Mapping and identification of CsSF4, a gene encoding a UDP-N-acetyl glucosamine-peptide N-acetylglucosaminyltransferase required for fruit elongation in cucumber (Cucumis sativus L.)

The short fruit length phenotype in sf4 is caused by a SNP in Csa1G665390, which encodes an O-linked N-acetylglucosamine (GlcNAc) transferase in cucumber. Cucumber fruit is an excellent resource for studying fruit morphology due to its fast growth rate and naturally abundant morphological variations. The regulatory mechanisms underlying plant organ size and shape are important and fundamental biological questions. In this study, a short-fruit length mutant, sf4, was identified from an ethyl methanesulfonate (EMS) mutagenesis population derived from the North China-type cucumber inbred line WD1. Genetic analysis indicated that the short fruit length phenotype of sf4 was controlled by a recessive nuclear gene. The SF4 locus was located in a 116.7-kb genomic region between the SNP markers GCSNP75 and GCSNP82 on chromosome 1. Genomic and cDNA sequences analysis indicated that a single G to A transition at the last nucleotide of Csa1G665390 intron 21 in sf4 changed the splice site from GT-AG to GT-AA, resulting in a 42-bp deletion in exon 22. Csa1G665390 is presumed to be a candidate gene, CsSF4 that encodes an O-linked N-acetylglucosamine (GlcNAc) transferase (OGT). CsSF4 was highly expressed in the leaves and male flowers of wild-type cucumbers. Transcriptome analysis indicated that sf4 had alterations in expression of many genes involved in hormone response pathways, cell cycle regulation, DNA replication, and cell division, suggesting that cell proliferation-associated gene networks regulate fruit development in cucumber. Identification of CsSF4 will contribute to elucidating the function of OGT in cell proliferation and to understanding fruit elongation mechanisms in cucumber.