The mutation of CsSUN, an IQD family protein, is responsible for the short and fat fruit (sff) in cucumber (Cucumis sativus L.).

The fruit shape of cucumber is an important agronomic trait, and mining regulatory genes, especially dominant ones, is vital for cucumber breeding. In this study, we identified a short and fat fruit mutant, named sff, from an EMS mutagenized population. Compared to the CCMC (WT), sff (MT) exhibited reduced fruit length and increased dimeter. Segregation analysis revealed that the sff phenotype is controlled by a semi-dominant single gene with dosage effects. Through map-based cloning, the SFF locus was narrowed down to a 52.6 kb interval with two SNPs (G651A and C1072T) in the second and third exons of CsaV3_1G039870, which encodes an IQD family protein, CsSUN. The G651A within the IQ domain of CsSUN was identified as the unique SNP among 114 cucumber accessions, and it was the primary cause of the functional alteration in CsSUN. By generating CsSUN knockout lines in cucumber, we confirmed that CsSUN was responsible for sff mutant phenotype. The CsSUN is localized to the plasma membrane. CsSUN exhibited the highest expression in the fruit with lower expression in sff compared to WT. Histological observations suggest that the sff mutant phenotype is due to increased transverse cell division and inhibited longitudinal cell division. Transcriptome analysis revealed that CsSUN significantly affected the expression of genes related to cell division, expansion, and auxin signal transduction. This study unveils CsSUN's crucial role in shaping cucumber fruit and offers novel insights for cucumber breeding.

A mutation in CsGME encoding GDP-mannose 3,5-epimerase results in little and wrinkled leaf in cucumber.

KEY MESSAGE: Map-based cloning revealed that a mutation in a highly conserved amino acid of the CsGME gene encoding GDP-mannose 3,5-epimerase, causes the phenotype of little and wrinkled leaves in cucumbers. Leaf size is a critical determinant of plant architecture in cucumbers, yet only a few genes associated with this trait have been mapped or cloned. Here, we identified and characterized a mutant with little and wrinkled leaves, named lwl-1. Genetic analysis revealed that the phenotype of the lwl-1 was controlled by a single recessive gene. Through map-based cloning, the lwl-1 locus was narrowed down to a 12.22-kb region exclusively containing one fully annotated gene CsGME (CsaV3_2G004170). CsGME encodes GDP-mannose 3,5-epimerase, which is involved in the synthesis of ascorbic acid (ASA) and one of the components of pectin, RG-II. Whole-length sequencing of the 12.22 kb DNA fragment revealed the presence of only a non-synonymous mutation located in the sixth exon of CsGME in lwl-1, resulting in an amino acid alteration from Pro363 to Leu363. This mutation was unique among 118 inbred lines from cucumber natural populations. CsGME expression significantly reduced in various organs of lwl-1, accompanied by a significant decrease in ASA and pectin content in leaves. Both CsGME and Csgme proteins were localized to the cytoplasm. The mutant phenotype exhibited partial recovery after the application of exogenous boric acid. Silencing CsGME in cucumber through VIGS confirmed its role as the causal gene for lwl-1. Transcriptome profiling revealed that CsGME greatly affected the expression of genes related to the cell division process and cell plate formation. This study represents the first report to characterize and clone the CsGME in cucumber, indicating its crucial role in regulating leaf size and development.

A mutation in CsDWF7 gene encoding a delta7 sterol C-5(6) desaturase leads to the phenotype of super compact in cucumber (Cucumis sativus L.).

KEY MESSAGE: A novel super compact mutant, scp-3, was identified using map-based cloning in cucumber. The CsDWF7 gene encoding a delta7 sterol C-5(6) desaturase was the candidate gene of scp-3. Mining dwarf genes is important in understanding stem growth in crops. However, only a small number of dwarf genes have been cloned or characterized. Here, we characterized a cucumber (Cucumis sativus L.) dwarf mutant, super compact 3 (scp-3), which displays shortened internodes and dark green leaves with a wrinkled appearance. The photosynthetic rate of scp-3 is significantly lower than that of the wild type. The dwarf phenotype of scp-3 mutant can be partially rescued by the exogenous brassinolide (BL) application, and the endogenous brassinosteroids (BRs) levels in the scp-3 mutant were significantly lower compared to the wild type. Microscopic examination revealed that the reduced internode length in scp-3 resulted from a decrease in cell size. Genetic analysis showed that the dwarf phenotype of scp-3 was controlled by a single recessive gene. Combined with bulked segregant analysis and map-based cloning strategy, we delimited scp-3 locus into an 82.5 kb region harboring five putative genes, but only one non-synonymous mutation (A to T) was discovered between the mutant and its wild type in this region. This mutation occurred within the second exon of the CsGy4G017510 gene, leading to an amino acid alteration from Leu156 to His156. This gene encodes the CsDWF7 protein, an analog of the Arabidopsis DWF7 protein, which is known to be involved in the biosynthesis of BRs. The CsDWF7 protein was targeted to the cell membrane. In comparison to the wild type, scp-3 exhibited reduced CsDWF7 expression in different tissues. These findings imply that CsDWF7 is essential for both BR biosynthesis as well as growth and development of cucumber plants.

