Abstract
Programmed cell death (PCD) plays a pivotal role in plant development and defense. To investigate the interaction between PCD and R gene-mediated defense, we used the 22K Barley1 GeneChip to compare and contrast time-course expression profiles of Blumeria graminis f. sp hordei (Bgh) challenged barley (Hordeum vulgare) cultivar C.I. 16151 (harboring the Mla6 powdery mildew resistance allele) and its fast neutron-derived Bgh-induced tip cell death1 mutant, bcd1. Mixed linear model analysis identified genes associated with the cell death phenotype as opposed to R gene-mediated resistance. One-hundred fifty genes were found at the threshold P value < 0.0001 and a false discovery rate <0.6%. Of these, 124 were constitutively overexpressed in the bcd1 mutant. Gene Ontology and rice (Oryza sativa) alignment-based annotation indicated that 68 of the 124 overexpressed genes encode ribosomal proteins. A deletion harboring six genes on chromosome 5H cosegregates with bcd1-specified cell death and is associated with misprocessing of rRNAs but segregates independent of R gene-mediated resistance. Barley stripe mosaic virus-induced gene silencing of one of the six deleted genes, RRP46 (rRNA-processing protein 46), phenocopied bcd1-mediated tip cell death. These findings suggest that RRP46, a critical component of the exosome core, mediates RNA processing and degradation involved in cell death initiation as a result of attempted penetration by Bgh during the barley-powdery mildew interaction but is independent of gene-for-gene resistance.
Highlights
Programmed cell death (PCD) is regulated by several diverse pathways in plants
Mutant Characterization and Experimental Design. Mutants isolated for their pathogen-induced cell death provide an initial look at the cellular processes underlying crosstalk of cell death–mediated pathways (Lorrain et al, 2003; Love et al, 2008)
We used the bcd1 mutant, selected from a group of fast neutron–derived C.I. 16151 mutants, where bcd1 was identified by the developing tip cell death upon Blumeria graminis f. sp hordei (Bgh) inoculation while retaining resistant or susceptible responses to avirulent or virulent isolates, respectively (Figure 1)
Summary
Programmed cell death (PCD) is regulated by several diverse pathways in plants. In the interaction between host plants and their pathogens, cell death occurs in both incompatible and compatible responses. It is normally believed that, in the incompatible response, HR is activated by the R-AVR interaction, which restricts pathogen ingress, whereas compatibility triggered cell death may facilitate pathogen infection (Kim and Palukaitis, 1997; Greenberg et al, 2000). Genetic investigations in oat (Avena sativa) revealed that Rds and Rih mediate HR, they act independent of genefor-gene resistance to the oat crown rust pathogen Puccinia coronata f. The dnd mutants exhibit increased broad-spectrum resistance as a result of the activation of multiple defense pathways, none of which are required for the reduced HR (Genger et al, 2008). Diverse pathways mediate cell death and each may have roles or control different aspects of plant–pathogen interactions
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