Comparative study of the leaf transcriptomes and ionoms of Juglans regia and its wild relative species Juglans cathayensis

Juglans regia 'Yuanfeng' is an elite walnut cultivar in China. Juglans cathayensis, a close relative species of Juglans regia originated from China, possesses some superior traits such as strong disease resistance and high fruit number per branch. So far, transcriptomes of either J. regia or J. cathayensis have not been studied and made available to public yet. In the present study, the transcriptomes of J. regia and J. cathayensis leaves were profiled using Illumina HiSeq 2000 platform. A total of 41,914 unigenes were obtained from the combined clean reads of J. regia and J. cathayensis with an average length of 1363 bp and 2529 differentially expressed genes (DEGs) were detected. Gene annotation analyses revealed that 38,483 unigenes (91.81%) were annotated in at least one of the five databases such as Gene Ontology (GO), etc. Meanwhile, the Ca, Mg, Fe, Zn, K and protein contents in the leaves of J. regia and J. cathayensis were compared and significant differences between J. regia and J. cathayensis in terms of the Ca, Mg, Fe and protein contents were discovered. In addition, DEGs associated with the Ca, Mg and Fe content variations between J. regia and J. cathayensis were investigated. Our comparative transcriptomes' analysis between J. regia and J. cathayensis could provide a useful resource for genetic characterization and improvements of J. regia.