Abstract
The mechanisms of plant defense against pathogen attack in plant leaves have been extensively studied. However, our understanding of plant defense mechanisms in plant roots is still limited. In this study, a semi-dominant mutant nrtp1-D (necrotic root tip 1), with a short-root phenotype, was characterized in rice. Map-based cloning revealed that NRTP1 encoded a typical coiled-coil nucleotide binding leucine rich repeat (CC-NB-LRR) type protein and the mutation caused an amino acid substitution in the Nucleotide-Binding adaptor shared by Apaf1, certain R genes and CED4 (NB-ARC) domain, which may cause constitutive auto-activation of the NRTP1 protein. Gene expression analysis revealed that NRTP1 was preferentially expressed in rice roots. Expression of mutant nrtp1-D in tobacco leaves induced necrotic lesions, which indicated a common mechanism of plant defense response between leaves and roots. Transcriptome analysis revealed that many typical defense-response genes were differentially expressed in homozygous nrtp1-D. In addition, we also found differential expression of genes in pathways which had not previously been described as being associated with pathogen response. Histochemical analysis showed that the level of nitric oxide (NO), but not reactive oxygen species (ROS), was increased in homozygous nrtp1-D mutant roots. These results indicate that, in addition to the mechanism of defense response common to both roots and shoots, a novel pathway may also exist in rice roots, which does not operate in shoots.
Highlights
Rice (Oryza sativa L.) is a model plant for monocotyledonous species, but is the most important staple food, feeding half of the world’s population
In addition to the mechanism of defense response common to both roots and shoots, a novel pathway may exist in rice roots, which is not expressed in shoots
The remaining 130/249 of the progeny exhibited a mild mutant phenotype, with short roots, and the segregation rate among wild type, mild mutant and severe mutant phenotypes is 1:2:1 (P = 0.880). These mild mutants developed reproductive tissues and set seeds, with their offspring segregating in a 1:2:1 ratio (Fig. 1a). These results indicate that the nrtp1-D phenotype segregates as a semi-dominant trait, homozygous mutant plants being seedling lethal
Summary
Rice (Oryza sativa L.) is a model plant for monocotyledonous species, but is the most important staple food, feeding half of the world’s population. Studies of rice defense responses are of great interest for both advancing our mechanistic knowledge of plant-pathogen interaction and for accelerating crop improvement (Chen and Ronald 2011). To overcome the defense responses caused by PTI, some pathogens. The largest family of R proteins is the nucleotide-binding site leucine-rich repeat (NB-LRR) family of proteins (Tameling and Takken 2008). This large family is encoded by hundreds of genes per plant genome, and can be subdivided into two subfamilies: Toll/interleukin-1 receptor (TIR)-NB-LRRs (TNLs) and coiled-coil (CC)-NB-LRRs (CNLs) (McHale et al 2006). The central NB-ARC domain (the nucleotide-binding adaptor shared by Apaf, certain R gene products and CED4) acts as a nucleotide-binding pocket
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