Peris, A. | bioRxiv Science

bioRxiv2022

Biosynthesis and apoplast accumulation of the apocarotenoid pigment azafrin in parasitizing roots of Escobedia grandiflora

O_LIThe herbaceous hemiparasite Escobedia grandiflora (Orobanchaceae) is used in traditional medicine in the Andean region. Their roots accumulate an orange pigment with a significant relevance as a cooking dye that exhibits antioxidant and cardioprotective properties. C_LIO_LIThe present work combined metabolic and cytological analyses with de novo transcriptome assembly, gene expression studies, and phylogenetic analyses to confirm the chemical identity of the pigment and investigate its biosynthesis and function in Escobedia roots. C_LIO_LIThe pigment was conclusively shown to be azafrin, an apocarotenoid likely derived from the cleavage of {beta}-carotene. Candidate genes for the production of azafrin in Escobedia roots are proposed based on RNA-seq supported by RT-qPCR and phylogeny reconstruction analyses. In particular, our data suggest that azafrin production relies a carotenoid cleavage dioxygenase (CCD) different from CCD7 and similar to CCD4 enzymes. We also show that azafrin is delivered to the root apoplast and that it accumulates in the area where the Escobedia haustorium contacts the hosts root, suggesting a role of azafrin in the parasitization process. C_LIO_LIAltogether, our work represents an unprecedented step forward in our understanding of the Escobedia parasitization system, but it also provides vital information towards the eventual domestication of this valuable medicinal plant. C_LI

plant biology↗

bioRxiv2021

The grape MYB24 mediates the coordination of light-induced terpene and flavonol accumulation in response to berry anthocyanin sunscreen depletion

The presence of naturally-occurring color mutants in plants has permitted the identification of many regulatory genes implicated in the synthesis of discrete metabolic compounds, mostly anthocyanins and carotenoids. Conversely, transcription factors that coordinate more than one specialized metabolic pathway seem challenging to screen from a forward genetics perspective. We explored the relationship between different branches of the phenylpropanoid and isoprenoid pathways while examining an infrequent berry skin color variegation in grapevine. Red and white berry skin sections were compared at the genetic, transcriptomic and metabolomic levels showing that, as in most cultivated white grape varieties, the uncolored skin section convened the non-functional alleles of the anthocyanin regulators MYBA1 and MYBA2, explaining the lack of pigments. In contrast, light-responsive flavonols and monoterpenes increased in anthocyanin-depleted areas. We disclosed an enrichment of the flavonol, terpene and carotenoid pathways among up-regulated genes from white-skin sections, accompanied by increased expressions of flavonol regulators and the still uncharacterized MYB24 gene. We used DAP-seq to examine the in vitro binding of affinity-purified MYB24 protein to genomic DNA and demonstrated its binding in the promoter regions of terpene (22) and carotenoid (6) genes, in addition to more than 30 photosynthesis and light-response genes, including the flavonol-regulator HY5 homologue (HYH). We confirmed the activation of TPS35 and HYH promoter:luciferase reporters in the presence of MYB24 and the grape bHLH MYC2, all of which correlate in their higher expression in white skin variegated sections. The integration of several datasets allowed to define a list of high confidence targets, suggesting MYB24 as a modulator of light responses including the synthesis of flavonoids (flavonols) and isoprenoids (terpenes, and putatively carotenoids). The correspondence between MYB24 and monoterpenes in all conditions surveyed implies that this regulatory network is broadly triggered towards berry ripening, and that the absence of anthocyanin sunscreens accelerates its activation most likely in a dose-dependent manner due to increased radiation exposure.

plant biology↗