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Summary: High‐density genetic map is a valuable tool for exploring novel genomic information, quantitative trait locus (QTL) mapping and gene discovery of economically agronomic traits in plant species. However, high‐resolution genetic map applied to tag QTLs associated with important traits and to investigate genomic features underlying recombination landscape in radish (Raphanus sativus) remains largely unexplored. In this study, an ultra‐high‐density genetic map with 378 738 SNPs covering 1306.8 cM in nine radish linkage groups (LGs) was developed by a whole‐genome sequencing‐based approach. A total of 18 QTLs for 11 horticulture traits were detected. The map‐based cloning data indicated that the R2R3‐MYB transcription factor RsMYB90 was a crucial candidate gene determining the taproot skin colour. Comparative genomics analysis among radish, Brassica rapa and B. oleracea genome revealed several genomic rearrangements existed in the radish genome. The highly uneven distribution of recombination was observed across the nine radish chromosomes. Totally, 504 recombination hot regions (RHRs) were enriched near gene promoters and terminators. The recombination rate in RHRs was positively correlated with the density of SNPs and gene, and GC content, respectively. Functional annotation indicated that genes within RHRs were mainly involved in metabolic process and binding. Three QTLs for three traits were found in the RHRs. The results provide novel insights into the radish genome evolution and recombination landscape, and facilitate the development of effective strategies for molecular breeding by targeting and dissecting important traits in radish. [ABSTRACT FROM AUTHOR]

A senescence-induced gene named CsNRT1.7 was cloned from a cucumber cultivar with high capacity for low-N tolerance using a homologous cloning technique based on bioinformatics analysis and cucumber genome information. The full-length cDNA of CsNRT1.7 was 1803 bp with an open reading frame encoding 601 amino acids. Homology analysis showed that CsNRT1.7 had high homology (74%) to the Arabidopsis nitrate transporter gene NRT1.7. Phylogenetic analysis indicated that CsNRT1.7 had a close relationship with NRT1.7 among different nitrate transporters in Arabidopsis. Quantitative RT-PCR and CsNRT1.7pro:GUS reporter analysis showed that CsNRT1.7 was a senescence-induced gene, whose transcription was much stronger in old leaf, followed by mature leaf and young leaf of cucumber plants. CsNRT1.7 could also be induced by low-nitrogen treatment. The transient expression of CsNRT1.7:EGFP in onion epidermal cells indicated that CsNRT1.7 was localized in the plasma membrane. Further functional analysis revealed that 35S:CsNRT1.7/nrt1.7-2 transgenic Arabidopsis plants showed lower nitrate content and larger leaf size than nrt1.7-2 T-DNA insertion Arabidopsis plants. These results provide new clues to further understand the function of CsNRT1.7 regarding senescence-regulated low-nitrogen tolerance in cucumber. [ABSTRACT FROM AUTHOR]