Abstract
The purple leaf pigmentation mainly associated with anthocyanins accumulation is common in Brassica but the mechanisms of its production and its potential physiological functions are poorly understood. Here, we performed the phenotypic, cytological, physiological, and comparative leaves transcriptome analyses of 11 different varieties belonging to five Brassica species with purple or green leaves. We observed that the anthocyanin was accumulated in most of vegetative tissues in all species and also in reproduction organs of B. carinata. Anthocyanin accumulated in different part of purple leaves including adaxial and abaxial epidermal cells as well as palisade and spongy mesophyll cells. Leave transcriptome analysis showed that almost all late biosynthetic genes (LBGs) of anthocyanin, especially Dihydroflavonol 4-Reductase (DFR), Anthocyanidin Synthase (ANS) and Transparent Testa 19 (TT19), were highly up-regulated in all purple leaves. However, only one of transcript factors in anthocyanin biosynthesis pathway, Transparent Testa 8 (TT8), was up regulated along with those genes in all purple leaves, indicating its pivotal role for anthocyanin production in Brassica. Interestingly, with the up-regulation of genes for anthocyanin synthesis, Cytosolic 6-phosphogluconolactonase (PLG5) which involved in the oxidative pentose-phosphate pathway was up-regulated in all purple leaves and three genes FTSH PROTEASE 8 (FTS8), GLYCOLATE OXIDASE 1 (GOX1), and GLUTAMINE SYNTHETASE 1;4 (GLN1;4) related to degradation of photo-damaged proteins in photosystem II and light respiration were down-regulated. These results highlighted the potential physiological functions of anthocyanin accumulation related to photosynthesis which might be of great worth in future.
Highlights
Anthocyanins are water soluble pigment existing in many plants, algae, and bacteria
All cultivars used in the study have yellow endosperms and dark seed coat except for BcaP which has a brown to yellow seed coat
Comparative transcriptome analysis between paired green and purple leaves of 11 varieties belonging to five different species clearly showed that the most of anthocyanin biosynthesis genes were greatly up-regulated, especially for those Later biosynthesis genes (LBG) (Figure 7). These results indicated that anthocyanin accumulation in different part of leaves of different species might results from the variation of regulators involved in MYB–basic Helix-Loop-Helix (bHLH)– WD repeat (WDR) (MBW) complex which regulating LBGs
Summary
Anthocyanins are water soluble pigment existing in many plants, algae, and bacteria. These are responsible for various color formation in leaves, flowers, stems, roots, and many other plant organs which usually attract pollinators and dispersers. Plants under stress conditions or infection by pathogens could induce anthocyanins formation (Chalker-Scott, 1999; Lea et al, 2007; Kerio, 2011). These pigments are highly essential for plant survival. A number of studies have suggested that the food with rich anthocyanins could benefit human health by its high antioxidant activity against cardiovascular disease, certain cancer, and some other chronic diseases (Hou, 2003; Butelli et al, 2008; Martin et al, 2011; Lila, 2004)
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