Cloning and Expression Characterization Analysis of the Watermelon (Citrullus lanatus) Fruit Flesh Hardness Regulating Gene ClMADS37
ZHOU Mei-Han1,2, LIU Chen-Xin1,2, LIU Shi-Liang1,2, MA Ting-Ting1,2, JIA Yun-He1,2,3, WANG Xue-Zheng1,2,*
1 Key Laboratory of Biology and Germplasm Innovation of Horticultural Crops in Northeast China, Ministry of Agriculture and Rural Affairs, Harbin 150030, China; 2 College of Horticulture, Northeast Agricultural University, Harbin 150030, China; 3 Horticulture Branch of Heilongjiang Academy of Agricultural Sciences, Harbin 150030, China
Abstract：The MADS-box transcription factor family is widely involved in fruit ripening, cell wall remodeling, and texture regulation in plants, playing a central role in maintaining and softening fruit flesh. However, the molecular mechanisms of this family in regulating flesh hardness in watermelon (Citrullus lanatus) remain unclear. To investigate the regulatory function of MADS-box transcription factors in the formation of fruit flesh firmness in watermelon, fruit flesh tissues of the hard-flesh line '51' and the soft-flesh line '1338' were used as experimental materials. Through transcriptome analysis and qRT-PCR validation, a candidate gene associated with fruit flesh firmness, designated ClMADS37, was screened. The coding sequence of this gene was cloned, and its structural and expression characteristics were analyzed using bioinformatics methods. The results showed that the open reading frame (ORF) of ClMADS37 was 1 176 bp in length, encoding 391 amino acids. The protein was predicted to be an acidic, stable, hydrophilic protein localized in the nucleus. Expression analysis revealed that ClMADS37 expression levels in the flesh were significantly positively correlated with fruit firmness (r=0.7558). Furthermore, its expression was highest in stems and lowest in leaves. Promoter region analysis identified multiple light-responsive and hormone-responsive elements. In summary, ClMADS37 may positively regulate watermelon flesh hardness, and this study provides a theoretical basis and genetic resource for improving fruit texture and molecular breeding in watermelon.
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