Carotenoid Metabolomics in Ripening Tomatoes

We are very pleased to share a recent paper 'ETHYLENE INSENSITIVE 3-LIKE 2 regulates β-carotene and ascorbic acid in tomatoes during ripening' which published in Plant Physiology. This article reveals an important molecular regulatory mechanism of EIL2 regulating the accumulation of β-carotene and ascorbic acid in tomato fruits. Metwarebio has provided phytohormone and carotenoid detection and transcriptome analysis.

Ethylene regulates fruit ripening by orchestrating a transcriptional cascade of ethylene-responsive genes, including transcription factor genes in the ETHYLENE INSENSITIVE 3/ETHYLENE INSENSITIVE 3-LIKE (EIN3/EIL). Using CRISPR/Cas9 eil2 mutants and SlEIL2 RNAi lines (ERIs), the authors have discovered that EIL2 controls carotenoid metabolism and ascorbic acid biosynthesis in tomato. In contrast to the red fruits presented in the wild type (WT) 45 days after pollination (45DAA), the fruits of eil2 mutants and ERIs show yellow or orange fruits.

The major carotenoids in ripe tomato fruit are lycopene and β-carotene, and both compounds are highly beneficial for human health. Ascorbic acid, another abundant metabolite in tomato fruit, is involved in scavenging reactive oxygen species. Based on this study, decreased SlEIL2 expression in tomato fruit at the late ripening stage results in β-carotene accumulation. Besides, the content of neoxanthin, violaxanthin and ε-carotene and ascorbic acid show significant higher levels in the ERI fruits than that in the WT fruits at 45DAA, while lycopene, γ-carotene, lutein and phytoene show significant lower levels.

Further transcriptome analysis of the ERI and WT ripe fruits (45DAA) reveals that the carotenoid biosynthesis pathway is significantly enriched. To investigate the causal factor underlying the β-carotene and ascorbic acid changes, correlation analysis of combined transcriptome and metabolome data as well as gene function validation are performed and discover that SlEIL2 regulates the expression of ERFs, including ERF.H30 and ERF.G6, to affect SlLCYB2 transcript levels, thus controlling the conversion of lycopene to β-carotene and then enhancing the ABA accumulation. Meanwhile, SlEIL2 is also involved in the ascorbic acid biosynthetic pathway by regulating SlMIOX1 and SlGPP3/IMP3 expression. In conclusion, no matter LCYB or SlGPP3/IMP3 over expression fruits exhibit improved fruit firmness, delayed softening and extended shelf-life, SlEIL2 seems as a switch to control fruit softening and shelf-life. The elucidation of the regulatory mechanism of ascorbic acid and β-carotene biosynthetic routes will be important for improvement of the nutritional value and the storability of tomato.

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