MYB24 orchestrates terpene and flavonol metabolism as light responses to anthocyanin depletion in variegated grape berries.

Variegation is a rare type of mosaicism not fully studied in plants, especially fruits. We examined red and white sections of grape (Vitis vinifera cv. 'Béquignol') variegated berries and found that accumulation of products from branches of the phenylpropanoid and isoprenoid pathways showed an opposite tendency. Light-responsive flavonol and monoterpene levels increased in anthocyanin-depleted areas in correlation with increasing MYB24 expression. Cistrome analysis suggested that MYB24 binds to the promoters of 22 terpene synthase (TPS) genes, as well as 32 photosynthesis/light-related genes, including carotenoid pathway members, the flavonol regulator HY5 HOMOLOGUE (HYH), and other radiation response genes. Indeed, TPS35, TPS09, the carotenoid isomerase gene CRTISO2, and HYH were activated in the presence of MYB24 and MYC2. We suggest that MYB24 modulates ultraviolet and high-intensity visible light stress responses that include terpene and flavonol synthesis and potentially affects carotenoids. The MYB24 regulatory network is developmentally triggered after the onset of berry ripening, while the absence of anthocyanin sunscreens accelerates its activation, likely in a dose-dependent manner due to increased radiation exposure. Anthocyanins and flavonols in variegated berry skins act as effective sunscreens but for different wavelength ranges. The expression patterns of stress marker genes in red and white sections of 'Béquignol' berries strongly suggest that MYB24 promotes light stress amelioration but only partly succeeds during late ripening.

Novel Glutamate-Putrescine Ligase Activity in Haloferax mediterranei: A New Function for glnA-2 Gene.

The genome of the halophilic archaea Haloferax mediterranei contains three ORFs that show homology with glutamine synthetase (GS) (glnA-1, glnA-2, and glnA-3). Previous studies have focused on the role of GlnA-1, suggesting that proteins GlnA-2 and GlnA-3 could play a different role to that of GS. Glutamine synthetase (EC 6.3.1.2) belongs to the class of ligases, including 20 subclasses of other different enzymes, such as aspartate-ammonia ligase (EC 6.3.1.1), glutamate-ethylamine ligase (EC 6.3.1.6), and glutamate-putrescine ligase (EC 6.3.1.11). The reaction catalyzed by glutamate-putrescine ligase is comparable to the reaction catalyzed by glutamine synthetase (GS). Both enzymes can bind a glutamate molecule to an amino group: ammonium (GS) or putrescine (glutamate-putrescine ligase). In addition, they present the characteristic catalytic domain of GS, showing significant similarities in their structure. Although these proteins are annotated as GS, the bioinformatics and experimental results obtained in this work indicate that the GlnA-2 protein (HFX_1688) is a glutamate-putrescine ligase, involved in polyamine catabolism. The most significant results are those related to glutamate-putrescine ligase's activity and the analysis of the transcriptional and translational expression of the glnA-2 gene in the presence of different nitrogen sources. This work confirms a new metabolic pathway in the Archaea domain which extends the knowledge regarding the utilization of alternative nitrogen sources in this domain.