R gene expression changes related to Cercospora hydrangeae L.

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Abstract
Nursery growing as well as common landscape hydrangeas are all susceptible to leaf spot fungus Cercospora hydrangeae. Warm and rainy weather causes the fungal spores to germinate quickly and spread over the plant leaves forming small purple or brown spots. Although Hydrangea plants are not killed by leaf spot, it detracts from the value of plants through the reduction of flowering and plant vigor. The aim of our study was to isolate, characterize and investigate the expression profile of Hydrangea macrophylla resistance (R) gene transcripts under C. hydrangeae fungus infection and examine their evolutionary relationships by phylogenetic analysis. R-genes are thought to be one of the components of the genetic resistance in plants and most of them encode nucleotide binding site-leucine rich repeat (NBS–LRR) proteins. A cDNA–NBS strategy was carried out using as template cDNAs isolated from control and infected plant leaves. The cDNA–NBS profiling gave an excellent bands reproducibility. Twenty new transcripts corresponding to NBS–LRR proteins were identified only in infected plants. The extent of positivity between the aminoacid sequences at NBS region varied from 45 to 90 %, which indicates the diversity among the RGAs. The results of this paper will provide a genomic framework for the further isolation of candidate disease resistance NBS-encoding genes in Hortensia, and contribute to the understanding of the evolutionary mode of NBS-encoding genes in Hydrangeaceae crops.

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