Abstract
Flesh firmness of watermelon is an important quality trait for commercial fruit values, including fruit storability, transportability, and shelf life. To date, knowledge of the gene networks underlying this trait is still limited. Herein, we used weighted genes co-expression network analysis (WGCNA) based on correlation and the association of phenotypic data (cell wall contents) with significantly differentially expressed genes between two materials, a near isogeneic line “HWF” (with high average flesh firmness) and inbred line “203Z” (with low average flesh firmness), to identify the gene networks responsible for changes in fruit flesh firmness. We identified three gene modules harboring 354 genes; these gene modules demonstrated significant correlation with water-soluble pectin, cellulose, hemicellulose, and protopectin. Based on intramodular significance, eight genes involved in cell wall biosynthesis and ethylene pathway are identified as hub genes within these modules. Among these genes, two genes, Cla012351 (Cellulose synthase) and Cla004251 (Pectinesterase), were significantly correlated with cellulose (r2 = 0.83) and protopectin (r2 = 0.81); three genes, Cla004120 (ERF1), Cla009966 (Cellulose synthase), and Cla006648 (Galactosyltransferase), had a significant correlation with water-soluble pectin (r2 = 0.91), cellulose (r2 = 0.9), and protopectin (r2 = 0.92); and three genes, Cla007092 (ERF2a), Cla004119 (probable glycosyltransferase), and Cla018816 (Xyloglucan endotransglucosylase/hydrolase), were correlated with hemicellulose (r2 = 0.85), cellulose (r2 = 0.8), and protopectin (r2 = 0.8). This study generated important insights of biosynthesis of a cell wall structure and ethylene signaling transduction pathway, the mechanism controlling the flesh firmness changes in watermelon, which provide a significant source to accelerate future functional analysis in watermelon to facilitate crop improvement.
Highlights
Watermelon (Citrullus lanatus) is included in the genus Citrullus of the family Cucurbitaceae
The content of cellulose and hemicellulose shows an increased-decreased trend, and in HWF and 203Z, the trend of cellulose content in HWF and 203Z is opposite, increased in HWF with developmental stages while in 203Z decreased from the beginning 10 days after pollination (DAP), and there is no significant variation observed between HWF and 203Z during four developmental stages
We applied weighted gene co-expression network analysis (WGCNA) to manipulate a multivariate transcriptome dataset sampled from different developmental stages of two materials, HWF and 203Z
Summary
Watermelon (Citrullus lanatus) is included in the genus Citrullus of the family Cucurbitaceae. The quality of watermelon fruits is affected by many factors: fruit shape and size, rind thickness and color, flesh firmness and color, aroma, sugar contents, and carotenoids and flavonoids composition (Wechter et al, 2008). These qualities are further categorized into three main categories: commodity quality, sensory quality, and nutritional quality. Flesh firmness is the sensory quality of watermelon; the attribute is one of the important indicators to measure the commerciality, transportability, storability, and shelf life of fruits (Guo et al, 2015), the juiciness of fruits attributes to the fruit texture: if the fruit flesh is hard, the juice is low, and it provides poor mouth sensation (Harker et al, 2003). If the flesh is too soft, it will affect the degree of refreshment and shelf-life (Risse et al, 1990)
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