Abstract
Disease resistance genes encoding proteins with nucleotide binding sites and Leucine-Rich Repeat (NB-LRR) domains include many members involved in the effector-triggered immunity pathway in plants. The transcript levels of these defense genes are negatively regulated by diverse microRNAs (miRNAs) in angiosperms and gymnosperms. In wheat, using small RNA expression datasets and degradome datasets, we identified five miRNA families targeting NB-LRR defense genes in monocots, some of which arose in the Triticeae species era. These miRNAs regulate different types of NB-LRR genes, most of them with coil-coiled domains, and trigger the generation of secondary small interfering RNAs (siRNA) as a phased pattern in the target site regions. In addition to acting in response to biotic stresses, they are also responsive to abiotic stresses such as heat, drought, salt, and light stress. Their copy number and expression variation in Triticeae suggest a rapid birth and death frequency. Altogether, non-conserved miRNAs as conserved transcriptional regulators in gymnosperms and angiosperms regulating the disease resistance genes displayed quick plasticity including the variations of sequences, gene copy number, functions, and expression level, which accompanied with NB-LRR genes may be tune-regulated to plants in natural environments with various biotic and abiotic stresses.
Highlights
The competition between plants and pathogens has never disappeared, and sometimes, it becomes very intense
MiRNAs have evolved independently in the lineages since a lack of universally conservation among plants and animals [77]. They evolved lots of lineage-specific miRNAs to be involved in the gene regulation networks
Not like the development-associated miRNAs, for the disease resistance-associated miRNAs, there is no common miRNA between eudicots and monocots; the capability of functioning is very similar
Summary
The competition between plants and pathogens has never disappeared, and sometimes, it becomes very intense. The important defense mechanisms include PAMP-Triggered Immunity (PTI) triggered by Pathogen-Associated Molecular Patterns (PAMP) as a preliminary defense [1] and Effector-Triggered. NB-LRRs with a large gene family are an important class of disease resistance genes. Of the total coding genes, 1.19–3.48% were defined as NB-LRR genes in plants [4]. According to their N-terminal features in plants, NB-LRR proteins can be functionally classified into two classes based on the presence of terminal Toll/Interleukin-1 Receptor (TIR) or Coiled-Coil (CC) domains [5]. TIR and CC domains always play a very important role in transmitting signals to cellular targets for effector actions or downstream signaling components [6]. NB-LRR genes have been demonstrated as ancient and conserved genes in plants [7], comparative genomics analysis has shown great structural diversity
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