Response of soil microbial community diversity to continuous cucumber cropping in facilities along the Yellow River irrigation area.

Cucumber is an important cash crop; however, continuous cropping obstacles readily occur within the intensive production processes of facility horticulture. This study aimed to determine the effects of continuous cropping on soil quality and the microbial community in the rhizosphere soil of cucumbers. Rhizosphere soil of cucumber planted continuously for 4, 8, and 12 years was investigated, and soil that was not continuously planted was used as the control. Soil physicochemical properties, enzyme activity, microbial diversity, and richness were determined. The results showed that with the increase in continuous cropping years (0, 4, 8, and 12 years), soil total salt content continuously increased, while the pH value significantly decreased. Compared with the control, soil organic matter, alkali-hydrolyzed nitrogen, available phosphorus, available potassium, and nitrate nitrogen contents increased significantly after 4 and 8 years of continuous cropping. Spearman correlation analysis showed that pH was negatively correlated with sucrase or sucrose and available phosphorus was positively correlated with alkaline phosphatase. Compared with the control, the diversity and abundance of bacterial and fungal communities in cucumber rhizosphere soil decreased after 4 and 12 years of continuous cropping. Continuous cropping led to a significant increase in the richness of the dominant phylum of cucumber rhizosphere soil. Principal coordinates analysis showed that, compared with the control, the soil microbial community structure was significantly separated after 4, 8, and 12 years of continuous cropping, and the microbial community structure was most similar after 4 and 8 years of continuous cropping. In addition, redundancy analysis showed that pH was the main driver of soil microbial dominance. In conclusion, continuous cropping of cucumber along the Yellow River irrigation area has led to the deterioration of soil nutrients and microbial communities in that region. This experiment provides a theoretical foundation for addressing the challenges associated with continuous cropping in cucumber cultivation.

A 5.5-kb LTR-retrotransposon insertion inside phytochrome B gene (CsPHYB) results in long hypocotyl and early flowering in cucumber (Cucumis sativus L.).

KEY MESSAGE: The novel spontaneous long hypocotyl and early flowering (lhef) mutation in cucumber is due to a 5551-bp LTR-retrotransposon insertion in CsPHYB gene encoding PHYTOCHROME B, which plays a major role in regulating photomorphogenic hypocotyl growth and flowering. Hypocotyl length and flowering time are important for establishing high-quality seedlings in modern cucumber production, but little is known for the underlying molecular mechanisms of these two traits. In this study, a spontaneous cucumber long hypocotyl and early flowering mutant was identified and characterized. Based on multiple lines of evidence, we show that cucumber phytochrome B (CsPHYB) is the candidate gene for this mutation, and a 5551-bp LTR-retrotransposon insertion in the first exon of CsPHYB was responsible for the mutant phenotypes. Uniqueness of the mutant allele at CsPHYB was verified in 114 natural cucumber lines. Ectopic expression of the CsPHYB in Arabidopsis phyB mutant rescued the long hypocotyl and early flowering phenotype of phyB-9 mutant. The wild-type CsPHYB protein was localized on the membrane and cytoplasm under white light condition, whereas in the nucleus under red light, it is consistent with its roles as a red-light photoreceptor in Arabidopsis. However, the mutant csphyb protein was localized on the membrane and cytoplasm under both white and red-light conditions. Expression dynamics of CsPHYB and several cell elongation-related genes were positively correlated with hypocotyl elongation; the transcription levels of key positive and negative regulators for flowering time were also consistent with the anthesis dates in the mutant and wild-type plants. Yeast two hybrid and bimolecular fluorescence complementation assays identified physical interactions between CsPHYB and phytochrome interacting factor 3/4 (CsPIF3/4). These findings will provide new insights into the roles of the CsPHYB in cucumber hypocotyl growth and flowering time.