ABSTRACT
Although Al3+-toxicity is one of the limiting factors for crop production in acidic soils, little is known about the Al3+-tolerance mechanism in watermelon, a fairly acid-tolerant crop. This work aimed to identify the interaction between the H2O2 scavenging pathway and auxin glycosylation relevant to watermelon Al3+-tolerance. By analyzing expressions of hormone-related ClUGTs and antioxidant enzyme genes in Al3+-tolerant (ZJ) and Al3+-sensitive (NBT) cultivars, we identified ClUGT75s (B1, B2, and D1) and ClSOD1-2-ClCAT as crucial components associated with Al3+-tolerance. Al3+-stress significantly increased H2O2 content by 92.7% in NBT and 42.3% in ZJ, accompanied by less Al3+-, auxin (IAA and IBA), and MDA contents in ZJ than NBT. These findings coincided with significant ClSOD1-2 expression and stable dismutation activity in NBT than ZJ. Hence, higher H2O2 content in the root apex of NBT than ZJ correlated with a significant increase in auxin content and ClSOD1-2 up-regulation. Moreover, Al3+-activated ClUGT75D1 and ClUGT75B2 in ZJ coincided with no considerable change in IBA content, suggesting that glycosylation-mediated changes in IBA content might be relevant to Al3+-tolerance in watermelon. Furthermore, exogenous H2O2 and IBA indicated ClUGT75D1 modulating IBA is likely dependent on H2O2 background. We hypothesize that a higher H2O2 level in NBT represses ClUGT75, resulting in increased auxin than those in ZJ roots. Thus, excess in both H2O2 and auxin aggravated the inhibition of root elongation under Al3+-stress. Our findings provide insights on the permissive action of H2O2 in the mediation of auxin glycosylation by ClUGT75 in root apex for Al3+-tolerance in watermelon.
Subject(s)
Citrullus , Indoleacetic Acids , Citrullus/genetics , Glycosylation , Hydrogen Peroxide , Plant RootsABSTRACT
Objective: To study the biosynthesis mechanism and transshipment law of limonin compounds in Citri Reticulatae Semen, traditional medicinal variety Citrus reticulata "Dahongpao". Methods: In the process of seed growth and development, the contents of limonin, nomilin, and obacunone in stem, vane, peel, and seeds were determined by UPLC tangerine; Using grey relational analysis method, the correlation analysis between the contents and the cloning of squalene synthase gene (ss), squalene epoxidase gene (se), and glucose transferase (lgt) expression was performed. Results: Limonin compounds in different organs had the largest accumulation in seeds; The accumulation of limonin compounds in different organs was significantly correlated with ss, se, and lgt gene expression, but in the seeds the accumulation of limonin has the most closely correlation with ss, se, and lgt gene expression; The ss gene expression had the largest contribution on the accumulation of limonin, nomilin, and obacunone. Conclusion: The study provides reliable and scientific envidendce for the synthesis mechanism and transshipment law of limonin compounds.
ABSTRACT
The Persian walnut (Juglans regia L.), a diploid species native to the mountainous regions of Central Asia, is the major walnut species cultivated for nut production and is one of the most widespread tree nut species in the world. The high nutritional value of J. regia nuts is associated with a rich array of polyphenolic compounds, whose complete biosynthetic pathways are still unknown. A J. regia genome sequence was obtained from the cultivar 'Chandler' to discover target genes and additional unknown genes. The 667-Mbp genome was assembled using two different methods (SOAPdenovo2 and MaSuRCA), with an N50 scaffold size of 464 955 bp (based on a genome size of 606 Mbp), 221 640 contigs and a GC content of 37%. Annotation with MAKER-P and other genomic resources yielded 32 498 gene models. Previous studies in walnut relying on tissue-specific methods have only identified a single polyphenol oxidase (PPO) gene (JrPPO1). Enabled by the J. regia genome sequence, a second homolog of PPO (JrPPO2) was discovered. In addition, about 130 genes in the large gallate 1-ß-glucosyltransferase (GGT) superfamily were detected. Specifically, two genes, JrGGT1 and JrGGT2, were significantly homologous to the GGT from Quercus robur (QrGGT), which is involved in the synthesis of 1-O-galloyl-ß-d-glucose, a precursor for the synthesis of hydrolysable tannins. The reference genome for J. regia provides meaningful insight into the complex pathways required for the synthesis of polyphenols. The walnut genome sequence provides important tools and methods to accelerate breeding and to facilitate the genetic dissection of complex traits.
