Superoxide dismutase (SOD) proteins are widely present in the plant kingdom and play important roles in different biological processes. However, little is known about the SOD genes in cucumber. In this study, night SOD genes were identified from cucumber (Cucumis sativus) using bioinformatics-based methods, including 5 Cu/ZnSODs, 3 FeSODs, and 1 MnSOD. Gene structure and motif analysis indicated that most of the SOD genes have relatively conserved exon/intron arrangement and motif composition. Phylogenetic analyses with SODs from cucumber and several other species revealed that these SOD proteins can be traced back to two ancestral SODs before the divergence of monocot and dicot plants. Many cis-elements related to stress responses and plant hormones were found in the promoter sequence of each CsSOD gene. Gene expression analysis revealed that most of the CsSOD genes are expressed in almost all the tested tissues. qRT-PCR analysis of 8 selected CsSOD genes showed that these genes could respond to heat, cold, osmotic, and salt stresses. Our results provide a basis for further functional research on SOD gene family in cucumber and facilitate their potential applications in the genetic improvement of cucumber.

Plant glutathione peroxidases (GPXs) are non-heme thiol peroxidases that play vital roles in maintaining HO homeostasis and regulating plant response to abiotic stress. Here, we performed a comparative genomic analysis of the gene family in cucumber (). As a result, a total of 6 genes were identified, which were unevenly located in four out of the seven chromosomes in cucumber genome. Based on the phylogenetic analysis, the genes of cucumber, Arabidopsis and rice could be classified into five groups. Analysis of the distribution of conserved domains of GPX proteins showed that all these proteins contain three highly conserved motifs, as well as other conserved sequences and residues. Gene structure analysis revealed a conserved exon-intron organization pattern of these genes. Through analyzing the promoter regions of genes, many hormone-, stress-, and development-responsive-elements were identified. Moreover, we also investigated their expression patterns in different tissues and developmental stages as well as in response to abiotic stress and x acid (ABA) treatments. The qRT-PCR results showed that the transcripts of genes varied largely under abiotic stress and ABA treatments at different time points. These results demonstrate that cucumber gene family may function in tissue development and plant stress responses.

Catalase (CAT) is a common antioxidant enzyme in almost all living organisms. Currently, detailed reports on cucumber (Cucumis sativus L.) CAT (CsCAT) genes and tissue expression profiling are limited. In the present study, four candidate CsCAT genes were identified in cucumber. Phylogenetic analysis indicated that CsCAT1-CsCAT3 are closely related to Arabidopsis AtCAT1-AtCAT3, but no obvious counterpart was observed for CsCAT4. Intron/exon structure analysis revealed that only one of the 15 positions was completely conserved. Motif analysis showed that, unlike the CAT genes of other species, none of CsCAT genes contained all 10 motifs. Expression data showed that transcripts of all of the CsCAT genes, except CsCAT4, were detected in five tissues. Moreover, their transcription levels displayed differences under different stress treatments.

YTH domain-containing RNA-binding proteins are involved in post-transcriptional regulation and play important roles in the growth and development as well as abiotic stress responses of plants. However, YTH genes have not been previously studied in cucumber (Cucumis sativus). In this study, a total of five YTH genes (CsYTH1-CsYTH5) were identified in cucumber, which could be mapped on three out of the seven cucumber chromosomes. All CsYTH proteins had highly conserved C-terminal YTH domains, and two of them (CsYTH1 and CsYTH4) harbored extra CCCH and P/Q/N-rich domains. The phylogenesis, conserved motifs and exon-intron structure of YTH genes from cucumber, Arabidopsis and rice were also analyzed. The phylogenetically closely clustered YTHs shared similar gene structures and conserved motifs. An analysis of the cis-acting regulatory elements in the upstream region of these genes resulted in the identification of many cis-elements related to stress, hormone and development. Expression analysis based on the transcriptome data showed that some CsYTHs had development- or tissue-specific expression. In addition, their expression levels were altered under various stresses such as salt, drought, cold, and abscisic acid (ABA) treatments. These findings lay the foundation for the functional analysis of CsYTHs in the future.

Catalase (CAT) is a key scavenging enzyme for the degradation of hydrogen peroxide (H 2 O 2 ) and plays an important role in the tolerance to diverse abiotic stresses in many different organisms. In this study, we characterized the function of a catalase gene (CsCAT3) previously isolated from Cucumis sativus in the defence against a variety of stresses. Protein alignment and phylogenetic analysis revealed that CsCAT3 was clustered in the dicot group and shared 41%-95% identity with other plant CATs. Expression analyses revealed that the expression of CsCAT3 was induced by diverse abiotic stresses such as heat, polyethylene glycol, cold and NaCl treatment, as well as by signalling molecules such as abscisic acid (ABA) and H 2 O 2 . An Escherichia coli heterologous expression system was constructed to characterize the function of CsCAT3 in vitro. Its overexpression in E. coli could increase the tolerance to heat, cold, salinity and osmotic conditions. These results indicate that CsCAT3 plays important roles in abiotic stress tolerance and that CsCAT3 confers tolerance in E. coli recombinants against abiotic stresses, which may be due to the increased activities of antioxidant enzymes that reduce the oxidative damage caused by stress conditions.