pseudomonas syringae pv. actinidiae (Psa), is a destructive disease in the kiwifruit industry globally. Consequently, understanding the mechanism of defense against pathogens in kiwifruit could facilitate the development of effective novel protection strategies. The Non-expressor of Pathogenesis-Related genes 1 (NPR1) is a critical component of the salicylic acid (SA)-dependent signaling pathway. Here, a novel kiwifruit NPR1-like gene, designated AeNPR1a, was isolated by using PCR and rapid amplification of cDNA ends techniques. The full-length cDNA consisted of 1952 base pairs with a 1,746-bp open-reading frame encoding a 582 amino acid protein. Homology analysis showed that the AeNPR1a protein is significantly similar to the VvNPR1 of grape. A 2.0 Kb 5′-flanking region of AeNPR1a was isolated, and sequence identification revealed the presence of several putative cis-regulatory elements, including basic elements, defense and stress response elements, and binding sites for WRKY transcription factors. Real-time quantitative PCR results demonstrated that AeNPR1a had different expression patterns in various tissues, and its transcription could be induced by phytohormone treatment and Psa inoculation. The yeast two-hybrid assay revealed that AeNPR1a interacts with AeTGA2. Constitutive expression of AeNPR1a induced the expression of pathogenesis-related gene in transgenic tobacco plants and enhanced tolerance to bacterial pathogens. In addition, AeNPR1a expression could restore basal resistance to Pseudomonas syringae pv. tomato DC3000 (Pst) in Arabidopsis npr1-1 mutant. Our data suggest that AeNPR1a gene is likely to play a pivotal role in defense responses in kiwifruit.
Highlights
Kiwifruit (Actinidia spp) is a perennial deciduous vine originating from China, and it is an emerging economic fruit tree
Hongyang) and Actinidia deliciosa (i.e., Hayward) cultivars and their pollinators are highly susceptible to the infection of kiwifruit bacterial canker, a major kiwifruit disease caused by Pseudomonas syringae pv. actinidiae (Psa)
Alignment of the deduced amino acid sequence revealed that AeNPR1a is most closely related to AcNPR1a (98.11% identity), which originates from the same genus, with only 10 residues varying, followed by VvNPR1 (74.06% identity), StNPR1 (73.21% identity), NtNPR1 (71.94% identity), and AtNPR1 (52.86% identity) (Figure 1)
Summary
Kiwifruit (Actinidia spp) is a perennial deciduous vine originating from China, and it is an emerging economic fruit tree. It has long been called “the king of VC” because of its unique flavor and high nutrient composition, being rich in vitamin C (Huang et al, 2013; Huang, 2016). A comprehensive understanding of kiwifruit disease defense mechanisms would facilitate the management and decrease of the effects of pathogen infection and the development of effective strategies for controlling Psa. In recent years, the genomes of several kiwifruit cultivars (i.e., A. chinensis Hongyang, Red, and A. eriantha White) have been sequenced, which is convenient for the exploration of genes involved in defense responses and the study of regulatory mechanisms (Huang et al, 2013; Pilkington et al, 2018; Tang et al, 2019)
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