Abstract
NONEXPRESSOR OF PATHOGENESIS-RELATED GENES 1 (NPR1), and its paralogues NPR3 and NPR4, are bona fide salicylic acid (SA) receptors and play critical regulatory roles in plant immunity. However, comprehensive identification and analysis of the NPR1-like gene family had not been conducted so far in bread wheat and its relatives. Here, a total of 17 NPR genes in Triticum aestivum, five NPR genes in Triticum urartu, 12 NPR genes in Triticum dicoccoides, and six NPR genes in Aegilops tauschii were identified using bioinformatics approaches. Protein properties of these putative NPR1-like genes were also described. Phylogenetic analysis showed that the 40 NPR1-like proteins, together with 40 NPR1-related proteins from other plant species, were clustered into three major clades. The TaNPR1-like genes belonging to the same Arabidopsis subfamilies shared similar exon-intron patterns and protein domain compositions, as well as conserved motifs and amino acid residues. The cis-regulatory elements related to SA were identified in the promoter regions of TaNPR1-like genes. The TaNPR1-like genes were intensively mapped on the chromosomes of homoeologous groups 3, 4, and 5, except TaNPR2-D. Chromosomal distribution and collinearity analysis of NPR1-like genes among bread wheat and its relatives revealed that the evolution of this gene family was more conservative following formation of hexaploid wheat. Transcriptome data analysis indicated that TaNPR1-like genes exhibited tissue/organ-specific expression patterns and some members were induced under biotic stress. These findings lay the foundation for further functional characterization of NPR1-like proteins in bread wheat and its relatives.
Highlights
Bread wheat (Triticum aestivum L.), known as common wheat, is a major grain crop with very high economic value globally
To study the phylogeny of the NONEXPRESSOR OF PATHOGENESIS-RELATED GENES 1 (NPR1)-like family, an unrooted phylogenetic tree was constructed using the sequences of the 40 NPRs, and 4 OsNPRs, 5 PaNPRs, and 31 NPRs obtained through molecular cloning techniques from eight monocots and 15 dicots in the published literature (Table S1)
The results demonstrated that NPR1-like proteins were clustered into three major clades: clade I (AtNPR1/2 subfamily) containing OsNPR1 [50,51,52], BjNPR1 [53], MuNPR1 [54], HvNPR1 [55,56], and NtNPRIn1t
Summary
Bread wheat (Triticum aestivum L.), known as common wheat, is a major grain crop with very high economic value globally. This allohexaploid bread wheat (T. aestivum, 2n = 6x = 42) is comprised of three closely homoeologous chromosome groups (AABBDD), originating from a series of natural hybridization events [1,2]. Diploid Triticum urartu (the A-genome donor) hybridized with an unknown diploid grass (considered probably as Aegilops speltoides, the B-genome donor) to produce tetraploid emmer wheat (Triticum dicoccoides, AABB). Emmer wheat hybridized with diploid goat grass (Aegilops tauschii, the D-genome donor) to form hexaploid wheat around 8000 years ago. Identification and analysis of these essential components involved in SA-dependent defense responses is very important to understand the immune mechanism in bread wheat and its relatives
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