Abstract
BackgroundAnanas comosus var. bracteatus is a colorful plant used as a cut flower or landscape ornamental. The unique foliage color of this plant includes both green and red leaves and, as a trait of interest, deserves investigation. In order to explore the pigments behind the red section of the chimeric leaves, the green and red parts of chimeric leaves of Ananas comosus var. bracteatus were sampled and analyzed at phenotypic, cellular and molecular levels in this study.ResultsThe CIELAB results indicated that the a* values and L* values samples had significant differences between two parts. Freehand sections showed that anthocyanin presented limited accumulation in the green leaf tissues but obviously accumulation in the epidermal cells of red tissues. Transcriptomic and metabolomic analyses were performed by RNA-seq and LC-ESI-MS/MS. Among the 508 identified metabolites, 10 kinds of anthocyanins were detected, with 6 significantly different between the two samples. The cyanidin-3,5-O-diglucoside content that accounts for nearly 95.6% in red samples was significantly higher than green samples. RNA-Seq analyses showed that 11 out of 40 anthocyanin-related genes were differentially expressed between the green and red samples. Transcriptome and metabolome correlations were determined by nine quadrant analyses, and 9 anthocyanin-related genes, including MYB5 and MYB82, were correlated with 7 anthocyanin-related metabolites in the third quadrant in which genes and metabolites showing consistent change. Particularly, the PCCs between these two MYB genes and cyanidin-3,5-O-diglucoside were above 0.95.ConclusionPhenotypic colors are closely related to the tissue structures of different leaf parts of Ananas comosus var. bracteatus, and two MYB transcription factors might contribute to differences of anthocyanin accumulation in two parts of Ananas comosus var. bracteatus chimeric leaves. This study lay a foundation for further researches on functions of MYBs in Ananas comosus var. bracteatus and provides new insights to anthocyanin accumulation in different parts of chimeric leaves.
Highlights
Ananas comosus var. bracteatus is a colorful plant used as a cut flower or landscape ornamental
Anthocyanin biosynthesis is mainly regulated by MYB, basic helix-loop-helix and WD40 transcription factors, which form a complex to directly bind with promoters of anthocyanin biosynthetic genes, such as chalcone synthesis (CHS), chalcone isomerase (CHI), flavanone 3-hydroxylase (F3H), flavonoid 3′-hydroxylase (F3′H), flavonoid 3′5′-hydroxylase (F3′5′H), dihydroflavonol 4-reductase (DFR), anthocyanidin reductase (ANS) and UDP-glucose: flavonoid 3-O-glucosyltransferase (3GT) [6,7,8]
Leaf coloration The distribution of the color values of the green central parts (GR) and red edges (RE) samples was determined with the CIELAB coordinates: The L* values ranged from 46.03 to 77.42, the a* values ranged from − 5.68 to 23.58, the b* values ranged from 14.55 to 17.40, and the C* values ranged from 15.40 to 28.42 (Fig. 1)
Summary
Ananas comosus var. bracteatus is a colorful plant used as a cut flower or landscape ornamental. In order to explore the pigments behind the red section of the chimeric leaves, the green and red parts of chimeric leaves of Ananas comosus var. Anthocyanin biosynthesis is mainly regulated by MYB, basic helix-loop-helix (bHLH) and WD40 transcription factors, which form a complex to directly bind with promoters of anthocyanin biosynthetic genes, such as chalcone synthesis (CHS), chalcone isomerase (CHI), flavanone 3-hydroxylase (F3H), flavonoid 3′-hydroxylase (F3′H), flavonoid 3′5′-hydroxylase (F3′5′H), dihydroflavonol 4-reductase (DFR), anthocyanidin reductase (ANS) and UDP-glucose: flavonoid 3-O-glucosyltransferase (3GT) [6,7,8]. According to previous reports about anthocyanin related transcription factors in Arabidopsis thaliana, the MYB transcription factor TRANSPARENT TESTA 2 (TT2) regulates the expression of late biosynthesis genes to pigment the seed coat by combining with factors TT8 (bHLH42) and TTG1 (WD40) [12, 13]. The molecular mechanism of anthocyanin accumulation in Ananas comosus var. bracteatus leaves is still largely unknown
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