| Cucumber（Cucumis sativus L.,2n=14）,the important economic crops,is one of the most widely grown and consumed vegetable crops due to crispy taste,rich nutrition,and diverse eating methods in China.Cucumber fruit shape is composed of fruit length（L）,diameter（D）and its ratio（L/D）,which is an critical factor affecting the appearance quality and commerciality of cucumber,and is affected by multiple quantitative trait loci（QTLs）.At present,although a number of QTLs related to fruit diameter have been located,no genes that controls fruit diameter have been cloned,and the regulation mechanism of cucumber fruit diameter is unknown.In this study,CSSL6-3,a cucumber chromosome segment substitution line,was used to map the cucumber fruit diameter QTL cfd6.3,and the candidate genes in the mapping range were predicted and analyzed.First,we investigated phenotypic variances between cucumber inbred line RNS7 and cucumber chromosome segment substitution line CSSL6-3.Our results showed that the ovary diameter of RNS7 was about 0.85 cm,and the fruit shape index was about 1.3;immature fruit diameter was about 6.5 cm and the fruit index was about 1;the mature fruit had a diameter of10～12 cm and the fruit index was 0.8～1.0.While the ovary diameter of CSSL6-3 was about0.95 cm,the fruit index was about 1.3,the immature fruit diameter was about 5.6 cm,the fruit index was about 1.14 and the mature fruit length diameter was about 9.8 cm,the fruit index was about 1.Our study found that the fruit diameter of immature and mature fruit were significantly smaller than that of RNS7,and the fruit shape index increased significantly compared with RNS7,while the fruit diameter and fruit shape index of the ovary had no difference.Phenotypic identification of the self-pollinated progeny of the CSSL6-3 revealed that the phenotype was consistent with that of CSSL6-3.The fruit diameter of immature and mature fruit were significantly smaller than that of RNS7,and the fruit shape index increased significantly compared with RNS7,while the ovary diameter and fruit shape index had no difference.The results indicated that the phenotype of the CSSL6-3 can be stably inherited.Genetic analysis showed that the phenotype of CSSL6-3 immature fruit with smaller diameter was controlled by a single recessive gene.Microscopic observations showed that compared with RNS7,the cell size of the pericarp and flesh of the fruit cross-section of the CSSL6-3 immature fruit was significantly smaller,and the cell volume of the fruit longitudinal-section was not significantly changed.The volume and number of cells in the transverse and longitudinal sections of the ovary fruit of CSSL6-3 were not significantly different from RNS7,which was consistent with its fruit phenotype.Therefore,the decreased diameter of CSSL6-3 immature fruit is caused by the decreased cell size.Cucumber fruit diameter related QTL cfd6.3 was located in the range of 13.45 Mb～15.61 Mb on chromosome 6,with a physical distance of about 2.16 Mb.Through analysis of candidate genes in the mapping interval,it was found that the Csa6G301060 predicted to encode WUSCHEL-related homeobox（WOX）3 protein.Gene sequencing results showed that there were 13 SNPs in the intron region of CSSL6-3 and RNS7.q RT-PCR results showed that the expression of Csa6G301060 in CSSL6-3 immature fruit was significantly higher than that in RNS7.Therefore,Cs WOX3 may be a candidate gene for regulating fruit diameter in cucumber.The structure and function of Cs WOX3 were analyzed using bioinformatics methods.The results showed that Cs WOX3 encoded 194 amino acids,the molecular formula of the protein was C990H1495N291O294S6,the molecular weight was 22369.89,and the theoretical isoelectric point（PI）was 6.45;the stability coefficient was 74.66,which belonged to the stable protein;the average hydrophilicity（GRAVY）of Cs WOX3 was-0.952,which suggested to be a hydrophilic protein.The Cs WOX3 protein was located in the nucleus,which provided a theoretical basis for its function.In order to clarify the potential function of the WOX gene family in cucumber,our study performed genome-wide identification and analysis of members of the cucumber WOX gene family.The results showed that 11 Cs WOX gene family members containing conserved HD domains.The WOX family members of cucumber were very conservative in structure and evolution and had a high homology with the WOX family members of tomato and Arabidopsis thaliana.Most WOX genes were highly expressed in fruits. |
