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Introduction
Shiitake mushroom (Lentinus edodes) is deeply loved by consumers because of its high nutritional value and delicious flavor
.
Spore release is one of
the hallmarks of its aging.
The flavor of shiitake mushrooms is not only pleasurable to consumers' senses, but also related to
spore release.
At the molecular level, the relationship between energy state and umami level during spore release has been poorly reported
.
Professor Xin Guang, Xia Rongrong, Zhao Xuemei of the College of Food Science, Shenyang Agricultural University, etc.
studied the energy level and umami substance changes of shiitake mushrooms at room temperature during different storage periods and analyzed the correlation, and identified the differentially expressed genes
related to energy and umami metabolism during spore release based on transcriptome sequencing.
This paper aims to reveal the molecular mechanism relationship between energy state and umami substances during postharvest spore release, and provide valuable insights
into the relationship between umami state and energy substance metabolism during postharvest spores release.
Results and Discussion
Changes in Storage Quality When shiitake mushrooms were stored at 25 °C for 12 h, the cap was slightly opened (Figure 1A), and slight spore prints
were photographed for the first time at 24 h.
During 36~60 h, a large number of spore releases
were observed.
The respiration rate peaked at 24 h (P<0.
05), which coincided with the first release phase of the spores (Figure 1B).
<b111> After removal from the nutrient matrix, the respiration of the mushroom increases, and the respiration must depend on the consumption of nutrients in the body to satisfy the energy supply
.
With the release of mushroom spores and the opening of the lid, weightlessness continues to increase (Figure 1C).
Thus, the spore release of the mushroom is triggered at 24 h, corresponding to the peak of respiration at the beginning of mushroom senescence
.
In this paper, the energy level and umami substance changes
during shiitake mushroom storage were also determined.
Fig.
1 Changes in appearance (A), respiration rate (B) and weightlessness (C) during storage Correlation analysis Correlation analysis showed that ATP and AMP contents were significantly correlated with GMP and Glu content (P<0.
05).
<b116> Amino acids contribute to mitochondrial metabolism and ATP production, where the carbon backbone is normally converted into a precursor or intermediate for the TCA cycle
.
The correlation
between umami compound content and energy metabolism-related enzyme activities was analyzed.
Glu content was negatively correlated with G-6-PDH and SDH activity (P<0.
05), while Asp content was positively correlated with SDH and CCO activity (P<0.
01).
<b119> SDH may be an important enzyme
influencing the umami taste of harvested mushrooms.
EC and EUC showed a significant positive correlation (P<0.
001).
<b121> Therefore, umami compound levels are closely related
to the energy state during the release of mushroom spores.
Fig.
2 Pearson correlation coefficient (R) matrix of energy status and umami compound content of shiitake mushrooms during storage Transcriptomic analysis LeGALM, LeGADPH, LePGK and LePK genes were significantly downregulated at 24 h, resulting in a decrease in pyruvate content (Fig.
3A).
Pyruvate is an important raw material
for the TCA pathway.
Energy production is primarily associated with mitochondrial reactions such as TCA and mETC pathways
.
The LeSDH, LeIDH and LeACLY genes in the TCA pathway were downregulated
at 24 h.
The expression of LenuoA, LefbcH1, LefbcH2 and LeCCO in the mETC pathway was significantly downregulated
at 24 h.
Fifteen energy metabolism genes were significantly downregulated, indicating that large amounts of energy expenditure triggered spore release
.
The LeACLY, LenuoA, LeALDH1 and LeALDH2 genes were significantly downregulated at 60 h, and the ATP content decreased
.
Therefore, the downregulation of ATP synthesis-related genes may be the cause of
mushroom aging.
As shown in Figure 3B, LeAK and LecpdP1, key genes for the conversion of ATP to AMP, were significantly upregulated
at 24 h.
LecpdP2, LenrdJ1, LenuD and LeADK were significantly downregulated at 24 h, inhibiting the decomposition
of ATP, AMP, IMP and XMP.
As can be seen from Figure 3C, the TCA cycle is an intermediate pathway for the synthesis and decomposition of Glu and Asp in the amino acid metabolism pathway
.
At 24 h, the expression of LeGLT and LegudB increased significantly, resulting in a large conversion of ketoglutaric acid to glutamate
.
The upregulation of LEGAD led to increased glutamate decomposition at 60 h, and the significantly downregulated LEASNS gene at 24 h and 60 h was negatively correlated with Asp content, resulting in increased
Asp production.
Genes for purine and amino acid metabolic pathways are significantly expressed, suggesting that energy status is associated
with umami at the molecular level.
The above data show that the metabolism of mushroom umami compounds during storage is regulated
by the energy state.
3 Effects of mushroom energy (A), purine (B) and amino acid (C) metabolism pathways during postharvest storage Conclusion
A slight spore pattern was observed in shiitake mushrooms stored at 25 °C at 24 hours postharvest, accompanied by peak respiration, significant decrease in ATP, and significant increase in energy-related enzyme activity, indicating that spore release consumes a lot of energy and is the beginning
of
postharvest senescence 。 At the same time, with the relatively high content of umami nucleotides and amino acids released by spores, correlation analysis showed that EUC was significantly correlated with energy status (R=0.
80).
Fifteen energy metabolism genes were significantly downregulated
during spore release.
LecpdP1 and LeAK are key genes that connect energy status to umami and are responsible for the conversion of ATP to AMP in the purine metabolic pathway
.
These new findings reveal the molecular mechanism of energy state changes during spore release and the relationship
between energy state and umami.
Future in-depth studies of other factors influencing spore release will provide clues
.
