Dongming Liu

Plant architecture is a critical agronomic trait in watermelon (Citrullus lanatus), with vine length directly influencing planting density, light interception, and field management efficiency. Short-vine forms have become important agronomic targets in breeding due to their advantages of high-density planting, efficient light utilization, and simplified field management. In this study, a dwarf mutant, designated PKH207, was identified from an ethyl methanesulfonate (EMS)-mutagenized population of the watermelon inbred line G42. The mutant exhibited significantly reduced plant height and shortened internodes due to decreased cell expansion in stem tissues. Genetic analysis indicated that the dwarf phenotype in PKH207 is controlled by a single recessive gene, which was named Cldw2 (Citrullus lanatus dwarf mutant 2). Using a population of 558 F₂ plants, bulked segregant analysis sequencing (BSA-seq) and linkage mapping delimited the causal locus to a 540.6 kb region on chromosome 10. Within this interval, a single-nucleotide polymorphism (SNP) mutation was identified in the gene ClG42_10g0100600, encoding an α-tubulin, and this gene was determined to be the candidate gene for the dwarf phenotype. Transcriptome analysis revealed that this mutation significantly disrupts key biological processes, including cell wall biosynthesis, microtubule cytoskeleton organization, and auxin signaling pathways, contributing to the dwarfism phenotype. This study identifies a novel dwarfing allele in cucurbits and provides a direct molecular target for breeding compact watermelon cultivars suited to high-density production.

Watermelon is an economically important horticultural crop cultivated worldwide. The ERF family is one of the largest transcription factor families in plan

Watermelon (Citrullus lanatus) and melon (Cucumis melo) are globally important cucurbit crops, with China being the largest producer and consumer. Traditional breeding methods face difficulties in significantly improving yield and quality. Smart breeding, which combines genomics, gene editing, and artificial intelligence (AI), holds great promise but fundamentally depends on understanding the molecular mechanisms controlling important agronomic traits. This review summarizes the progress made over recent decades in discovering and understanding the functions of genes that control essential traits in watermelon and melon, focusing on plant architecture, fruit quality, and disease resistance. However, major challenges remain: relatively few genes have been fully validated, the complex gene networks are not fully unraveled, and technical hurdles like low genetic transformation efficiency and difficulties in large-scale trait phenotyping limit progress. To overcome these and enable the development of superior new varieties, future research priorities should focus on the following: (1) systematic discovery of genes using comprehensive genome collections (pan-genomes) and multi-level data analysis (multi-omics); (2) deepening the study of gene functions and interactions using advanced gene editing and epigenetics; (3) faster integration of molecular knowledge into smart breeding systems; (4) solving the problems of genetic transformation and enabling efficient large-scale trait and genetic data collection (high-throughput phenotyping and genotyping).

The early flowering and less lateral branches in watermelon hold significant agricultural value. The synergistic effects of these traits provide an ideal template for watermelon plant architecture improvement. However, the molecular regulatory networks underlying the development of lateral organs (including branches and flowers) in watermelon remain unclear. In this study, we found ClTFL1 knockout lines significantly promote flowering time and inhibit lateral branching and tendril formation, while also leading to a mild apical flower phenotype. These findings indicate that the function of ClTFL1 in watermelon is more extensive than that of its homologous genes in Arabidopsis, rice, and tomato. Through yeast two-hybrid screening, we identified the interacting proteins of ClTFL1, including members of the 14-3-3 family ClGRF8, ClGRF9, and ClGRF12. Bimolecular fluorescence complementation (BiFC) assays further demonstrated ClTFL1 could directly interact with the ClGRF8, ClGRF9, and ClGRF12 protein. The knockout of ClGRF8 and ClGRF12 leads to reduced lateral branches and early flowering. These phenotypes are highly consistent with those of ClTFL1 knockout mutants. Our findings demonstrate the important role of the ClTFL1-ClGRFs module in regulating lateral organ development and flowering time in watermelon, offering important targets for watermelon plant architectural modification and molecular breeding.

