Dwarfism is one of the most valuable traits in watermelon breeding mainly because of its contribution to yield as well as the decreased labor required to cultivate and harvest smaller plants. However, the underlying genetic mechanism is unknown. In this study, a candidate dwarfism gene was identified by applying next-generation sequencing technology to analyze watermelon plants. We completed a whole-genome re-sequencing of two DNA bulks (dwarf pool and vine pool) generated from plants in an F2 population. A genome-wide analysis of single nucleotide polymorphisms resulted in the detection of a genomic region harboring the candidate dwarfism gene Cla010726. The encoded protein was predicted to be a gibberellin 20-oxidase-like protein, which is a well-known “green revolution” protein in other crops. A quantitative real-time PCR investigation revealed that the Cla010726 expression level was significantly lower in the dwarf plants than in the normal-sized plants. The SNP analysis resulted in two SNP locating in the Cla010726 gene promoter of dsh F2 individuals. The results presented herein provide preliminary evidence that Cla010726 is a possible dwarfism gene.

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Background: In recent years, nickel (Ni) has been widely applied in industrial and agricultural production and has become a kind of environmental pollution. In this study, the effect of nickel chloride (NiCl 2 ) with different concentrations on Arabidopsis genomic stability and DNA methylation has been demonstrated. The nucleolus variation and 18S rDNA methylation after NiCl 2 treatment have been analyzed.Results: The results are as follows: (1) The NiCl 2 could result in heritable genomic methylation variations. The genomic DNA methylation variations have been detected by methylation-sensitive amplified polymorphism (MSAP) molecular markers, and the result showed that after NiCl 2 treatment, there was methylation variation in T 0 generation seedlings, and partial site changes maintained in T 1 generation, which suggested that the effects of NiCl 2 on DNA methylation could be heritable in offspring. (2) NiCl 2 brought deformity and damage to nucleolar structure in Arabidopsis root tip cells, and the damage was positively correlated with the NiCl 2 concentration. 3. In the nucleolus, there was an increased cytosine methylation in 18S rDNA. The plant nucleolus variation and 18S rDNA methylation may be used as an examination indicator for Ni pollution in soil or plant. Conclusions: NiCl 2 application caused variation of DNA methylation of the Arabidopsis genomic and offspring's. NiCl 2 also resulted in nucleolar injury and deformity of root tip cells. The methylation rate of 18S rDNA also changed by adding NiCl 2 .

DNA methylation is an epigenetic modification involving many biological processes. It is known that epigenetic mechanisms such as cytosine methylation play a pivotal role in regulating plant development. In this current study, a conservative domainspliced hairpin RNA (ihpRNA) plant expression vector aimed at gene of DNA METHYLTRANSFERASE1 (CmMET1) has been constructed. Transgenic chrysanthemum materials (Zijingling) were obtained by Agrobacterium-mediated transformation with expression vectors. Transgenic plants were used as rootstock, grafted onto non-transgenic the scions [Guoqinghong (GQH) and Huanshuijinqiu (HSJQ)], which silencing CmMET1 gene, and exhibited the early flower phenotypes. A highperformance liquid chromatography analysis indicated that the decrease of CmMET1 expression decreased the methylation level of genomic DNA. Similarly, a quantitative real-time polymerase chain reaction analysis revealed that CmMET1 expression levels decreased in transgenic chrysanthemum plants and in the scions grafted onto transgenic plants. This decrease of CmMET1 expression upregulated the expression of the methyltransferase gene, METHYLTRANSFERASE2 (CmDRM2), but downregulated the expression of the demethylating enzyme gene, DEMETER (CmDME), while the CHROMOMETHY-LASEA (CmCMT3) expression level remained low and could be almost undetectable. Among the CmFT-likes genes that affect flowering time, CmFTL1 expression was downregulated, as well as CmFTL2 and CmFTL3 expression levels which were upregulated. Our data indicated that silencing CmMET1 could decrease plant height, change the phenotype of chrysanthemum, and promote earlier flowering. The transgenic plants bloomed 8 days earlier. GQH and HSJQ scions grafted onto transgenic plants were 12 and 9 days earlier than the scions grafted onto non-transgenic plants, respectively. Overall, the results have some meanings for promoting the flowering of chrysanthemum scion varieties using genetic modified rootstock.

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