## 3 Genetic and Molecular Regulation Mechanisms of Vegetable Fruit Shape
### Fl  
In vegetable crops, the FL is an important phenotypic trait. Numerous factors affect the FL (Table 1). With FL as a quantitative trait, people have discovered several related loci by Quantitative trait loci (QTLs) mapping, whereas numerous candidate genes related to FL have been discovered (_FS3.2_, _FS3.3_, _f13.2_, _mfl3.2_, _f17.1_, _f4.1_, and _f130.1_) [56; 57; 58; 59]. In addition to the loci, researchers identified a series of genes and regulatory pathways that are involved in vegetable FL. In cucumbers, _short fruit (sf1)_ and _CsFUL1_ can change the FL [60; 61]. [PERSON] et al. identified the _sf3_ mutant in cucumbers and observed a homolog of the _KTN1_ (_CsKTN1_) candidate gene, which encodes a katanin p60 subunit, is associated with the regulation of FL [62].  
In tomatoes, _SUN_, _Ovate family protein (OFP)_, and _Tomeau1-recruiting motif (TRM)_ regulatory factors can affect the FL individually or together. In 2002, [PERSON] et al. identified a pear-shaped fruit regulatory gene _OVATE_ in tomato [63]. OFPs with a conserved OVATE domain play an important role in regulating fruit size. _OFPs_ are plant-specific TFs. Two members of the family, namely, _OVATE_ and _SloFP20_, have been extensively studied in vegetables. The _OVATE_ gene can cause the pear-shaped fruit, and _SIOFP20_ can affect the development of floral organs and pollen tubes by modulating brassinosteroid (BL) and gibberellin (GA) signaling in tomatoes [64]. In _Arabidopsis_, the overexpression of _AtOFP1_ results in a reduced length of floral organ phenotype, which is similar to _OVATE_ and _SIOFP20_ overexpression tomato plants [63; 65]. In the _ovate_ mutant, the cell division pattern of the fruit proximal part changes, the numbers of cells in the proximal and distal directions increase, whereas the number of cells in the middle direction decrease [66]. Additionally, the locus _supressors of OVATE 1 (SOVI)_ can enhance the _OVATE_ mutation [67]. In addition, the overexpression of _Arabidopsis_ OFP homologous genes (_AtOFP13_, _AtOFP15_, _AtOFP16_, and _AtOFP18_) results in a reduced length of siliques [68; 69; 70], these genes are also involved in the regulation of fruit shape, indicating that this family may also control the organ shape in other plants [71]. At present, the molecular mechanism of OVATE is unclear, but it has been shown to interact with microtubule-related proteins, such as TRM [72]. _OVATE_ and _SIOFP20_ interact with the TRM M8 motif through the OFP domain, and the co-expressions of OVATE or SIOFP20 with SITRM3/4 causes the re-localization of OFPs and TRMs from microtubules to the cytoplasm, suggesting that the OFP-TRM protein complex plays a role in cell division and organ growth through a dynamic balance between cytoplasmic and microtubular localizations [73; 74]. In other vegetables, the down-regulation of the _CaOvate_ gene leads to the oblong fruit shape of peppers [75], which indicates that the OFP family is relatively conserved in relation to fruit size [65].  
_SUN_ encodes a protein of the IQ 67 domain (IQD) family, which has a conserved IQD and is involved in the binding of Calmodulin (CaM) [38; 76]. _SUN_ is reported to control the FL and shape in tomatoes, melons, and cucumbers [77; 78; 79; 5; 6; 8; 5; 6; 76; 5; 5; 6; 77; 5;