Abstract
Flavonoids influence the flavor and nutritional value of pecan nuts. However, limited information is available regarding the molecular mechanisms underlying pecan flavonoid biosynthesis. Here, we used a high (“YLC28”) and a low (“Oconee”) flavonoid content cultivar as the research objects. The changes in flavonoid content and the gene transcription patterns during kernel development were identified. Different accumulation patterns of total flavonoids (TF) and condensed tannins (CT) were observed between the two cultivars. The contents of TF and CT in “YLC28” were 1.76- and 2.67-fold higher levels than that of “Oconee” on 150 days after full bloom of female flowers, respectively. In total, 30 RNA-Seq libraries were constructed and sequenced. The upregulated genes in “YLC28” were highly enriched in flavonoid-related pathways. Thirty-three structural genes were identified, and the expression of two phenylalanine ammonia lyases, one chalcone synthase, one flavonoid 3’,5’-hydroxylase, and one flavonol synthase exhibited high correlation (r ≥ 0.7, p < 0.01) with the condensed tannin content in “YLC28.” A putative MYB transcription factor, CIL1093S0100, might act as a flavonoid biosynthesis repressor during kernel development. Altogether, these results will be useful for uncovering the molecular mechanisms of flavonoid biosynthesis and subsequently accelerating quality pecan breeding.
Highlights
The numbers were three, one, seven, two, one, six, and two, respectively. These results further suggested that the different expression patterns of flavonoid biosynthesis-related genes might account for the different total flavonoid (TF) and condensed tannin (CT) contents between the two genotypes
Yang et al (2018) reported that the transcription of F3H1, F3’H1, ANS1, UFGT1, and chalcone synthase (CHS) shared strong correlations in wintersweet flower. These results indicated that the remarkably different accumulation profiles of flavonoids between “YLC28” and “Oconee” resulted from the distinct gene expression patterns
The results showed that the biological replicates were grouped together (Supplementary Figure 1), which suggested a good correlation between replicates
Summary
The contents of phenolic components in pecan kernels exhibited intercultivar variation (Venkatachalam and Sathe, 2006; Villarreal-Lozoya et al, 2007; Zhang et al, 2019b; Bouali et al, 2020). The contents of total phenolics and condensed tannins showed at most 1.71- and 1.88-fold differences among the six pecan cultivars, respectively (Villarreal-Lozoya et al, 2007). Because phenolics are the major antioxidant phytochemicals in pecan (Villarreal-Lozoya et al, 2007; de la Rosa et al, 2011), the nuts from different varieties present different nutritive values and different implications for health promotion (Bouali et al, 2020). Verifying the genetic regulation of its metabolism will be helpful for understanding the quality formation mechanism and will promote genetic improvement in this plant
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