Rind pattern is one of the most important appearance qualities of watermelon, and the mining of different genes controlling rind pattern can enrich the variety of consumer choices. In this study, a unique intermittent rind stripe was identified in the inbred watermelon line WT20. The WT20 was crossed with a green stripe inbred line, WCZ, to construct F₂ and BC₁ segregating populations and to analyze the genetic characterization of watermelon stripe. Genetic analysis showed that the intermittent stripe was a qualitative trait and controlled by a single dominant gene, ClIS. Fine mapping based on linkage analysis showed that the ClIS gene was located on the 160 Kb regions between 25.92 Mb and 26.08 Mb on watermelon chromosome 6. Furthermore, another inbred watermelon line with intermittent stripe, FG, was re-sequenced and aligned on the region of 160 Kb. Interestingly, only two SNP variants (T/C, A/T) were present in both WT20 and FG inbred lines at the same time. The two SNPs are located in 25,961,768 bp (T/C) and 25,961,773 bp (A/T) of watermelon chromosome 6, which is located in the promoter region of Cla019202. We speculate that Cla019202 is the candidate gene of ClIS which controls the intermittent stripe in watermelon. In a previous study, the candidate gene ClGS was proved to control dark green stripe in watermelon. According to the verification of the two genes ClIS and ClGS in 75 watermelon germplasm resources, we further speculate that the ClGS gene may regulate the color of watermelon stripe, while the ClIS gene regulates the continuity of watermelon stripe. The study provides a good entry point for studying the formation of watermelon rind patterns, as well as providing foundation insights into the breeding of special appearance quality in watermelon.

The plant-specific IQ67 domain (IQD) is the largest class of calmodulin targets found in plants, and plays an important role in many biological processes, especially fruit development processes. However, the functional role of IQD proteins in the development of watermelon (Citrullus lanatus) shape remains unknown, as the IQD protein family in watermelon has not been systematically characterized. Herein, we elucidated the gene structures, chromosomal locations, evolutionary divergence, and functions of 35 IQD genes in the watermelon genome. The transcript profiles and quantitative real-time PCR analysis at different stages of fruit development showed that the ClIQD24 gene was highly expressed on 0 days after pollination. Furthermore, we found that the ectopic overexpression of ClIQD24 promoted tomato fruit elongation, thereby revealing the significance of ClIQD24 in the progression of watermelon shape. Our study will serve as a reference for further investigations on the molecular mechanisms underlying watermelon fruit shape formation.

The aerial parts of most land plants are covered with cuticular wax which is important for plants to avoid harmful factors. There is still no cloning study about wax synthesis gene of the alcohol-forming pathway in Brassica species. Scanning electron microscopy (SEM) showed that, compared with wild type (WT), wax crystal are severely reduced in both the adaxial and abaxial sides of cabbage (Brassica oleracea L. var. capitata L.) leaves from the LD10GL mutant. Genetic analysis results revealed that the glossy trait of LD10GL is controlled by a single recessive gene, and fine mapping results revealed that the target gene Cgl2 (Cabbage glossy 2) is located within a physical region of 170 kb on chromosome 1. Based on sequence analysis of the genes in the mapped region, the gene designated Bol013612 was speculated to be the candidate gene. Gene Bol013612 is homologous to Arabidopsis CER4, which encodes fatty acyl-coenzyme A reductase. Sequencing identified a single nucleotide substitution at an intron/exon boundary that results in an insertion of six nucleotides in the cDNA of Bol013612 in LD10GL. The phenotypic defect of LD10GL was confirmed by a functional complementation test with Arabidopsis mutant cer4. Our results indicated that wax crystals of cabbage mutant LD10GL are severely reduced and mutation of gene Bol013612 causes a glossy phenotype in the LD10GL mutant.