AUTHOR=Chen Daozong , Liu Yi , Yin Shuai , Qiu Jie , Jin Qingdong , King Graham J. , Wang Jing , Ge Xianhong , Li Zaiyun 

TITLE=Alternatively Spliced BnaPAP2.A7 Isoforms Play Opposing Roles in Anthocyanin Biosynthesis of Brassica napus L.

JOURNAL=Frontiers in Plant Science

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2020.00983

DOI=10.3389/fpls.2020.00983

ISSN=1664-462X

ABSTRACT=<p><italic>Brassica napus</italic> L. (rapeseed, oilseed rape, and canola) and varieties of its two diploid parents, <italic>B. oleracea</italic> and <italic>B. rapa</italic>, display a large amount of variation in anthocyanin pigmentation of the leaf, stem, and fruit. Here, we demonstrate that <italic>BnaPAP2.A7</italic>, an ortholog of the <italic>B. oleracea</italic> anthocyanin activator <italic>BoMYB2</italic> that confers purple traits, positively regulates anthocyanin biosynthesis in leaves of <italic>B. napus</italic>. Sequencing of <italic>BnaPAP2.A7</italic> and transgenic analysis suggests that activation of this gene in purple rapeseed may result from a single nucleotide and/or 2bp insertion in its promoter region. <italic>BnaPAP2.A7</italic> gives rise to three splice variants, designated <italic>BnaPAP2.A7-744, BnaPAP2.A7-910</italic>, and <italic>BnaPAP2.A7-395</italic> according to the length of the transcripts. While <italic>BnaPAP2.A7-744</italic> encodes a full-length R2R3-MYB, both <italic>BnaPAP2.A7-910</italic> and <italic>BnaPAP2.A7-395</italic> encode truncated proteins that lack both a partial R3 repeat and the complete C terminal domain, and so <italic>in vitro</italic> are unable to interact with the <italic>Arabidopsis</italic> bHLH protein AtTT8. Although expression of either <italic>BnaPAP2.A7-910</italic> or <italic>BnaPAP2.A7-395</italic> in green rapeseed does not result in purple leaves, both genes do modify genome-wide gene expression, with a strong repression of anthocyanin-related genes. We have demonstrated that <italic>BnaPAP.A7</italic> regulates anthocyanin accumulation in leaves of <italic>B. napus</italic> and propose a potential mechanism for modulation of anthocyanin biosynthesis by alternative splicing.</p>