Abstract
Macadamia ternifolia is a dynamic oil-producing nut crop in the world. However, the nutshell is frequently considered as a low-quality material. Further, its metabolic profile is still uncharacterized. In order to explore the industrial significance of the nutshell, this study performed metabolic and transcriptomic analyses at various developmental stages of the nutshell. The qualitative and quantitative metabolic data analysis identified 596 metabolic substances including several species of phenolic acids, flavonoids, lipids, organic acids, amino acids and derivatives, nucleotides and derivatives, alkaloids, lignans, coumarins, terpenoids, tannins, and others. However, phenolic acids and flavonoids were predominant, and their abundance levels were significantly altered across various developmental stages of the nutshell. Comparative transcriptome analysis revealed that the expression patterns of phenolic acid and flavonoid pathway related genes were significantly changed during the nutshell growth. In particular, the expression of phenylalanine ammonia-lyase, C4H, 4CL, CHS, CHI, F3H, and FLS had dynamic differences at the various developmental stages of the nutshell. Our integrative metabolomic and transcriptomic analyses identified the key metabolic substances and their abundance levels. We further discussed the regulatory mechanism of phenolic and flavonoid biosynthesis in the nutshell of M. ternifolia. Our results provide new insights into the biological profiles of the nutshell of M. ternifolia and help to elucidate the molecular mechanisms of phenolic and flavonoid biosynthesis in the nutshell of M. ternifolia.
Highlights
Macadamia nuts belong to the Proteaceae family, native to Australia, and are considered one of the highest oil quality nuts in the world (Mast et al, 2008; Hu et al, 2019)
Class 5 had 51 metabolites that showed the highest abundance at the S1 stage, whereas classes 2, 4, and 6 contained 45, 56, and 57 metabolites, respectively. All metabolites of these classes exhibited the highest abundance during the S3 stage. These results indicated that phenolic acids and flavonoids are predominant metabolites in the nutshell
Our study showed that M. ternifolia had a diversity of metabolic compounds in the nutshell with polyphenols especially phenolic acids and flavonoids being the major metabolites present in the nutshell
Summary
Macadamia nuts belong to the Proteaceae family, native to Australia, and are considered one of the highest oil quality nuts in the world (Mast et al, 2008; Hu et al, 2019). It is commercially cultivated in China, Hawaii, South Africa, New Zealand, Kenya, and several South American countries (Rengel et al, 2015; Navarro and Rodrigues, 2016). There is a need to change the high amount of macadamia nutshell into useful by products to mitigate industrial based waste management problems
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