Castanea root transcriptome in response to Phytophthora cinnamomi challenge

The European chestnut, an important forest species for the economy of Southern Europe, covers an area of 2.53 million hectares, including 75,000 ha devoted to fruit production. Castanea sativa is declining due to ink disease caused by Phytophthora cinnamomi. To elucidate chestnut defense mechanisms to ink disease, we compared the root transcriptome of the susceptible species C. sativa and the resistant species C. crenata after P. cinnamomi inoculation. Four cDNA libraries were constructed, two of them included root samples from C. sativa, inoculated and non-inoculated and the other two libraries comprised samples from C. crenata at identical conditions. Pyrosequencing produced 771,030 reads and assembly set up 15,683 contigs for C. sativa and 16,828 for C. crenata. GO annotation revealed terms related to stress as response to stimulus, transcription factor activity or signaling for both transcriptomes. Differential gene expression analysis revealed that C. crenata involved more genes related with biotic stress upon pathogen inoculation than C. sativa. Those genes for both species are involved in regulation of plant immune response and stress adaptation and recovery. Furthermore, it is suggested that both species recognize the pathogen attack; however, the resistant species may involve more genes in the defense response than the susceptible species. RNA-seq enabled the selection of candidate genes for ink disease resistance in Castanea. The present data is a valuable contribution to the available Castanea genomic resources and constitutes the basis for further studies.