Fruit size and shape are complex traits controlled by many genes and developmental processes, including cell division, cell expansion, and hormone signaling. In melon, fruit length varies enormously across varieties, making it an ideal system for studying fruit morphology. Although previous studies have mapped numerous quantitative trait loci linked to fruit shape, only a small number of causal genes have been functionally validated. This knowledge gap limits the efficiency of breeding programs aiming to optimize fruit appearance and yield. Based on these challenges, it is necessary to conduct in-depth research to identify key regulatory genes and clarify their roles in controlling fruit elongation.

In a study published (DOI: 10.1093/hr/uhaf138) on 21 May 2025 in Horticulture Research, scientists from the Chinese Academy of Agricultural Sciences and collaborating institutions report the identification of a gene called CmFUL1 that plays a central role in controlling melon fruit length. Using genome-wide association studies combined with gene editing and transgenic experiments, the team demonstrates that CmFUL1 functions as a negative regulator of fruit elongation. The work provides both mechanistic insight and practical genetic resources for improving melon varieties through molecular breeding.

The researchers first analyzed genetic and phenotypic data from more than 1,100 diverse melon accessions, allowing them to pinpoint a genomic region on chromosome 12 strongly associated with fruit length and shape. Within this region, CmFUL1, a MADS-box transcription factor, emerged as a leading candidate gene. Expression analyses revealed that CmFUL1 is highly active during flower and ovary development, stages critical for determining final fruit form.

Strikingly, CmFUL1 expression showed a negative correlation with fruit length across different melon varieties: longer fruits consistently displayed lower levels of the gene. To test causality, the team used CRISPR–Cas9 to generate CmFUL1 knockout mutants. These edited plants produced significantly longer fruits, while fruit width remained unchanged, confirming that CmFUL1 specifically restricts elongation.

The researchers further demonstrated that this regulatory role is evolutionarily conserved. When CmFUL1 was overexpressed in tomato, fruits became smaller in both length and width, reinforcing its function as a growth suppressor. Together, these complementary approaches—genetic mapping, expression profiling, genome editing, and cross-species validation—paint a coherent picture of CmFUL1 as a key molecular regulator shaping melon fruit length.

“Our findings show that fruit length is not simply a matter of promoting growth, but also of releasing genetic constraints,” said the study’s corresponding author. “CmFUL1 acts like a built-in limiter during early fruit development. By adjusting its activity, we can achieve substantial changes in fruit shape without disturbing other traits. This kind of precision control is exactly what modern breeding needs, especially as we aim to improve yield, uniformity, and market value simultaneously.”

The discovery of CmFUL1 has direct implications for crop improvement. Because fruit shape strongly influences packaging efficiency, consumer appeal, and yield stability, precise genetic tools for controlling elongation are highly valuable. The identified gene provides a promising target for marker-assisted selection or genome editing in melon breeding programs. Beyond melon, the conserved function of FUL-like genes suggests broader relevance for other fruit crops, including cucumber and tomato. More broadly, the study highlights how integrating population genomics with functional biology can accelerate the translation of genetic discoveries into practical agricultural innovations, supporting more efficient and sustainable food production systems.

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