Responses of miRNAs and their target genes to nitrogen- or phosphorus-deficiency in grafted cucumber seedlings

Grafting can improve the growth and abiotic stress tolerance of cucumber. MicroRNAs (miRNAs) play important roles in regulating plant growth and development and in various stress responses. The aim of this study was to investigate the molecular mechanisms of miRNA-mediated responses to nitrogen- (N) and phosphorus- (P) deficiency in grafted cucumber ( Cucumis sativus ). Cucumber scions were grafted onto pumpkin ( Cucurbita moschata ) or C. sativus rootstocks, to yield hetero- and auto-grafted plants, respectively, and the expression of 19 miRNAs and their predicted target mRNAs under N- or P-deficiency were detected by quantitative real-time PCR. Compared with auto-grafted seedlings, hetero-grafted seedlings showed higher expression levels of most miRNAs. In the leaves of hetero-grafted cucumber seedlings, the expression of most miRNAs was increased by 24 and 48 hours of N-deficiency, but decreased by 24 and 48 hours of P-deficiency. In the roots of hetero-grafted seedlings, the expression level of most miRNAs was increased by 24 hours of N-deficiency and 48 hours of P-deficiency. In the leaves of hetero-grafted cucumber seedlings, the expression levels of most of the miRNA-target genes were increased by 24 and 48 hours of N-deficiency, but decreased by 24 and 48 hours of P-deficiency. In the roots, the expression levels of most miRNA-target genes were higher in hetero-grafted seedlings than in auto-grafted seedlings. Under N- or P-deficiency, most target genes showed markedly increased expression levels in the roots of hetero-grafted cucumber seedlings. Our results will be useful for dissecting the miRNA-mediated enhanced tolerance to N- and P-deficiency in grafted cucumber seedlings.