TCP proteins are plant-specific transcription factors widely implicated in leaf morphogenesis and senescence, flowering, lateral branching, hormone crosstalk, and stress responses. However, the relationship between the transcription pattern of TCPs and organ development in cucumber has not been systematically studied. In this study, we performed a genome-wide identification of putative TCP genes and analyzed their chromosomal location, gene structure, conserved motif, and transcript expression. A total of 27 putative TCP genes were identified and characterized in cucumber. All 27 putative CsTCP genes were classified into class I and class II. Class I comprised 12 CsTCPs and Class II contained 15 CsTCPs. The 27 putative CsTCP genes were randomly distributed in five of seven chromosomes in cucumber. Four putative CsTCP genes were found to contain putative miR319 target sites. Quantitative RT-PCR revealed that 27 putative CsTCP genes exhibited different expression patterns in cucumber tissues and floral organ development. Transcript expression and phenotype analysis showed that the putative CsTCP genes responded to temperature and photoperiod and were induced by gibberellin (GA)and ethylene treatment, which suggested that CsTCP genes may regulate the lateral branching by involving in multiple signal pathways. These results lay the foundation for studying the function of cucumber TCP genes in the future.
In cucumber (Cucumis sativus L.), the differentiation and development of female flowers are important processes that directly affect the fruit yield and quality. Sex differentiation is mainly controlled by three ethylene synthase genes, F (CsACS1G), M (CsACS2), and A (CsACS11). Thus, ethylene plays a key role in the sex differentiation in cucumber. The “one-hormone hypothesis” posits that F and M regulate the ethylene levels and initiate female flower development in cucumber. Nonetheless, the precise molecular mechanism of this process remains elusive. To investigate the mechanism by which F and M regulate the sex phenotype, three cucumber near-isogenic lines, namely H34 (FFmmAA, hermaphroditic), G12 (FFMMAA, gynoecious), and M12 (ffMMAA, monoecious), with different F and M loci were generated. The transcriptomic analysis of the apical shoots revealed that the expression of the B-class floral homeotic genes, CsPI (Csa4G358770) and CsAP3 (Csa3G865440), was immensely suppressed in G12 (100% female flowers) but highly expressed in M12 (∼90% male flowers). In contrast, CAG2 (Csa1G467100), which is an AG-like C-class floral homeotic gene, was specifically highly expressed in G12. Thus, the initiation of female flowers is likely to be caused by the downregulation of B-class and upregulation of C-class genes by ethylene production in the floral primordium. Additionally, CsERF31, which was highly expressed in G12, showed temporal and spatial expression patterns similar to those of M and responded to the ethylene-related chemical treatments. The biochemical experiments further demonstrated that CsERF31 could directly bind the promoter of M and promote its expression. Thus, CsERF31 responded to the ethylene signal derived from F and mediated the positive feedback regulation of ethylene by activating M expression, which offers an extended “one-hormone hypothesis” of sex differentiation in cucumber.
Trichomes and fruit spines are important traits that directly affect the appearance quality and commercial value of cucumber. Tril (Trichome-less), an HD-Zip IV transcription factor, plays a crucial role in the initiation of trichomes and fruit spines, but little is known about their exact regulatory mechanisms. In this study, tissue expression pattern analysis indicated that Tril is expressed and functions in the early stage of organ initiation and development. Expression of the Tril gene under the control of its own promoter (the TrilPro::Tril-3*flag fragment) could partly rescue the mutant phenotypes of tril, csgl3 (cucumber glabrous 3, an allelic mutant of tril) and fs1 (few spines 1, a fragment substitution in the Tril promoter region), providing further evidence that Tril is responsible for the initiation of trichomes and fruit spines. In dense spine-type lines, fs1-type lines and different background transgenic lines containing the TrilPro::Tril-3*flag foreign fragment, fruit spine number increased along with the increase in Tril expression, indicating that Tril has a gene dosage effect on fruit spine density in cucumber. The Numerous Spines (NS) gene is a negative regulatory factor of fruit spine density. Characterization of the molecular and genetic interaction between Tril and NS/ns demonstrated that Tril functions upstream of the negative regulator NS with respect to fruit spine initiation. Overall, our results uncover a novel mechanism governing the effect of the Tril gene in regulating fruit spine development and provide a reference for future work on the quality breeding of cucumber.
Next-generation sequencing-aided map-based cloning delimited the cucumber tendril - less1 ( td - 1 ) locus into a 190.7-kb region in chromosome 6 harboring a putative, novel-function candidate gene encoding a histone acetyltransferase ( CsGCN5 ). The tendril initiated from the lateral meristem is an important and characteristic organ for the species in the Cucurbitaceae family including cucumber (Cucumis sativus L.). While the tendril has its evolutionary significance, it also poses a nuisance in cucumber cultivation under protected environments in which tendril-less cucumber has its advantages. From an EMS mutagenesis population, we identified a tendril-less mutant B007, which was controlled by a recessive gene td-1. Through next-generation sequencing-aided map-based cloning, we show CsGCN5 (Cucumis sativus GENERAL CONTROL NONDEREPRESSIBLE 5), a cucumber gene for a histone acetyltransferase as the most possible candidate for td-1. A non-synonymous SNP in the first exon of CsGCN5 resulted in an amino-acid substitution from Asp (D) in the wild type to Asn (N) in the tendril-less mutant. The candidacy of CsGCN5 was further confirmed by multiple lines of evidence in both biparental and natural cucumber populations. Non-significant expression of CsGCN5 in multiple organs was found between the wild type and the mutant. CsGCN5 exhibited strong expression in the tendril of wild-type plants suggesting its important roles in growth and development of plant tendrils. The identification and characterization of the td-1 mutant from the present study provided a useful tool in understanding the molecular mechanisms of tendril organogenesis and investigation of novel functions of the histone acetyltransferase in cucumber.
Cucumber is one of the most important vegetables in the world. The C2H2 zinc finger protein (C2H2-ZFP) family plays an important role in the growth development and abiotic stress responses of plants. However, there have been no systematic studies on cucumber. In this study, we performed a genome-wide study of C2H2-ZFP genes and analyzed their chromosomal location, gene structure, conservation motif, and transcriptional expression. In total, 101 putative cucumber C2H2-ZFP genes were identified and divided into six groups (I–VI). RNA-seq transcriptome data on different organs revealed temporal and spatial expression specificity of the C2H2-ZFP genes. Expression analysis of sixteen selected C2H2-ZFP genes in response to cold, drought, salt, and abscisic acid (ABA) treatments by real-time quantitative polymerase chain reaction showed that C2H2-ZFP genes may be involved in different signaling pathways. These results provide valuable information for studying the function of cucumber C2H2-ZFP genes in the future.
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