UNUSUAL FLORAL ORGANS (
UFO) was the first identified F-box gene in plants, one that can regulate floral organ development
[37]. Flower development is mainly controlled by
ABC genes, wherein
A genes control the growth of sepals and petals,
B genes control the growth of petals and stamens, and
C genes control the growth of stamens and carpels. The AtUFO can mediate the protein hydrolysis of inhibitors of
APETALA3 (AP3) and
PISTILLATA (PI), class B functional genes, by interacting with
AtASK to promote the expression of
AP3 and
PI [38]. In Arabidopsis, the
Atufo mutation causes a series of floral abnormalities, such as in the number of sepals, flower size, and so on
[37]. Similarly, the
ufo mutation in Cymose
Aquilegia coerulea results in small flowers, increased sepals, and decreased petals and stamens
[39]. In rice, the functions of class B genes
OsMADS4 and
OsMADS16 are largely conservative, being regulated by the F-box gene
DDF1 [40]. Previous studies have also shown that the palea and lemma of
ddf1-1 mutant spikelets were deformed, resulting in untight closure aberrant pistil-like organs. The
OsMADS4 and
OsMADS16 genes were also significantly downregulated, whereas the
DL gene was significantly upregulated in
ddf1-1. This result indicates that
DDF1 can promote
OsMADS4 and
OsMADS16 gene expression and inhibit
DL gene expression. Similarly, the photo-responsive F-box proteinFOF2 adjusts flowering time by promoting the expression of the
FLC gene
[41]. Overexpression of
FOF2 in Arabidopsis can delay flowering, while the dominant-negative mutant results in early flowering. In addition,
FOF2 transgenic plants retained a photoperiod response. Compared with long-day conditions, overexpression of
FOF2 bloomed late under short-day conditions.
HWS can regulate flower and fruit development in addition to the above-mentioned function that controls leaf development
[28]. The sepals of
Arabidopsis thaliana mutant
hws showed fusion, while anther filaments were fused to the side of the silique. Moreover, the siliques of
hws were bigger than WT due to aberrant septum development. Later, it was found that
HWS controlled flower size and floral organ number by regulating the expression of
CUC1 and
CUC2 genes
[42]. Furthermore, the tomato
hws mutants not only cause abnormal flower development but also promote parthenocarpy
[29].