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Key message: Transcriptome-based gene expression analysis identifies many critical salt-responsive genes in radish and facilitates further dissecting the molecular mechanism underlying salt stress response. Abstract: Salt stress severely impacts plant growth and development. Radish, a moderately salt-sensitive vegetable crop, has been studied for decades towards the physiological and biochemical performances under salt stress. However, no systematic study on isolation and identification of genes involved in salt stress response has been performed in radish, and the molecular mechanism governing this process is still indistinct. Here, the RNA-Seq technique was applied to analyze the transcriptomic changes on radish roots treated with salt (200 mM NaCl) for 48 h in comparison with those cultured in normal condition. Totally 8709 differentially expressed genes (DEGs) including 3931 up- and 4778 down-regulated genes were identified. Functional annotation analysis indicated that many genes could be involved in several aspects of salt stress response including stress sensing and signal transduction, osmoregulation, ion homeostasis and ROS scavenging. The association analysis of salt-responsive genes and miRNAs exhibited that 36 miRNA-mRNA pairs had negative correlationship in expression trends. Reverse-transcription quantitative PCR (RT-qPCR) analysis revealed that the expression profiles of DEGs were in line with results from the RNA-Seq analysis. Furthermore, the putative model of DEGs and miRNA-mediated gene regulation was proposed to elucidate how radish sensed and responded to salt stress. This study represents the first comprehensive transcriptome-based gene expression profiling under salt stress in radish. The outcomes of this study could facilitate further dissecting the molecular mechanism underlying salt stress response and provide a valuable platform for further genetic improvement of salt tolerance in radish breeding programs. [ABSTRACT FROM AUTHOR]

Simple sequence repeats (SSRs) are highly polymorphic and co-dominant markers, providing an important genomic resource for genetic research. Recently, large-scale transcriptome sequencing has become a reliable and efficient approach for the identification and development of new genic-SSR markers and has been successfully conducted in a few important plant species. However, SSR development based on transcriptome sequencing remains limited in radish ( Raphanus sativus L.). In the present study, from a total of 73,084 unigenes and 150,455 contigs which were assembled from 71.95 million Illumina sequence reads of a radish taproot library, a collection of 11,928 genic-SSR loci were successfully identified in 11,311 unigene sequences. Trinucleotide repeats were the most abundant repeat units, as in many other plants, with a frequency of 52 %. Furthermore, a total of 5,503 genic-SSR primers were developed, from which 1,052 SSR primers were synthesized, and a subset of 823 (78.23 %) primers could generate stable bands. Moreover, 67 selected informative genic-SSR markers were used to determine the genetic diversity of 32 radish genotypes, in which the polymorphism information content values ranged from 0.49 to 0.89. For effective cultivar identification, a novel strategy called manual cultivar identification diagram was employed. Thirty-two radish accessions were clearly separated by six genic-SSR markers. Additionally, the cross-species/genera transferability of these SSRs was further validated in nine relatives in Brassicaceae. These results suggested that the novel genic-SSR markers, as a basis for future genetic linkage and gene tagging analysis, could be very valuable in facilitating genetic mapping, marker-assisted selection and comparative genome analysis. [ABSTRACT FROM AUTHOR]