ABSTRACT
Fruit ripening is usually accompanied by anthocyanin accumulation. Ethylene is key in ripening-induced anthocyanin production in many fruits. However, the effects of fruit ripening and ethylene on anthocyanin biosynthesis in purple tomato fruits are unclear. This study shows that bagged fruits of the purple tomato cultivar 'Indigo Rose' failed to produce anthocyanins at the red ripening stage after bag removal. In contrast, the bagged immature fruits accumulated a significant amount of anthocyanins after removing the bags. The transcriptomic analyses between immature and red ripening fruit before and after bag removal revealed that anthocyanin-related genes, including the key positive R2R3-MYB regulator SlAN2-like, were repressed in the red ripening fruit. The 86 identified transcription factors, including 13 AP2/ERF, 7 bZIP, 8 bHLH and 6 MYB, showed significantly different expressions between immature and red ripening fruits. Moreover, subjecting bagged immature fruits to exogenous ethylene treatment significantly inhibited anthocyanin accumulation and the expression of anthocyanin-related genes, including the anthocyanin structure genes and SlAN2-like. Thus, ethylene inhibits anthocyanin biosynthesis by repressing the transcription of SlAN2-like and other anthocyanin-related genes. These findings provide new insights into anthocyanin regulation in purple tomato fruit.
Subject(s)
Solanum lycopersicum , Anthocyanins/metabolism , Ethylenes/metabolism , Fruit/metabolism , Gene Expression Regulation, Plant , Solanum lycopersicum/genetics , Solanum lycopersicum/metabolism , Plant Proteins/genetics , Plant Proteins/metabolismABSTRACT
Anthocyanins are considered health-promoting phytonutrients; however, anthocyanins strictly occurr in the fruit peel of purple tomato cultivars, making the total anthocyanin content limited per tomato fruit. In this study, we performed a transcriptome analysis between the fruit peel and flesh of a purple tomato cultivar 'Indigo Rose' at both the mature green stage and breaking stage. In total, 1,945 differently expressed genes, including 165 transcription factors, were detected between the fruit peel and flesh, both at and after the mature green stage. We further analyzed the transcription of anthocyanin biosynthesis genes and the regulatory genes composing the MYB-bHLH-WD40 (MBW) complex between the fruit peel and flesh at both development stages. In addition, several light-sensing genes and other transcription factor genes, including BBX family genes and WRKY genes, showed different expression patterns between the fruit peel and flesh. These findings deepen our understanding of anthocyanin biosynthesis in tomato fruit peels and facilitate the identification of genes limiting the anthocyanin biosynthesis in tomato fruit flesh.
Subject(s)
Fruit/metabolism , Solanum lycopersicum/growth & development , Solanum lycopersicum/metabolism , Anthocyanins/metabolism , Fruit/genetics , Gene Expression Regulation, Plant/genetics , Gene Expression Regulation, Plant/physiology , Plant Proteins/genetics , Plant Proteins/metabolism , Transcription Factors/genetics , Transcription Factors/metabolismABSTRACT
KEY MESSAGE: Combining phenotype and gene expression analysis of the CRISPR/Cas9-induced SlAN2 mutants, we revealed that SlAN2 specifically regulated anthocyanin accumulation in vegetative tissues in purple tomato cultivar 'Indigo Rose.' Anthocyanins play an important role in plant development and also exhibit human health benefits. The tomato genome contains four highly homologous anthocyanin-related R2R3-MYB transcription factors: SlAN2, SlANT1, SlANT1-like, and SlAN2-like/Aft. SlAN2-like/Aft regulates anthocyanin accumulation in the fruit; however, the genetic function of the other three factors remains unclear. To better understand the function of R2R3-MYB transcription factors, we conducted targeted mutagenesis of SlAN2 in the purple tomato cultivar 'Indigo Rose' using clustered regularly interspersed short palindromic repeats/CRISPR-associated protein 9 (CRISPR/Cas9). The SlAN2 mutants had a fruit color and anthocyanin content similar to cv. 'Indigo Rose,' while the anthocyanin content and the relative expression levels of several anthocyanin-related genes in vegetative tissues were significantly lower in the SlAN2 mutant relative to cv. Indigo Rose. Furthermore, we found that anthocyanin biosynthesis is controlled by different regulators between tomato hypocotyls and cotyledons. In addition, SlAN2 mutants were shorter, with smaller and lighter fruits than cv. 'Indigo Rose.' Our findings further our understanding of anthocyanin production in tomato and other plant species.
