Integrated transcriptome and metabolome analysis reveals the regulation of phlorizin synthesis in Lithocarpus polystachyus under nitrogen fertilization.

BACKGROUND: Nitrogen (N) is essential for plant growth and development. In Lithocarpus polystachyus Rehd., a species known for its medicinal and food value, phlorizin is the major bioactive compound with pharmacological activity. Research has revealed a positive correlation between plant nitrogen (N) content and phlorizin synthesis in this species. However, no study has analyzed the effect of N fertilization on phlorizin content and elucidated the molecular mechanisms underlying phlorizin synthesis in L. polystachyus. RESULTS: A comparison of the L. polystachyus plants grown without (0 mg/plant) and with N fertilization (25, 75, 125, 175, 225, and 275 mg/plant) revealed that 75 mg N/plant fertilization resulted in the greatest seedling height, ground diameter, crown width, and total phlorizin content. Subsequent analysis of the leaves using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) detected 150 metabolites, including 42 flavonoids, that were differentially accumulated between the plants grown without and with 75 mg/plant N fertilization. Transcriptomic analysis of the L. polystachyus plants via RNA sequencing revealed 162 genes involved in flavonoid biosynthesis, among which 53 significantly differed between the N-treated and untreated plants. Fertilization (75 mg N/plant) specifically upregulated the expression of the genes phenylalanine ammonia-lyase (PAL), 4-coumarate-CoA ligase (4CL), and phlorizin synthase (PGT1) but downregulated the expression of trans-cinnamate 4-monooxygenase (C4H), shikimate O-hydroxycinnamoyltransferase (HCT), and chalcone isomerase (CHI), which are related to phlorizin synthesis. Finally, an integrated analysis of the transcriptome and metabolome revealed that the increase in phlorizin after N fertilization was consistent with the upregulation of phlorizin biosynthetic genes. Quantitative real-time PCR (qRT‒PCR) was used to validate the RNA sequencing data. Thus, our results indicated that N fertilization increased phlorizin metabolism in L. polystachyus by regulating the expression levels of the PAL, PGT1, 5-O-(4-coumaroyl)-D-quinate 3'-monooxygenase (C3'H), C4H, and HCT genes. CONCLUSIONS: Our results demonstrated that the addition of 75 mg/plant N to L. polystachyus significantly promoted the accumulation of flavonoids, including phlorizin, and the expression of flavonoid synthesis-related genes. Under these conditions, the genes PAL, 4CL, and PGT1 were positively correlated with phlorizin accumulation, while C4H, CHI, and HCT were negatively correlated with phlorizin accumulation. Therefore, we speculate that PAL, 4CL, and PGT1 participate in the phlorizin pathway under an optimal N environment, regulating phlorizin biosynthesis. These findings provide a basis for improving plant bioactive constituents and serve as a reference for further pharmacological studies.

Mating Systems of Single Families and Population Genetic Diversity of Endangered Ormosia hosiei in South China.

Ormosia hosiei is a tree species native to China that has been extensively used for ornamental and furniture purposes due to its valued timber. The mating system has substantial impact on genetic diversity and structure of plant natural population. Such information should be considered when planning tree planting for forest restoration. Here we used 12 microsatellite markers and described the mating system of single families and the population genetic diversity of O. hosiei. A high level of genetic diversity was observed in both adults and progenies, although slight differences existed among populations and their progenies, with the expected heterozygosity ranging from 0.763 to 0.794. Overall, O. hosiei displayed a predominantly outcrossed mating. The estimate of multi-locus outcrossing rate (tm) was high with low variations among families, ranged from 0.997 to 1.000. The value of tm-ts, ranged from 0.000 to 0.139, indicated that biparental inbreeding occurred in progenies. Therefore, to obtain a reasonable genetic representation of native tree species and prevent problems associated with inbreeding depression, we suggested effective in situ conservation by replanting seedlings, but seedling production for restoration purposes may require a much larger sampling effort than is currently used. Moreover, it is necessary to conduct further multiple population and multi-year experiments to verify our conclusions.