Fine Mapping And Functional Verification Of The Major-effect QTL Fnl7.1 For Fruit Neck Length In Cucumber

Fruit neck length(FNL) is an important quality trait in cucumber because it directly affects its market value.However,its genetic basis remains largely unknown.In present study,the cucumber line YN(male parent,P1)and Jin5-508(female parent,P2)that showed extreme FNL were selected to construct F2 segregated populations.The mixed major gene plus polygene inheritance model was used to analyze the FL and FNL phenotype in the six generations(P1,P2,F1,B1,B2 and F2).The major-effect QTL controlling FNL was identified by QTL-seq,and narrowed down by fine genetic mapping;Through whole-genome sequencing,SNP haplotyping and fine genetic mapping.qRT-PCR technology was used to verify the function of candidate genes,and transgenic technology was used to further verify the function of candidate genes.The main results are as follows1?A quantitative trait locus(QTL) on chromosome 7,Fnl7.1,was identified through a genome-wide comparison of single nucleotide polymorphisms between long-and short-FNL F2 pools,and it was confirmed by traditional QTL mapping in multiple environments.2?The fnl7.1 was finally narrowed down to a 25.43kb region containing 4 genes(Csa7G388330?Csa7G388340?Csa7G388350?Csa7G38836).Their predictive functions are respectively:Late embryogenesis abundant protein,Ethylene receptor,Uncharacterized protein,Acyl-CoA N-acyltransferase with RING/FYVE/PHD-type zinc finger protein.Our findings shed light on the genetic architecture underlying FNL phenotype in cucumber,and provide a list of potential gene targets for further elucidating.3?The results of QRT PCR showed that only Csa7G388330(CSFnl7.1)showed regularity among parents at different developmental stages,and a tissue-specific expression analysis revealed that CsFnl7.1 w as expressed in all 10 tested tissues(root,stem,leave,petiole,tendril,male flowers,female flowers,neck,flesh and peel),with the highest expression occurring in neck.These data further suggested that CsFnl7.1 is a good candidate for the Fnl7.1 locus.4?Regional association analysis,sequences alignment and gene expression analysis revealed that CsFnl7.1 was the most likely candidate Fnl7.1 locus,which encodes a late embryogenesis abundant protein.5?The increased expression of CsFnl7.1 in long-necked Jin5-508 may be attributed to mutations in the promoter region upstream of the gene body.The function of CsFnl7.1 in FNL control was confirmed by its overexpression in transgenic cucumbers.