Characterization and expression analysis of growth regulating factor (GRF) family genes in cucumber

The growth regulating factor (GRF) family is a conserved class of transcription factors involved in various biological processes in plants. However, there have been only a few studies of the GRF family genes in cucumber, Cucumis sativus (Cs). In this study, we identified and characterized 8 CsGRF genes in cucumber. Two highly conserved domains, QLQ and WRC, were identified to be present in all CsGRF proteins. In addition, three less conserved domains (FFD, TQL, and GGPL) were also detected in some CsGRF members. Based on phylogenetic analysis, the GRF genes from cucumber, Arabidopsis, tomato, rice and maize could be classified into 10 groups, and CsGRFs were clustered closer with the GRF genes from dicots (Arabidopsis and tomato) than with those from monocots (rice and maize). Promoter analysis revealed that the CsGRF genes were involved in cucumber growth and development as well as in responses to various hormones and stresses. Transcriptome data showed that the CsGRF genes have distinct expression patterns in different tissues, especially in ovaries and leaves. Expression profiling analysis indicated that all CsGRF genes were responsive to salt and drought stress treatments. These results demonstrate that the cucumber GRF gene family may function in organ development and plant stress responses.