Two Different Types of Anthocyanin-less Leaves in Fittonia

Abstract

Fittonia albivenis (Lindl. ex Veitch) is a popular ornamental plant because of its dark green leaf blades and white, pink or red veins. This study aimed to anlayze the difference between red vein leaves and white vein leaves. By HPLC analysis, pelargonidin was detected from all red-vein cultivars, while no anthocyanins were detected from all white-vein cultivars, indicating vein pigmentation is due to the presence or absence of anthocyanin. Interestingly, white-vein cultivars were classified into two types: one type accumulated flavone in leaves (‘White Star’, ‘Snow Anne’, and ‘White Tiger’), and the other type did not accumulate any flavonoids in leaves (‘Sunny Green’ and ‘Sunny Yellow’). The flavone-accumulating ‘White Star’ did not show any major difference in anthocyanin biosynthetic gene expression compared to red-vein cultivars, but did have a stop codon mutation in anthocyanidin synthase (ANS). ANS cDNA of ‘White Star’ and ‘Snow Anne’ had a premature stop codon at 290^th bp, and ANS cDNA of ‘White Tiger’ had a premature stop codon at 943^rd bp due to an A-insertion at 790^th bp, resulting in a truncated ANS protein. On the other hand, a flavonoid-less cultivar, ‘Sunny Green’, showed lower expression levels of anthocyanin biosynthetic genes than red-vein cultivars, especially for chalcone synthase 1 (CHS1), chalcone isomerase (CHI), flavanone 3-hydroxylase (F3H), and dihydroflavonol 4-reductase (DFR). The expression level of flavone synthase (FNS) was not significantly different from red-vein cultivars and cDNA of FNS appeared to encode full-length protein, indicating the anthocyanin-less and flavone-less phenotype is due to CHS1, CHS2 or CHI steps. As for CHS2, ‘Sunny Green’ expressed intron-inserted CHS2 resulting in a truncated protein; however, this transcript was detected from other cultivars. From these results, it was suggested that low expression of CHS1 and CHI was important for flavonoid-less leaves in ‘Sunny Green’. In addition, ‘Sunny Green’ did not express full-length F3H transcripts. Therefore, multiple independent mutations in anthocyanin biosynthetic genes contribute to anthocyanin-less leaves in fittonia.