Differential Molecular Responses of Rapeseed Cotyledons to Light and Dark Reveal Metabolic Adaptations toward Autotrophy Establishment

TMT-based quantitative proteomic and physiological analyses on lotus plumule of artificially aged seed in long-living sacred lotus Nelumbo nucifera

Seed longevity is important for the maintenance of seed nutritional quality, vigor, and germination potential during storage. Sacred lotus is known as one of the longest living seeds in the world and their ability to maintain longevity has been widely investigated. In this study, a suitable controlled deterioration treatment (CDT) method was first established to evaluate the vigor loss of lotus plumule (LP), and then the Tandem Mass Tags (TMT)-based proteomic analysis was performed on LP from the CDT-treated seed to quantitatively and qualitatively analyze the protein profile dynamic. In total, 4002 proteins were successfully quantified, of them, 558 differently accumulated proteins (DAPs) were identified. Protein processing and RNA-related proteins were found more easily to be affected by CDT, which may directly result in seed vigor loss. Meanwhile, CDT resulted in remarkable up-regulation of numerous proteins related to antioxidation, photosynthesis, RNA and DNA stability, starch and sucrose mobilization, and cell membrane and wall stability, which potentially played key roles in maintaining the lotus seed vigor under CDT. Histological and physiological analyses were also performed to verify some proteome results. This study provided both fundamental data and new insights to further uncover the secret of lotus seed longevity. SIGNIFICANCE: Seed aging affects the seed quality and can result in direct economic losses. The exceptional longevity of sacred lotus seed has attracted extensive attention. In this study, an optimized CDT method was used to mimic the natural aging process of sacred lotus seed, and based on TMT-based quantitative proteomic analysis on the LP profile of CDT-treated seeds, a series of differentially accumulation of specific proteins (DEPs) were revealed related to CDT resistance. Correspondingly, the physiological state and histological structure of the LP along with the CDT were detected to verify the proteome data. This study provided comprehensive information for the molecular basis of lotus seed aging analysis and facilitate to screen seed longevity related proteins for other plant species.

Integration of metabolomics and transcriptomics analyses investigates the accumulation of secondary metabolites in maturing seed plumule of sacred lotus (Nelumbo nucifera)

Lotus seed plumule (LP) is rich in a variety of antioxidant and anti-inflammatory secondary metabolites, making it a traditional food and medicine widely used in China. Physiological and histological evidences indicated that LP mainly accumulated metabolites in 15-24 days after pollination (DAP) during their development. To systematically investigate the dynamic accumulation of major secondary metabolites, the UPLC-HRMS-based widely targeted metabolomics analyses were performed on maturing LP at 15, 18, 21, and 24 DAP. In total, 767 metabolites were identified, including many secondary metabolites, e.g., 27 % flavonoids and 8 % alkaloids. Among them, 591 were identified as differentially accumulated metabolites (DAMs). The majority of secondary metabolites showed great accumulation after 18 DAP even at the late stage of LP maturation, such as hesperidin, neohesperidin, orobol, serotonin, and lotus special O-nornuciferine, endowing mature LP with effective pharmaceutical properties. The paralleled transcriptomic analysis identified 11,019 differentially expressed genes (DEGs). Based on the comprehensive data, several systematical metabolic regulation maps were established for different secondary metabolites, and 18 DAP was found as a switching point for LP maturing from active primary metabolism to massive secondary metabolites deposition. This study provides valuable information for understanding the mechanism of secondary metabolite accumulation in maturing LP and facilitates its pharmaceutical application.

Cytological, genetic and transcriptomic characterization of a cucumber albino mutant

Photosynthesis, a fundamental process for plant growth and development, is dependent on chloroplast formation and chlorophyll synthesis. Severe disruption of chloroplast structure results in albinism of higher plants. In the present study, we report a cucumber albino alc mutant that presented white cotyledons under normal light conditions and was unable to produce first true leaf. Meanwhile, alc mutant could grow creamy green cotyledons under dim light conditions but died after exposure to normal light irradiation. No chlorophyll and carotenoid were detected in the alc mutant grown under normal light conditions. Using transmission electron microscopy, impaired chloroplasts were observed in this mutant. The genetic analysis indicated that the albino phenotype was recessively controlled by a single locus. Comparative transcriptomic analysis between the alc mutant and wild type revealed that genes involved in chlorophyll metabolism and the methylerythritol 4-phosphate pathway were affected in the alc mutant. In addition, three genes involved in chloroplast development, including two FtsH genes and one PPR gene, were found to have negligible expression in this mutant. The quality of RNA sequencing results was further confirmed by real-time quantitative PCR analysis. We also examined 12 homologous genes from alc mutant in other plant species, but no genetic variation in the coding sequences of these genes was found between alc mutant and wild type. Taken together, we characterized a cucumber albino mutant with albinism phenotype caused by chloroplast development deficiency and this mutant can pave way for future studies on plastid development.

Inhibition of glucose assimilation in Auxenochlorella protothecoides by light

BACKGROUND

The yield of microalgae biomass is the key to affect the accumulation of fatty acids. A few microalgae can assimilate organic carbon to improve biomass yield. In mixotrophic cultivation, microalgae can use organic carbon source and light energy simultaneously. The preference of the main energy source by microalgae determines the biomass yield. Auxenochlorella protothecoides is an oleaginous mixotrophic microalga that can efficiently assimilate glucose and accumulate a large amount of biomass and fatty acids. The current study focused on the effect of light on the growth and glucose assimilation of A. protothecoides.

RESULTS

In this study, we found that the uptake and metabolism of glucose in A. protothecoides could be inhibited by light, resulting in a reduction of biomass growth and lipid accumulation. We employed comparative proteomics to study the influence of light on the regulation of glucose assimilation in A. protothecoides. Proteomics revealed that proteins involving in gene translation and photosynthesis system were up-regulated in the light, such as ribulose-phosphate 3-epimerase and phosphoribulokinase. Calvin cycle-related proteins were also up-regulated, suggesting that light may inhibit glucose metabolism by enhancing the production of glyceraldehyde-3-phosphate (G3P) in the Calvin cycle. In addition, the redox homeostasis-related proteins such as thioredoxin reductase were up-regulated in the light, indicating that light may regulate glucose uptake by changing the redox balance. Moreover, the increase of NADH levels and redox potential of the medium under illumination might inhibit the activity of the glucose transport system and subsequently reduce glucose uptake.

CONCLUSIONS

A theoretical model of how glucose assimilation in A. protothecoides is negatively influenced by light was proposed, which will facilitate further studies on the complex mechanisms underlying the transition from autotrophy to heterotrophy for improving biomass accumulation.

Mechanical hulling and thermal pre-treatment effects on rapeseed oil antioxidant capacity and related lipophilic and hydrophilic bioactive compounds

In this study, the effect of rapeseed mechanical hulling and thermal pre-treatment by microwaves (from 2 to 10 min with 2-min intervals, 800 W) and roasting (from 20 to 100 min with 20-min intervals, 165 °C) on the content of phytochemicals in the oil was investigated. Results showed that both pre-treatments applied differentiated the oils in terms of the content of bioactive compounds. In general, oils pressed from hulled and thermally pre-treated seeds contained higher content of tocopherols, PC-8 and phytosterols, while oils pressed from non-hulled and pre-processed seeds had significantly higher concentration of polyphenols. Both microwaving and roasting contributed to an increase of antioxidant capacity of studied oils. The increase of radical scavenging activity of oils was seen mainly in hydrophilic fraction of oil, which was highly positively correlated with the amount of canolol formed during seeds heating.